On Jul 16, 2013 6:55 PM, "Andy Lutomirski" <[email protected]> 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.
Parag