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PCI/MSI: Add pci_enable_msi_range() and pci_enable_msix_range()
This adds pci_enable_msi_range(), which supersedes the pci_enable_msi()
and pci_enable_msi_block() MSI interfaces.
It also adds pci_enable_msix_range(), which supersedes the
pci_enable_msix() MSI-X interface.
The old interfaces have three categories of return values:
negative: failure; caller should not retry
positive: failure; value indicates number of interrupts that *could*
have been allocated, and caller may retry with a smaller request
zero: success; at least as many interrupts allocated as requested
It is error-prone to handle these three cases correctly in drivers.
The new functions return either a negative error code or a number of
successfully allocated MSI/MSI-X interrupts, which is expected to lead to
clearer device driver code.
pci_enable_msi(), pci_enable_msi_block() and pci_enable_msix() still exist
unchanged, but are deprecated and may be removed after callers are updated.
[bhelgaas: tweak changelog]
Suggested-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Alexander Gordeev
Bjorn Helgaas
parent
ff1aa430a2
commit
302a2523c2
@ -82,67 +82,97 @@ Most of the hard work is done for the driver in the PCI layer. It simply
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has to request that the PCI layer set up the MSI capability for this
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device.
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4.2.1 pci_enable_msi
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4.2.1 pci_enable_msi_range
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int pci_enable_msi(struct pci_dev *dev)
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int pci_enable_msi_range(struct pci_dev *dev, int minvec, int maxvec)
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A successful call allocates ONE interrupt to the device, regardless
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of how many MSIs the device supports. The device is switched from
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pin-based interrupt mode to MSI mode. The dev->irq number is changed
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to a new number which represents the message signaled interrupt;
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consequently, this function should be called before the driver calls
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request_irq(), because an MSI is delivered via a vector that is
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different from the vector of a pin-based interrupt.
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This function allows a device driver to request any number of MSI
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interrupts within specified range from 'minvec' to 'maxvec'.
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4.2.2 pci_enable_msi_block
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int pci_enable_msi_block(struct pci_dev *dev, int count)
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This variation on the above call allows a device driver to request multiple
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MSIs. The MSI specification only allows interrupts to be allocated in
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powers of two, up to a maximum of 2^5 (32).
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If this function returns 0, it has succeeded in allocating at least as many
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interrupts as the driver requested (it may have allocated more in order
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to satisfy the power-of-two requirement). In this case, the function
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enables MSI on this device and updates dev->irq to be the lowest of
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the new interrupts assigned to it. The other interrupts assigned to
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the device are in the range dev->irq to dev->irq + count - 1.
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If this function returns a positive number it indicates the number of
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MSI interrupts that have been successfully allocated. In this case
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the device is switched from pin-based interrupt mode to MSI mode and
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updates dev->irq to be the lowest of the new interrupts assigned to it.
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The other interrupts assigned to the device are in the range dev->irq
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to dev->irq + returned value - 1. Device driver can use the returned
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number of successfully allocated MSI interrupts to further allocate
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and initialize device resources.
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If this function returns a negative number, it indicates an error and
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the driver should not attempt to request any more MSI interrupts for
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this device. If this function returns a positive number, it is
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less than 'count' and indicates the number of interrupts that could have
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been allocated. In neither case is the irq value updated or the device
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switched into MSI mode.
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this device.
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The device driver must decide what action to take if
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pci_enable_msi_block() returns a value less than the number requested.
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For instance, the driver could still make use of fewer interrupts;
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in this case the driver should call pci_enable_msi_block()
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again. Note that it is not guaranteed to succeed, even when the
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'count' has been reduced to the value returned from a previous call to
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pci_enable_msi_block(). This is because there are multiple constraints
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on the number of vectors that can be allocated; pci_enable_msi_block()
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returns as soon as it finds any constraint that doesn't allow the
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call to succeed.
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This function should be called before the driver calls request_irq(),
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because MSI interrupts are delivered via vectors that are different
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from the vector of a pin-based interrupt.
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4.2.3 pci_disable_msi
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It is ideal if drivers can cope with a variable number of MSI interrupts;
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there are many reasons why the platform may not be able to provide the
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exact number that a driver asks for.
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There could be devices that can not operate with just any number of MSI
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interrupts within a range. See chapter 4.3.1.3 to get the idea how to
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handle such devices for MSI-X - the same logic applies to MSI.
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4.2.1.1 Maximum possible number of MSI interrupts
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The typical usage of MSI interrupts is to allocate as many vectors as
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possible, likely up to the limit returned by pci_msi_vec_count() function:
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static int foo_driver_enable_msi(struct pci_dev *pdev, int nvec)
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{
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return pci_enable_msi_range(pdev, 1, nvec);
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}
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Note the value of 'minvec' parameter is 1. As 'minvec' is inclusive,
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the value of 0 would be meaningless and could result in error.
