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qdev: Support marking individual buses as 'full'

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By default, QEMU will allow devices to be plugged into a bus up to
the bus class's device count limit.  If the user creates a device on
the command line or via the monitor and doesn't explicitly specify
the bus to plug it in, QEMU will plug it into the first non-full bus
that it finds.

This is fine in most cases, but some machines have multiple buses of
a given type, some of which are dedicated to on-board devices and
some of which have an externally exposed connector for user-pluggable
devices. One example is I2C buses.

Provide a new function qbus_mark_full() so that a machine model can
mark this kind of "internal only" bus as 'full' after it has created
all the devices that should be plugged into that bus. The "find a
non-full bus" algorithm will then skip the internal-only bus when
looking for a place to plug in user-created devices.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210903151435.22379-2-peter.maydell@linaro.org
This commit is contained in:
Peter Maydell 2021-09-13 16:07:25 +01:00
parent bc7edccae0
commit 1518562b49
2 changed files with 30 additions and 1 deletions
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24
include/hw/qdev-core.h
View File

@ -264,6 +264,7 @@ struct BusState {
HotplugHandler *hotplug_handler;
int max_index;
bool realized;
bool full;
int num_children;
/*
@ -798,6 +799,29 @@ static inline bool qbus_is_hotpluggable(BusState *bus)
return bus->hotplug_handler;
}
/**
* qbus_mark_full: Mark this bus as full, so no more devices can be attached
* @bus: Bus to mark as full
*
* By default, QEMU will allow devices to be plugged into a bus up
* to the bus class's device count limit. Calling this function
* marks a particular bus as full, so that no more devices can be
* plugged into it. In particular this means that the bus will not
* be considered as a candidate for plugging in devices created by
* the user on the commandline or via the monitor.
* If a machine has multiple buses of a given type, such as I2C,
* where some of those buses in the real hardware are used only for
* internal devices and some are exposed via expansion ports, you
* can use this function to mark the internal-only buses as full
* after you have created all their internal devices. Then user
* created devices will appear on the expansion-port bus where
* guest software expects them.
*/
static inline void qbus_mark_full(BusState *bus)
{
bus->full = true;
}
void device_listener_register(DeviceListener *listener);
void device_listener_unregister(DeviceListener *listener);

7
softmmu/qdev-monitor.c
View File

@ -435,7 +435,12 @@ static DeviceState *qbus_find_dev(BusState *bus, char *elem)
static inline bool qbus_is_full(BusState *bus)
{
BusClass *bus_class = BUS_GET_CLASS(bus);
BusClass *bus_class;
if (bus->full) {
return true;
}
bus_class = BUS_GET_CLASS(bus);
return bus_class->max_dev && bus->num_children >= bus_class->max_dev;
}