ACK/Cmnt: [H/I/Unstable/OEM-5.13/OEM-5.14] [PATCH 2/2] drm/i915/dp: Use max params for panels < eDP 1.4

[Stefan Bader]

On 08.09.21 04:42, Kai-Heng Feng wrote:
> BugLink: https://bugs.launchpad.net/bugs/1942972
> 
> Users reported that after commit 2bbd6dba84d4 ("drm/i915: Try to use
> fast+narrow link on eDP again and fall back to the old max strategy on
> failure"), the screen starts to have wobbly effect.
> 
> Commit a5c936add6a2 ("drm/i915/dp: Use slow and wide link training for
> everything") doesn't help either, that means the affected eDP 1.2 panels
> only work with max params.
> 
> So use max params for panels < eDP 1.4 as Windows does to solve the
> issue.
> 
> v3:
>   - Do the eDP rev check in intel_edp_init_dpcd()
> 
> v2:
>   - Check eDP 1.4 instead of DPCD 1.1 to apply max params
> 
> Cc: stable at vger.kernel.org
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/3714
> Fixes: 2bbd6dba84d4 ("drm/i915: Try to use fast+narrow link on eDP again and fall back to the old max strategy on failure")
> Fixes: a5c936add6a2 ("drm/i915/dp: Use slow and wide link training for everything")
> Suggested-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Link: https://patchwork.freedesktop.org/patch/msgid/20210820075301.693099-1-kai.heng.feng@canonical.com
- (cherry picked from commit d7f213c131adf0bec8b731553eb82990cdac265d 
git://anongit.freedesktop.org/drm/drm-tip drm-tip)
+ (cherry picked from commit d7f213c131adf0bec8b731553eb82990cdac265d)
+ Signed-off-by: Jani Nikula <jani.nikula at intel.com>
+ (cherry picked from commit c8dead5751b81dfa6b10449b740ed1062ff670c5)
> Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---

This is now upstream (v5.15-rc2). S-O-B to be updated when applying.

-Stefan

>   drivers/gpu/drm/i915/display/intel_dp.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 862c1df69cc2a..d511e578ba79d 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -2453,11 +2453,14 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
>   	 */
>   	if (drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_DPCD_REV,
>   			     intel_dp->edp_dpcd, sizeof(intel_dp->edp_dpcd)) ==
> -			     sizeof(intel_dp->edp_dpcd))
> +			     sizeof(intel_dp->edp_dpcd)) {
>   		drm_dbg_kms(&dev_priv->drm, "eDP DPCD: %*ph\n",
>   			    (int)sizeof(intel_dp->edp_dpcd),
>   			    intel_dp->edp_dpcd);
>   
> +		intel_dp->use_max_params = intel_dp->edp_dpcd[0] < DP_EDP_14;
> +	}
> +
>   	/*
>   	 * This has to be called after intel_dp->edp_dpcd is filled, PSR checks
>   	 * for SET_POWER_CAPABLE bit in intel_dp->edp_dpcd[1]
> 


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