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Some devices have a minimal limit on number of MSI interrupts.
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In this case the function could look like this:
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static int foo_driver_enable_msi(struct pci_dev *pdev, int nvec)
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{
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return pci_enable_msi_range(pdev, FOO_DRIVER_MINIMUM_NVEC, nvec);
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}
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4.2.1.2 Exact number of MSI interrupts
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If a driver is unable or unwilling to deal with a variable number of MSI
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interrupts it could request a particular number of interrupts by passing
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that number to pci_enable_msi_range() function as both 'minvec' and 'maxvec'
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parameters:
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static int foo_driver_enable_msi(struct pci_dev *pdev, int nvec)
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{
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return pci_enable_msi_range(pdev, nvec, nvec);
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}
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4.2.1.3 Single MSI mode
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The most notorious example of the request type described above is
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enabling the single MSI mode for a device. It could be done by passing
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two 1s as 'minvec' and 'maxvec':
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static int foo_driver_enable_single_msi(struct pci_dev *pdev)
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{
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return pci_enable_msi_range(pdev, 1, 1);
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}
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4.2.2 pci_disable_msi
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void pci_disable_msi(struct pci_dev *dev)
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This function should be used to undo the effect of pci_enable_msi() or
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pci_enable_msi_block(). Calling it restores dev->irq to the pin-based
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interrupt number and frees the previously allocated message signaled
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interrupt(s). The interrupt may subsequently be assigned to another
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device, so drivers should not cache the value of dev->irq.
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This function should be used to undo the effect of pci_enable_msi_range().
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Calling it restores dev->irq to the pin-based interrupt number and frees
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the previously allocated MSIs. The interrupts may subsequently be assigned
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to another device, so drivers should not cache the value of dev->irq.
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Before calling this function, a device driver must always call free_irq()
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on any interrupt for which it previously called request_irq().
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Failure to do so results in a BUG_ON(), leaving the device with
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MSI enabled and thus leaking its vector.
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4.2.4 pci_msi_vec_count
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4.2.3 pci_msi_vec_count
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int pci_msi_vec_count(struct pci_dev *dev)
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@ -176,26 +206,31 @@ in each element of the array to indicate for which entries the kernel
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should assign interrupts; it is invalid to fill in two entries with the
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same number.
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4.3.1 pci_enable_msix
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4.3.1 pci_enable_msix_range
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int pci_enable_msix(struct pci_dev *dev, struct msix_entry *entries, int nvec)
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int pci_enable_msix_range(struct pci_dev *dev, struct msix_entry *entries,
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int minvec, int maxvec)
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Calling this function asks the PCI subsystem to allocate 'nvec' MSIs.
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Calling this function asks the PCI subsystem to allocate any number of
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MSI-X interrupts within specified range from 'minvec' to 'maxvec'.
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The 'entries' argument is a pointer to an array of msix_entry structs
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which should be at least 'nvec' entries in size. On success, the
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device is switched into MSI-X mode and the function returns 0.
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The 'vector' member in each entry is populated with the interrupt number;
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which should be at least 'maxvec' entries in size.
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On success, the device is switched into MSI-X mode and the function
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returns the number of MSI-X interrupts that have been successfully
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allocated. In this case the 'vector' member in entries numbered from
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0 to the returned value - 1 is populated with the interrupt number;
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the driver should then call request_irq() for each 'vector' that it
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decides to use. The device driver is responsible for keeping track of the
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interrupts assigned to the MSI-X vectors so it can free them again later.
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Device driver can use the returned number of successfully allocated MSI-X
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interrupts to further allocate and initialize device resources.
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If this function returns a negative number, it indicates an error and
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the driver should not attempt to allocate any more MSI-X interrupts for
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this device. If it returns a positive number, it indicates the maximum
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number of interrupt vectors that could have been allocated. See example
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below.
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this device.
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This function, in contrast with pci_enable_msi(), does not adjust
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This function, in contrast with pci_enable_msi_range(), does not adjust
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dev->irq. The device will not generate interrupts for this interrupt
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number once MSI-X is enabled.
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@ -206,28 +241,103 @@ It is ideal if drivers can cope with a variable number of MSI-X interrupts;
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there are many reasons why the platform may not be able to provide the
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exact number that a driver asks for.
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A request loop to achieve that might look like:
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There could be devices that can not operate with just any number of MSI-X
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interrupts within a range. E.g., an network adapter might need let's say
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four vectors per each queue it provides. Therefore, a number of MSI-X
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interrupts allocated should be a multiple of four. In this case interface
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pci_enable_msix_range() can not be used alone to request MSI-X interrupts
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(since it can allocate any number within the range, without any notion of
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the multiple of four) and the device driver should master a custom logic
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to request the required number of MSI-X interrupts.
