On Tue, Jul 16, 2013 at 4:23 PM, Parag Warudkar <parag.lkml@xxxxxxxxx> wrote: > > On Jul 16, 2013 6:55 PM, "Andy Lutomirski" <luto@xxxxxxxxxxxxxx> wrote: > >> > Ok, so I played around with it a bit and the following patch works >> > fine on my system. (I.E. image size is reasonable, cat >> > /sys/firmware/acpi/bgrt/image > img.bmp generates a valid, >> > non-distorted bitmap, which it did before too, btw as despite of the >> > ioremap WARN_ON the ioremap seems to succeed if !(is_ram && >> > pfn_valid(pfn) && !PageReserved.) >> > >> >> How reliable is this? That is, is there any guarantee that nothing >> will have overwritten the image in memory before this code runs? >> > From the little digging I did, this code runs fairly early in the boot > process, right after ACPI acquires all tables. If I am not mistaken it runs > as part of efi_late_init which should be before efi_free_boot_services() is > called. > > Image address on my system is 00000000B2E1B018. At boot EFI prints the > following - > > [ 0.000000] efi: mem23: type=4, attr=0xf, > range=[0x00000000b2c34000-0x00000000b2e5d0 > > Type=4, again if I am not mistaken is EFI_BOOT_SERVICES_DATA. So all put > together I think it should be reliable to read off of that address when > efi-bgrt-init runs, which is before the boot services code and data are > discarded. Fair enough. I leave it to the experts to comment on whether there should be some explicit check of whether this is EFI_BOOT_SERVICES_DATA. FWIW, if my board does indeed have a DWORD-swapped address, it's in plain old RAM (type=7). --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
