KVM guests on ARM have special requirements when it comes to mapping framebuffers: given that the host [emulating the framebuffer] uses cacheable accesses to read from the framebuffer region, the guest should uses cacheable accesses as well, or coherency is lost, i.e., the host does not see what the guest writes. Modifying PCI drivers to take this into account just for KVM on ARM is unreasonable, given that mapping BARs cacheable and still expecting side effects does not make any sense. However, doing the same for regions of system memory does make sense, since a framebuffer in DRAM could be accessed via DMA by a coherent master, and so it makes sense to take the memory attributes described by the UEFI memory map into account if it covers the efifb region. Patch #2 implements this. Patch #1 is a preparatory patch that makes efi_mem_desc_lookup() usable for us in #2. Question is how to best test this. I tried Gerd's ramfb patches against QEMU with a recent ArmVirtQemu build but I am having trouble getting my console to use the EFI framebuffer. Ard Biesheuvel (2): efi: drop type and attribute checks in efi_mem_desc_lookup() fbdev/efifb: honour UEFI memory map attributes when mapping the fb arch/x86/platform/efi/quirks.c | 3 +- drivers/firmware/efi/efi.c | 8 +-- drivers/firmware/efi/esrt.c | 5 +- drivers/video/fbdev/efifb.c | 52 ++++++++++++++++---- 4 files changed, 49 insertions(+), 19 deletions(-) -- 2.17.1 -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
