linux-kernel - Re: [PATCH 05/17] drm/msm/a6xx: Fix PDC sleep sequence

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Message-ID: <5e862a36-8384-4098-b22a-9bbad1205965@oss.qualcomm.com>
Date: Thu, 14 Aug 2025 02:45:41 +0530
From: Akhil P Oommen <akhilpo@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Rob Clark <robin.clark@....qualcomm.com>, Sean Paul <sean@...rly.run>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jessica.zhang@....qualcomm.com>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/17] drm/msm/a6xx: Fix PDC sleep sequence

On 8/11/2025 2:10 PM, Konrad Dybcio wrote:
> On 8/8/25 7:22 PM, Akhil P Oommen wrote:
>> On 8/7/2025 7:21 PM, Konrad Dybcio wrote:
>>> On 7/20/25 2:16 PM, Akhil P Oommen wrote:
>>>> Since the PDC resides out of the GPU subsystem and cannot be reset in
>>>> case it enters bad state, utmost care must be taken to trigger the PDC
>>>> wake/sleep routines in the correct order.
>>>>
>>>> The PDC wake sequence can be exercised only after a PDC sleep sequence.
>>>> Additionally, GMU firmware should initialize a few registers before the
>>>> KMD can trigger a PDC sleep sequence. So PDC sleep can't be done if the
>>>> GMU firmware has not initialized. Track these dependencies using a new
>>>> status variable and trigger PDC sleep/wake sequences appropriately.
>>>>
>>>> Signed-off-by: Akhil P Oommen <akhilpo@....qualcomm.com>
>>>> ---
>>>
>>> FWIW some time ago I made this patch, which tackles a similar issue,
>>> perhaps it's a good idea to merge both:
>>>
>>> From 7d6441fc6ec5ee7fe723e1ad86d11fdd17bee922 Mon Sep 17 00:00:00 2001
>>> From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
>>> Date: Thu, 20 Feb 2025 10:28:51 +0100
>>> Subject: [PATCH] drm/msm/adreno: Delay the Adreno RPMh startup to HFI init
>>>
>>> There's no use in trying to power up the GX logic before we're almost
>>> ready to fire up the GPU. In fact, with A8xx the PDC and RSC uCode are
>>> loaded by the GMU firmware, so we *must* wait for the GMU to fully
>>> initialize before trying to do so.
>>>
>>
>> iirc, this wake up sequence should be done before fw start. That aligns
>> with downstream sequence order too.
> 
> FWIW techpack/graphics adreno_gen7_gmu.c @ gfx-kernel.lnx.15.0.r3-rel
> adb0a9da173e ("kgsl: rgmu: corrected pm suspend flag check on resume")
> 
> // load gmu fw, enable clocks, irq, set up chipid etc.
> [...]
> 
> // unmask CM3_SYSRESET
> ret = gen7_gmu_device_start(adreno_dev);
> if (ret)
>         goto err;
> 
> if (!test_bit(GMU_PRIV_PDC_RSC_LOADED, &gmu->flags)) {
> 	// set PDC_GPU_ENABLE_PDC & seq_start_addr
>         ret = gen7_load_pdc_ucode(adreno_dev);
>         if (ret)
>                 goto err;
> 
> 	// disable hwcg, sleep/wake handshake setup, pdc ucode
>         gen7_load_rsc_ucode(adreno_dev);
>         set_bit(GMU_PRIV_PDC_RSC_LOADED, &gmu->flags);
> }
> 
> // set HFI_CTRL_INIT
> ret = gen7_gmu_hfi_start(adreno_dev);
> if (ret)
>         goto err;
> 
> // continue booting the gpus, send out feature messages
> 
> on a830, the patch is observably necessary (gmu doesn't start otherwise)

I am confused actually, why are we mixing ucode load and PDC trigger
sequence?

-Akhil.

> 
> Konrad