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

[Dmitry Baryshkov]

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@xxxxxxx>
> > > > > > > > 
> > > > > > > > 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@xxxxxxx/
> > > > > 
> > > > > 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.

> 
> David
> 
> [1] https://paste.sr.ht/~okias/c20e8bb1a67ba09df558d56da84894d71ddc1b54

-- 
With best wishes
Dmitry