Re: [PATCH] drm/amdgpu/gmc_v8_0: restore the FB location after a re-POST

["Francisco Beltrán Millalén" <fbeltranmillalen@gmail.com>]

On Thu, Sep 24, 2026 at 11:21 AM Alex Deucher <alexdeucher@gmail.com> wrote:
> On Thu, Sep 24, 2026 at 11:06 AM Christian König
> <christian.koenig@amd.com> wrote:
>> On 9/24/26 15:29, Francisco Beltrán Millalén wrote:
>>>   cold boot:   MC_VM_FB_LOCATION = 0x007f0000
>>>   after reset: MC_VM_FB_LOCATION = 0xf47ff400
>>
>> Mhm, interesting I'm really wondering where those values come from.

0x007f0000 is what amdgpu finds when it loads after a cold boot, with
HDP_NONSURFACE_BASE = 0: the framebuffer at MC address 0.  That is what
the platform hands over; I have no trace of who writes it before the
kernel runs, so I can only say it comes from the Apple side.

0xf47ff400, with HDP_NONSURFACE_BASE = 0xf4000000, is written by the
VBIOS ASIC_Init table that amdgpu runs on resume and after a GPU reset.
I traced the register writes across that call.  As far as I know it
is the usual 0xF4_0000_0000 placement of Polaris boards elsewhere.
(The "0xf400_0000" in my commit message was wrong: the MC address is
0xF4_0000_0000.)

>> I think the more defensive approach is to do an ASIC reset on driver
>> load and use the values the AtomBIOS init function comes up with.
[...]
> I agree that running asic_init
> on boot for Macs would make sense.  I think we already have a similar
> workaround for some other mac models, probably to work around a
> similar issue:
> https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a5be7ad8f5f0e067613e9197638f216f46252946
> Maybe add your device to that existing quirk or make the quirk generic
> for all VI boards with apple ssids?

That works, thank you both.  I backported a5be7ad8f5f0 to 6.18.49,
added this board (106b:017a rev c7) and dropped my gmc_v8_0 patch:

- On load: "PCI CONFIG reset", "GPU posting now...", then
  "VRAM: 2048M 0x000000F400000000 - 0x000000F47FFFFFFF", after both a
  cold and a warm boot.  With a debug print just before the reset,
  MC_VM_FB_LOCATION reads 0x007f0000 before it and 0xf47ff400 after.

- S3: 9 suspend/resume cycles (lid close and rtcwake, one of them with
  the lid closed for about 7.5 minutes and a USB-C disk attached), each
  followed by a few minutes of 3D load.  MC_VM_FB_LOCATION stays at
  0xf47ff400 and no ring timeouts or VM faults were reported.  In 4 of
  them my old patch was still in as a detector and never fired; the
  other 5 ran without it.  The kernel also carries my unrelated PCI and
  ACPI patches for this machine.

- Cost: the reset and post take 20-35 ms, and amdgpu init up to fbdev
  takes about 0.23 s longer than before.

So please consider the gmc_v8_0 patch withdrawn.  I'll send the one-line
quirk as v2 in reply to this thread.

Two things in case you prefer the generic version:

- The GPU here is a Radeon Pro 555 (2 GB), not the 560 I wrote.  The
  MacBookPro14,3 was also sold with a Pro 560.  pci.ids lists 106b:0179
  as a Radeon Pro 560 and 106b:0160, 0166 and 0167 as the Pro 460, 455
  and 450 (the GPUs of the 2016 MacBookPro13,3), all 1002:67ef.  I have
  not checked those IDs on real machines, and I only have this one, so
  I only added 017a/c7.

- From reading the code, on VI the reset on load is always a PCI
  config reset: the BACO capability is only known once the PowerPlay
  table is parsed in hw_init, after the reset.  That is also what
  happens here.

Thanks,
Francisco