Re: [PATCH 1/2] Revert "drm/i915/dp: Reject HBR3 when sink doesn't support TPS4"

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Jun 24, 2025 at 10:10:53AM +0530, Nautiyal, Ankit K wrote:
> 
> On 6/23/2025 8:12 PM, Ville Syrjälä wrote:
> > On Fri, Jun 20, 2025 at 06:14:16PM +0530, Ankit Nautiyal wrote:
> >> This reverts commit 584cf613c24a4250d9be4819efc841aa2624d5b6.
> >> Commit 584cf613c24a ("drm/i915/dp: Reject HBR3 when sink doesn't support
> >> TPS4") introduced a blanket rejection of HBR3 link rate when the sink does
> >> not support TPS4. While this was intended to address instability observed
> >> on certain eDP panels [1], the TPS4 requirement is only mandated for DPRX
> >> and not for eDPRX.
> > I see no exception given for eDP regarding this rule. The only exception
> > allowed is that eDP can say DPCD_REV=1.4 + TPS4_SUPPORTED=0. So I still
> > claim that these eDP sinks are violating the spec.
> 
> Hmm.. Yes the spec allows eDP sinks to report DPCD_REV=1.4 and 
> TPS4_SUPPORTED, so perhaps eDPs claiming HBR3 with DPCD rev other than 
> rev 1.4 and not supporting TPS4 are indeed violating the spec.
> 
> Would it make sense to add a condition that checks for DPCD_REV=1.4.
> 
> Specifically:
> 
> if DPCD_REV=1.4 and TPS4_SUPPORTED = 0, then do not prune the HBR3 rate?
> 
> Or otherway if DPCD_REV!=1.4 and TPS4_SUPPORTER = 0, prune the HBR3 rate
> 
> This way the patch need not be reverted, but modified to address 
> instability issues for eDP panels that are not aligned with the spec.
> 
> That said, the gitlab issue#5969 [1] will still need another solution 
> since it seems to have DPCD rev 14 as per logs:
> 
> DPCD: 14 1e 44 41 00 00 01 80 02 00 02 00 00 0b 80

I think we do need the quirk. But the commit message should IMO be
adjusted so that it doesn't claim that these panels are 100% legal.

-- 
Ville Syrjälä
Intel