[PATCH v2 1/2] drm/msm/dp: Disable wide bus support for SDM845

[Dmitry Baryshkov]

On Thu, Feb 13, 2025 at 12:41:02AM +0100, Marijn Suijten wrote:
> On 2025-02-12 15:03:46, James A. MacInnes wrote:
> > SDM845 DPU hardware is rev 4.0.0 per hardware documents.
> > Original patch to enable wide_bus operation did not take into account
> > the SDM845 and it got carried over by accident.
> > 
> > - Incorrect setting caused inoperable DisplayPort.
> > - Corrected by separating SDM845 into its own descriptor.
> 
> If anything I'd have appreciated to see our conversation in v1 pasted here
> verbatim which is of the right verbosity to explain this.  I can't do much with
> a list of two items.
> 
> I don't have a clearer way of explaining what all I find confusing about this
> description, so let me propose what I would have written if this was my patch
> instead:
> 
> 	When widebus was enabled for DisplayPort in commit c7c412202623 ("drm/msm/dp:
> 	enable widebus on all relevant chipsets") it was clarified that it is only
> 	supported on DPU 5.0.0 onwards which includes SC7180 on DPU revision 6.2.
> 	However, this patch missed that the description structure for SC7180 is also
> 	reused for SDM845 (because of identical io_start address) which is only DPU
> 	4.0.0, leading to a wrongly enbled widebus feature and corruption on that
> 	platform.
> 
> 	Create a separate msm_dp_desc_sdm845 structure for this SoC compatible,
> 	with the wide_bus_supported flag turned off.
> 
> 	Note that no other DisplayPort compatibles currently exist for SoCs older
> 	than DPU 4.0.0 besides SDM845.

With more or less similar commit message:


Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>


> 
> Hope I'm not considered being too picky.  I first sketch **how** the original
> patch created a problem, then explain how this patch is intending to fix it,
> and finally describe that we went a step further and ensured no other SoCs
> are suffering from a similar problem.
> 
> - Marijn
> 
> > 
> > Fixes: c7c412202623 ("drm/msm/dp: enable widebus on all relevant chipsets")
> > Signed-off-by: James A. MacInnes <james.a.macinnes at gmail.com>
> > ---
> >  drivers/gpu/drm/msm/dp/dp_display.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> > index aff51bb973eb..e30cccd63910 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_display.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> > @@ -126,6 +126,11 @@ static const struct msm_dp_desc msm_dp_desc_sa8775p[] = {
> >  	{}
> >  };
> >  
> > +static const struct msm_dp_desc msm_dp_desc_sdm845[] = {
> > +	{ .io_start = 0x0ae90000, .id = MSM_DP_CONTROLLER_0 },
> > +	{}
> > +};
> > +
> >  static const struct msm_dp_desc msm_dp_desc_sc7180[] = {
> >  	{ .io_start = 0x0ae90000, .id = MSM_DP_CONTROLLER_0, .wide_bus_supported = true },
> >  	{}
> > @@ -178,7 +183,7 @@ static const struct of_device_id msm_dp_dt_match[] = {
> >  	{ .compatible = "qcom,sc8180x-edp", .data = &msm_dp_desc_sc8180x },
> >  	{ .compatible = "qcom,sc8280xp-dp", .data = &msm_dp_desc_sc8280xp },
> >  	{ .compatible = "qcom,sc8280xp-edp", .data = &msm_dp_desc_sc8280xp },
> > -	{ .compatible = "qcom,sdm845-dp", .data = &msm_dp_desc_sc7180 },
> > +	{ .compatible = "qcom,sdm845-dp", .data = &msm_dp_desc_sdm845 },
> >  	{ .compatible = "qcom,sm8350-dp", .data = &msm_dp_desc_sc7180 },
> >  	{ .compatible = "qcom,sm8650-dp", .data = &msm_dp_desc_sm8650 },
> >  	{ .compatible = "qcom,x1e80100-dp", .data = &msm_dp_desc_x1e80100 },
> > 
> > -- 
> > 2.43.0
> > 

-- 
With best wishes
Dmitry