[PATCH 4/9] drm/panfrost: Handle HW_ISSUE_TTRX_3076

[Steven Price]

On 14/02/2022 17:06, Alyssa Rosenzweig wrote:
> On Mon, Feb 14, 2022 at 04:23:18PM +0000, Steven Price wrote:
>> On 11/02/2022 20:27, alyssa.rosenzweig at collabora.com wrote:
>>> From: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
>>>
>>> Some Valhall GPUs require resets when encountering bus faults due to
>>> occlusion query writes. Add the issue bit for this and handle it.
>>>
>>> Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
>>
>> Reviewed-by: Steven Price <steven.price at arm.com>
>> (although one nit below)
>>
>> Just in case any one is wondering - these bus faults occur when
>> switching the GPU's MMU to unmapped - it's not a normal "bus fault" from
>> the external bus. This is triggered by an attempt to read unmapped
>> memory which is completed by the driver by switching the entire MMU to
>> unmapped.
> 
> Ouch, that's subtle.
> 
>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_issues.h b/drivers/gpu/drm/panfrost/panfrost_issues.h
>>> index a66692663833..058f6a4c8435 100644
>>> --- a/drivers/gpu/drm/panfrost/panfrost_issues.h
>>> +++ b/drivers/gpu/drm/panfrost/panfrost_issues.h
>>> @@ -128,6 +128,10 @@ enum panfrost_hw_issue {
>>>  	/* Must set SC_VAR_ALGORITHM */
>>>  	HW_ISSUE_TTRX_2968_TTRX_3162,
>>>  
>>> +	/* Bus fault from occlusion query write may cause future fragment jobs
>>> +	 * to hang */
>>
>> NIT: Kernel comment style has the "/*" and "*/" on lines by themselves
>> for multi-line comments. checkpatch will complain!
> 
> Yes, I am aware (and checkpatch did complain). The existing multi-line
> comments in that file do not have the extra lines. Consistency within
> the file seemed like the lesser evil. If you think it's better to
> appease checkpatch, I can reformat for v2.
> 
> (I can also throw in a patch fixing the rest of that file's multiline
> comments but that seems a bit extra.)

Nah! I've never been very keen on that style rule myself, but I usually
try to keep checkpatch happy when working on the kernel. Lets just
follow the rest of the file for now.

Thanks,

Steve