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Linux kernel source tree
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Some Host Controller hardware blocks, like the OHCI, EHCI and SDIO controllers, have hardware blocks that are not capable of doing 64 bit DMA. These host controllers fail on boards with >3GB of memory because the memory above 3GB is located physically >= 0x100000000 and can only be accessed using 64 DMA. The way Linux is currently configured for BRCMSTB systems, the memory given to drivers for DMA through functions like dma_alloc_coherent() comes from CMA memory and CMA memory is taken from the top of physical memory. When these drivers get a DMA buffer with an address >=0x100000000, they end up dropping the upper 32 bit of the address causing the hardware to DMA to incorrect memory, typically BMEM (custom memory carveout). This issue was discovered on a BCM97449SSV_DDR4 system with 4GB or memory. The fix is to enable CONFIG_ZONE_DMA. On ARM systems this makes sure that all DMA memory is located within the first 32 bits of address space. Signed-off-by: Al Cooper <alcooperx@gmail.com> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.