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4.3.1.1 Maximum possible number of MSI-X interrupts
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The typical usage of MSI-X interrupts is to allocate as many vectors as
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possible, likely up to the limit returned by pci_msix_vec_count() function:
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static int foo_driver_enable_msix(struct foo_adapter *adapter, int nvec)
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{
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while (nvec >= FOO_DRIVER_MINIMUM_NVEC) {
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rc = pci_enable_msix(adapter->pdev,
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adapter->msix_entries, nvec);
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if (rc > 0)
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nvec = rc;
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else
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return rc;
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return pci_enable_msi_range(adapter->pdev, adapter->msix_entries,
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1, nvec);
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}
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Note the value of 'minvec' parameter is 1. As 'minvec' is inclusive,
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the value of 0 would be meaningless and could result in error.
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Some devices have a minimal limit on number of MSI-X interrupts.
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In this case the function could look like this:
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static int foo_driver_enable_msix(struct foo_adapter *adapter, int nvec)
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{
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return pci_enable_msi_range(adapter->pdev, adapter->msix_entries,
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FOO_DRIVER_MINIMUM_NVEC, nvec);
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}
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4.3.1.2 Exact number of MSI-X interrupts
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If a driver is unable or unwilling to deal with a variable number of MSI-X
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interrupts it could request a particular number of interrupts by passing
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that number to pci_enable_msix_range() function as both 'minvec' and 'maxvec'
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parameters:
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static int foo_driver_enable_msix(struct foo_adapter *adapter, int nvec)
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{
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return pci_enable_msi_range(adapter->pdev, adapter->msix_entries,
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nvec, nvec);
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}
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4.3.1.3 Specific requirements to the number of MSI-X interrupts
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As noted above, there could be devices that can not operate with just any
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number of MSI-X interrupts within a range. E.g., let's assume a device that
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is only capable sending the number of MSI-X interrupts which is a power of
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two. A routine that enables MSI-X mode for such device might look like this:
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/*
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* Assume 'minvec' and 'maxvec' are non-zero
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*/
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static int foo_driver_enable_msix(struct foo_adapter *adapter,
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int minvec, int maxvec)
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{
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int rc;
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minvec = roundup_pow_of_two(minvec);
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maxvec = rounddown_pow_of_two(maxvec);
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if (minvec > maxvec)
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return -ERANGE;
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retry:
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rc = pci_enable_msix_range(adapter->pdev, adapter->msix_entries,
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maxvec, maxvec);
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/*
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* -ENOSPC is the only error code allowed to be analized
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*/
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if (rc == -ENOSPC) {
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if (maxvec == 1)
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return -ENOSPC;
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maxvec /= 2;
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if (minvec > maxvec)
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return -ENOSPC;
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goto retry;
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}
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return -ENOSPC;
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return rc;
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}
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Note how pci_enable_msix_range() return value is analized for a fallback -
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any error code other than -ENOSPC indicates a fatal error and should not
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be retried.
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4.3.2 pci_disable_msix
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void pci_disable_msix(struct pci_dev *dev)
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This function should be used to undo the effect of pci_enable_msix(). It frees
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the previously allocated message signaled interrupts. The interrupts may
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This function should be used to undo the effect of pci_enable_msix_range().
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It frees the previously allocated MSI-X interrupts. The interrupts may
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subsequently be assigned to another device, so drivers should not cache
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the value of the 'vector' elements over a call to pci_disable_msix().
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@ -261,13 +371,14 @@ number of MSI-X interrupt vectors that could be allocated.
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If a device implements both MSI and MSI-X capabilities, it can
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run in either MSI mode or MSI-X mode, but not both simultaneously.
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This is a requirement of the PCI spec, and it is enforced by the
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PCI layer. Calling pci_enable_msi() when MSI-X is already enabled or
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pci_enable_msix() when MSI is already enabled results in an error.
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If a device driver wishes to switch between MSI and MSI-X at runtime,
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it must first quiesce the device, then switch it back to pin-interrupt
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mode, before calling pci_enable_msi() or pci_enable_msix() and resuming
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operation. This is not expected to be a common operation but may be
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useful for debugging or testing during development.
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PCI layer. Calling pci_enable_msi_range() when MSI-X is already
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enabled or pci_enable_msix_range() when MSI is already enabled
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results in an error. If a device driver wishes to switch between MSI
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and MSI-X at runtime, it must first quiesce the device, then switch
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it back to pin-interrupt mode, before calling pci_enable_msi_range()
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or pci_enable_msix_range() and resuming operation. This is not expected
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to be a common operation but may be useful for debugging or testing
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during development.
