On 30 October 2017 at 03:52, Heyi Guo <heyi....@linaro.org> wrote: > Hi folks, > > In NonDiscoverablePciDeviceDxe driver, NonCoherentPciIoAllocateBuffer may > allocate EFI_MEMORY_UC buffer depending on input Attributes and GCD > capabilities. If it does, it actually allocates memory of "device" type in > AArch64, but not "normal uncacheable" memory. For "device" memory type, it > requires restrict access alignment and it may trigger alignment fault > exception with BaseMemoryLibOptDxe in which read/write alignment is not > guaranteed. > > Is EFI_MOMORY_WC enough for AArch64 platforms? How about other platforms, > like X86? >
Hello Heyi, Do you mean EFI_MEMORY_UC in the last sentence? If not, I don't understand the question. Anyway, in reality, this code will only allocate EFI_MEMORY_UC memory if any memory already exists in the memory map with that capability, otherwise it will fall back to EFI_MEMORY_WC. On most arm64 platforms, we no longer add this capability to system memory by default, so you should be getting EFI_MEMORY_WC in most cases. So the question is actually the opposite: does this interfere with correct operation in cases where the shared mapping between the CPU and the device should be strongly ordered, and EFI_MEMORY_WC doesn't give sufficient guarantees. -- Ard. _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
