Re: [PATCH v4] drm/amd/pm: defer UCLK DPM on selected Apple Navi GPUs

[Aditya Garg <aditya.garg@linux.dev>]

> On 4 Nov 2026, at 7:37 PM, Alex Deucher <alexdeucher@gmail.com> wrote:
> 
> On Wed, Nov 4, 2026 at 7:52 AM Ed Schofield <ed@charmerstraining.com> wrote:
>> 
>> Hi Alex, hi Atharva, hi all,
>> 
>> Alex, I'd like to withdraw my September v4 submission. I also don't support
>> applying v5 as posted or the simplified patch you attached later in this
>> thread. Please remove my Co-developed-by and Signed-off-by tags from both
>> versions. I no longer think deferring UCLK is the right approach for the iMacs.
>> 
>> I also excluded the MacBookPro16,1 (020f) from v4 deliberately because a tester
>> found that with deferred UCLK it still hung after login, as it does without the
>> patch [1], which seems to fit André's PPTable diagnosis.
>> 
>> Since then, I've been working with Atharva to get his native-5K iMac support
>> upstream. His patch initializes the display before the SMU, which has also
>> prevented the boot failures without deferring UCLK. On my iMac20,1 (0218), 13
>> of 20 warm boots failed with the upstream order; with display first, all 40
>> boots passed [4]. Another tester reported one warm and one cold boot, both
>> successful, on a 0219 [2]. On an iMac20,2 (021a), changing only the
>> initialization order improved warm boot success from 11 out of 20 to 100 out of
>> 100 [3]. His patch only applies to the iMac20,1 and iMac20,2, so it doesn't fix
>> the 16,1 either.
>> 
>> I don't think the iMacs and the MacBookPro16,1 have the same problem. The
>> iMacs fail while amdgpu is loading: the SMU stops responding to
>> EnableAllSmuFeatures (message 6), and the probe fails with -62. With the
>> display initialized first, the same message succeeds with UCLK included,
>> and the iMac boots normally. The 16,1 loads amdgpu without errors and hangs
>> later, after login, with or without deferred UCLK [1]. So deferring UCLK
>> seems to help the iMacs only because it moves the enable after display
>> init, and it doesn't help the MacBookPro16,1.
>> 
>> I have prepared a draft patch with Atharva as author and me as co-developer,
>> incorporating his review feedback. It combines display-first initialization and
>> native 5120x2880 support through two tiled connectors with suspend/resume and
>> display power-management changes. The current draft is here:
>> 
>> https://github.com/edschofield/linux-t2-patches/blob/7273823e425200e9f371e9272e02ebf9abb6f1c2/7003-amdgpu-add-support-for-5K.patch
>> 
>> This has passed some initial automated testing on my iMac20,1 but I need to do
>> more testing and get Atharva's final review and sign-off.
> 
> There are already patches on the list to support the 5K Macs:
> https://lists.freedesktop.org/archives/dri-devel/2026-November/610011.html

Those patches are for older non T2 iMacs. We are discussing iMac20,1 and 20,2 which are T2 Macs.
> 
> Alex
> 
>> 
>> Alex, thanks for following up on the boot issue and checking with the Windows
>> team.
>> 
>> Best regards,
>> Ed
>> 
>> [1] https://github.com/t2linux/linux-t2-patches/pull/61#issuecomment-5646139127
>> [2] https://github.com/t2linux/wiki/issues/743#issuecomment-6083265811
>> [3] https://github.com/t2linux/wiki/issues/743#issuecomment-6131809640
>> [4] https://github.com/t2linux/wiki/issues/743#issuecomment-6163146905