[PATCH 4/4] drm/i915/display: Set TRANS_DDI_MODE_SELECT to default value when disabling TRANS_DDI

[Lisovskiy, Stanislav]

On Thu, 2020-01-16 at 17:58 -0800, José Roberto de Souza wrote:
> TGL timeouts when disabling MST transcoder and fifo underruns over
> MST
> transcoders are fixed when setting TRANS_DDI_MODE_SELECT to 0(HDMI
> mode) during the disable sequence.
> 
> Although BSpec disable sequence don't require this step it is a
> harmless change and it is also done by Windows driver.
> Anyhow HW team was notified about that but it can take some time to
> documentation to be updated.
> 
> A case that always lead to those issues is:
> - do a modeset enabling pipe A and pipe B in the same MST stream
> leaving A as master
> - disable pipe A, promote B as master doing a full modeset in A
> - enable pipe A, changing the master transcoder back to A(doing a
> full modeset in B)
> - Pow: underruns and timeouts
> 
> The transcoders involved will only work again when complete disabled
> and their power wells turned off causing a reset in their registers.
> 
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Matt Roper <matthew.d.roper at intel.com>
> Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_ddi.c | 1 +
>  1 file changed, 1 insertion(+)

BAT/IGT are fine, so if this improves some MST behaviors don't see
any point in holding this patch from being merged. 
For MST, we are anyway facing MST regressions almost on weekly basis.
Until we have some meaningful tests in CI for MST, it anyway
would be constantly in "bad" shape.

Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>

> 
> diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c
> b/drivers/gpu/drm/i915/display/intel_ddi.c
> index 32ea3c7e8b62..82e90f271974 100644
> --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> @@ -1997,6 +1997,7 @@ void intel_ddi_disable_transcoder_func(const
> struct intel_crtc_state *crtc_state
>  
>  	val = I915_READ(TRANS_DDI_FUNC_CTL(cpu_transcoder));
>  	val &= ~TRANS_DDI_FUNC_ENABLE;
> +	val &= ~TRANS_DDI_MODE_SELECT_MASK;
>  
>  	if (INTEL_GEN(dev_priv) >= 12) {
>  		if (!intel_dp_mst_is_master_trans(crtc_state))