linux-kernel - Re: [PATCH] drm/msm: adreno: fix deferencing ifpc

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Message-ID: <a874d12a-6da4-4a2a-bea3-20c69bd53c6b@oss.qualcomm.com>
Date: Tue, 18 Nov 2025 13:17:03 +0530
From: Akhil P Oommen <akhilpo@....qualcomm.com>
To: Neil Armstrong <neil.armstrong@...aro.org>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: 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>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm: adreno: fix deferencing ifpc_reglist when not
 declared

On 11/17/2025 9:17 PM, Neil Armstrong wrote:
> On 11/17/25 16:02, Konrad Dybcio wrote:
>> On 11/17/25 3:51 PM, Neil Armstrong wrote:
>>> On plaforms with an a7xx GPU not supporting IFPC, the ifpc_reglist
>>> if still deferenced in a7xx_patch_pwrup_reglist() which causes
>>> a kernel crash:
>>> Unable to handle kernel NULL pointer dereference at virtual address
>>> 0000000000000008
>>> ...
>>> pc : a6xx_hw_init+0x155c/0x1e4c [msm]
>>> lr : a6xx_hw_init+0x9a8/0x1e4c [msm]
>>> ...
>>> Call trace:
>>>    a6xx_hw_init+0x155c/0x1e4c [msm] (P)
>>>    msm_gpu_hw_init+0x58/0x88 [msm]
>>>    adreno_load_gpu+0x94/0x1fc [msm]
>>>    msm_open+0xe4/0xf4 [msm]
>>>    drm_file_alloc+0x1a0/0x2e4 [drm]
>>>    drm_client_init+0x7c/0x104 [drm]
>>>    drm_fbdev_client_setup+0x94/0xcf0 [drm_client_lib]
>>>    drm_client_setup+0xb4/0xd8 [drm_client_lib]
>>>    msm_drm_kms_post_init+0x2c/0x3c [msm]
>>>    msm_drm_init+0x1a4/0x228 [msm]
>>>    msm_drm_bind+0x30/0x3c [msm]
>>> ...
>>>
>>> Check the validity of ifpc_reglist before deferencing the table
>>> to setup the register values.
>>>
>>> Fixes: a6a0157cc68e ("drm/msm/a6xx: Enable IFPC on Adreno X1-85")
>>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
>>> ---
>>
>> I think it should be fine to skip calling this func altogether
>> if !ifpc || !pwrup_reglist
>>
>> Although ifpc && !pwrup_reglist should probably scream very loud

That's correct. It is a weird combo.

> 
> Sorry but why? pwrup_reglist was introduced way earlier than IFPC.

Pwrup list is shared with preemption feature too. And preemption support
was introduced before IFPC.

nit: It is nice to have a similar NULL check for pwrup reglist too. We
sometimes skip these during initial GPU bringup (like A840 for eg:).

-Akhil

> 
> Why would we be skipping the a7xx_patch_pwrup_reglist() because
> ifpc_reglist is not declared ???
> 
> Neil
> 
>>
>> Konrad
>