On Mon, Jul 15, 2013 at 4:20 PM, Josh Triplett <josh@xxxxxxxxxxxxxxxx> wrote: > On Mon, Jul 15, 2013 at 04:08:13PM -0700, Andy Lutomirski wrote: >> On Mon, Jul 15, 2013 at 4:04 PM, Josh Triplett <josh@xxxxxxxxxxxxxxxx> wrote: >> > On Mon, Jul 15, 2013 at 01:28:36PM -0700, Andy Lutomirski wrote: >> >> >> >> Interesting. My BGRT says: >> >> >> >> [028h 0040 8] Image Address : 0D06801800000001 >> >> >> >> If I reverse the high and low 32-bit dwords, then I get an address in >> >> system RAM. >> > >> > Does that address in RAM start with a BMP header? >> >> No idea. I'd presumably have to modify the driver to find out -- >> otherwise something else will overwrite it. > > You could boot with a mem= command-line argument that reserves that > memory. I'll see what I can do. > >> > Because that would be *special*. I don't think it's worth trying to >> > cope with that bug; better to just write off the BGRT as invalid if the >> > BIOS can't get endianness right. >> > >> > In theory we could guess at that bug if the unmangled address points to >> > a location in RAM starting with a BMP header. In practice, let's not; a >> > missing BGRT is a purely cosmetic issue, and BIOS vendors can learn to >> > get that one right if they want to see their logo during Linux boot. >> > This won't break fastboot support, it just breaks fancy crossfades from >> > the BIOS logo to a Linux desktop or splash. >> >> FWIW, the address that my BIOS gives is non-canonical. Maybe that's >> good enough. > > What do you mean by "non-canonical". Brainfart. I'm confusing physical and virtual addresses. More usefully, the bogus address from my BIOS is too large -- it's way above the highest e820 spot (and I'm pretty sure it exceeds the maximum address that my CPU can address). Maybe that would be a decent heuristic to use to avoid trying to follow the pointer. > >> > So, a "firmware bug" message in dmesg seems sufficent for that case. We >> > do need to handle the case of a valid pointer into memory that e820 >> > calls system RAM, as well as the case of a valid pointer into memory >> > reserved for the BIOS or similar, but not the case of an invalid >> > pointer. >> >> Is the efi_bgrt code called early enough that data in system RAM will >> still be there? > > In theory, it should always point to data in EFI's "reserved until after > boot time" memory. > > - Josh Triplett -- 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
