[Intel-gfx] [PATCH] drm/i915/tgl/psr: Fix glitches when doing frontbuffer modifications

[Mun, Gwan-gyeong]

After applying this patch, the psr screen glitch issue is still seen.
On Fri, 2020-10-02 at 16:16 -0700, José Roberto de Souza wrote:
> Writes to CURSURFLIVE in TGL are causing IOMMU errors and visual
> glitches that are often reproduced when executing CPU intensive
> workloads while a eDP 4K panel is attached.
> 
> Manually exiting PSR causes the frontbuffer to be updated without
> glitches and the IOMMU errors are also gone but this comes at the
> cost
> of less time with PSR active.
> 
> So using this workaround until this issue is root caused and a better
> fix is found.
> 
> The current code is already ready to enable PSR after this exit if
> there is not other frontbuffer modifications.
> 
> Adding a new if block in psr_force_hw_tracking_exit() instead of
> reuse
> the else/gen8- block because the plan is to revert this workaround
> as soon as a better solution is found.
> 
> Cc: Gwan-gyeong Mun <gwan-gyeong.mun at intel.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_psr.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_psr.c
> b/drivers/gpu/drm/i915/display/intel_psr.c
> index 8a9d0bdde1bf..8630121dbbbe 100644
> --- a/drivers/gpu/drm/i915/display/intel_psr.c
> +++ b/drivers/gpu/drm/i915/display/intel_psr.c
> @@ -1152,7 +1152,21 @@ void intel_psr_disable(struct intel_dp
> *intel_dp,
>  
>  static void psr_force_hw_tracking_exit(struct drm_i915_private
> *dev_priv)
>  {
> -	if (INTEL_GEN(dev_priv) >= 9)
> +	if (IS_TIGERLAKE(dev_priv))
> +		/*
> +		 * Writes to CURSURFLIVE in TGL are causing IOMMU
> errors and
> +		 * visual glitches that are often reproduced when
> executing
> +		 * CPU intensive workloads while a eDP 4K panel is
> attached.
> +		 *
> +		 * Manually exiting PSR causes the frontbuffer to be
> updated
> +		 * without glitches and the IOMMU errors are also gone
> but
> +		 * this comes at the cost of less time with PSR active.
> +		 *
> +		 * So using this workaround until this issue is root
> caused
> +		 * and a better fix is found.
> +		 */
> +		intel_psr_exit(dev_priv);
> +	else if (INTEL_GEN(dev_priv) >= 9)
>  		/*
>  		 * Display WA #0884: skl+
>  		 * This documented WA for bxt can be safely applied