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4.5 Considerations when using MSIs
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@ -382,5 +493,5 @@ or disabled (0). If 0 is found in any of the msi_bus files belonging
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to bridges between the PCI root and the device, MSIs are disabled.
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It is also worth checking the device driver to see whether it supports MSIs.
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For example, it may contain calls to pci_enable_msi(), pci_enable_msix() or
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pci_enable_msi_block().
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For example, it may contain calls to pci_enable_msi_range() or
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pci_enable_msix_range().
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@ -1102,3 +1102,77 @@ void pci_msi_init_pci_dev(struct pci_dev *dev)
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if (dev->msix_cap)
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msix_set_enable(dev, 0);
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}
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/**
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* pci_enable_msi_range - configure device's MSI capability structure
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* @dev: device to configure
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* @minvec: minimal number of interrupts to configure
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* @maxvec: maximum number of interrupts to configure
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*
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* This function tries to allocate a maximum possible number of interrupts in a
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* range between @minvec and @maxvec. It returns a negative errno if an error
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* occurs. If it succeeds, it returns the actual number of interrupts allocated
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* and updates the @dev's irq member to the lowest new interrupt number;
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* the other interrupt numbers allocated to this device are consecutive.
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**/
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int pci_enable_msi_range(struct pci_dev *dev, int minvec, int maxvec)
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{
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int nvec = maxvec;
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int rc;
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if (maxvec < minvec)
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return -ERANGE;
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do {
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rc = pci_enable_msi_block(dev, nvec);
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if (rc < 0) {
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return rc;
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} else if (rc > 0) {
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if (rc < minvec)
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return -ENOSPC;
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nvec = rc;
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}
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} while (rc);
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return nvec;
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}
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EXPORT_SYMBOL(pci_enable_msi_range);
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/**
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* pci_enable_msix_range - configure device's MSI-X capability structure
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* @dev: pointer to the pci_dev data structure of MSI-X device function
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* @entries: pointer to an array of MSI-X entries
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* @minvec: minimum number of MSI-X irqs requested
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* @maxvec: maximum number of MSI-X irqs requested
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*
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* Setup the MSI-X capability structure of device function with a maximum
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* possible number of interrupts in the range between @minvec and @maxvec
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* upon its software driver call to request for MSI-X mode enabled on its
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* hardware device function. It returns a negative errno if an error occurs.
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* If it succeeds, it returns the actual number of interrupts allocated and
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* indicates the successful configuration of MSI-X capability structure
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* with new allocated MSI-X interrupts.
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**/
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int pci_enable_msix_range(struct pci_dev *dev, struct msix_entry *entries,
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int minvec, int maxvec)
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{
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int nvec = maxvec;
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int rc;
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if (maxvec < minvec)
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return -ERANGE;
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do {
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rc = pci_enable_msix(dev, entries, nvec);
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if (rc < 0) {
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return rc;
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} else if (rc > 0) {
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if (rc < minvec)
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return -ENOSPC;
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nvec = rc;
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}
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} while (rc);
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return nvec;
|
||||
}
|
||||
EXPORT_SYMBOL(pci_enable_msix_range);
|
||||
|
||||
@ -1193,6 +1193,17 @@ static inline int pci_msi_enabled(void)
|
||||
{
|
||||
return 0;
|
||||
}
|
||||
|
||||
static inline int pci_enable_msi_range(struct pci_dev *dev, int minvec,
|
||||
int maxvec)
|
||||
{
|
||||
return -ENOSYS;
|
||||
}
|
||||
static inline int pci_enable_msix_range(struct pci_dev *dev,
|
||||
struct msix_entry *entries, int minvec, int maxvec)
|
||||
{
|
||||
return -ENOSYS;
|
||||
}
|
||||
#else
|
||||
int pci_msi_vec_count(struct pci_dev *dev);
|
||||
int pci_enable_msi_block(struct pci_dev *dev, int nvec);
|
||||
@ -1205,6 +1216,9 @@ void pci_disable_msix(struct pci_dev *dev);
|
||||
void msi_remove_pci_irq_vectors(struct pci_dev *dev);
|
||||
void pci_restore_msi_state(struct pci_dev *dev);
|
||||
int pci_msi_enabled(void);
|
||||
int pci_enable_msi_range(struct pci_dev *dev, int minvec, int maxvec);
|
||||
int pci_enable_msix_range(struct pci_dev *dev, struct msix_entry *entries,
|
||||
int minvec, int maxvec);
|
||||
#endif
|
||||
|
||||
#ifdef CONFIG_PCIEPORTBUS
|
||||
|
||||
Loading…
Reference in New Issue
Block a user