Re: [PATCH 3/4] arm64: dts: qcom: sdm845: Add missing MDSS reset

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 4/9/26 11:24 PM, Dmitry Baryshkov wrote:
> On Thu, Apr 09, 2026 at 10:38:15PM +0200, David Heidelberg wrote:
>> On 18/02/2026 16:59, Dmitry Baryshkov wrote:
>>> On Wed, Feb 18, 2026 at 03:28:01PM +0100, Konrad Dybcio wrote:
>>>>
>>>>
>>>> On 18-Feb-26 12:58, Dmitry Baryshkov wrote:
>>>>> On Wed, Feb 18, 2026 at 12:24:26PM +0100, Konrad Dybcio wrote:
>>>>>> On 2/18/26 12:18 PM, David Heidelberg wrote:
>>>>>>> On 18/02/2026 11:30, Konrad Dybcio wrote:
>>>>>>>> On 2/17/26 10:20 PM, Dmitry Baryshkov wrote:
>>>>>>>>> From: David Heidelberg <david@ixit.cz>
>>>>>>>>>
>>>>>>>>> If the OS does not support recovering the state left by the
>>>>>>>>> bootloader it needs a way to reset display hardware, so that it can
>>>>>>>>> start from a clean state. Add a reference to the relevant reset.
>>>>>>>>
>>>>>>>> This is not the relevant reset
>>>>>>>>
>>>>>>>> You want MDSS_CORE_BCR @ 0xaf0_2000
>>>>>>>
>>>>>>> Thanks, I prepared the fixes [1].
>>>>>>>
>>>>>>> I'll try to test it if it's not breaking anything for us and send as v2 of [2].
>>>>>>>
>>>>>>> David
>>>>>>>
>>>>>>> [1] https://codeberg.org/sdm845/linux/commits/branch/b4/mdss-reset
>>>>>>> [2] https://patchwork.kernel.org/project/linux-arm-msm/patch/20260112-mdss-reset-v1-1-af7c572204d3@ixit.cz/
>>>>>>
>>>>>> Please don't alter the contents of dt-bindings, it really doesn't matter
>>>>>> if on sdm845 it's reset0 or reset1, that's why we define them in the first
>>>>>> place
>>>>>
>>>>> I dpn't think that will pass. Current reset is defined as RSCC, we can't
>>>>> change that to CORE behind the scene. I'd prefer David's approach.
>>>>
>>>> Back when I replied, David had a patch that removed the current RSCC
>>>> reset definition in dt-bindings (at index 0) and re-used that index
>>>> for CORE, putting RSCC at index 1. Perhaps it's better to link to
>>>> specific commits when making comments, note to self :P
>>>
>>> Yes, I saw the commit having two resets. Anyway, as we saw, it doesn't
>>> work.
>>
>> So, finally I spent "so much effort" (read throwing it at LLM) looking at:
>>
>> arm-smmu 15000000.iommu: Unhandled context fault: fsr=0x402,
>> iova=0x9d4bb500, fsynr=0x170021, cbfrsynra=0xc88, cb=11
>> arm-smmu 15000000.iommu: FSR    = 00000402 [Format=2 TF], SID=0xc88
>> arm-smmu 15000000.iommu: FSYNR0 = 00170021 [S1CBNDX=23 PNU PLVL=1]
> 
> [...]
> 
>>
>> These (or very similar warnings) are around sdm845 definitely 6.19+ /
>> linux-next kernels for some time, but pretty harmless.
>>
>> LLM suggested multiple fixes, but when presenting possibility of
>> implementing mdss reset it found it as most preferable [1].
>>
>> Adding MDSS reset would most likely solve it. It's not critical, but not
>> nice to see many red lines in the dmesg.
>>
>> Is there something I could experiment with to get closer to have proper MDSS reset?
> 
> I don't have a sensible solution at this point. We tried using the MDSS
> reset on several SDM845 devices, but they just reset. So... I don't have
> any possible solution.

The older context talks about altering the existing dt-bindings values
and now we're at hardware (mis)behaving? What is the issue here?

Konrad