[Intel-gfx] [PATCH v2 14/19] drm/i915/dsb: Evade transcoder undelayed vblank when using DSB

[Shankar, Uma]

> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of Ville
> Syrjala
> Sent: Wednesday, June 7, 2023 12:45 AM
> To: intel-gfx at lists.freedesktop.org
> Subject: [Intel-gfx] [PATCH v2 14/19] drm/i915/dsb: Evade transcoder undelayed
> vblank when using DSB
> 
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> We want to start the DSB execution from the transcoder's undelayed vblank, so in
> order to guarantee atomicity with the all the other mmio register writes we need
> to evade both vblanks.
> 
> Note that currently we don't add any vblank delay, so this is effectively a nop. But
> in the future when we start to program double buffered registers from the DSB
> we'll need to delay the pipe's vblank to provide the register programming
> "window2"
> for the DSB.

Agree with this, looks good.
Reviewed-by: Uma Shankar <uma.shankar at intel.com>

> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_crtc.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_crtc.c
> b/drivers/gpu/drm/i915/display/intel_crtc.c
> index 36c9b590a058..ff0ebdf7cde3 100644
> --- a/drivers/gpu/drm/i915/display/intel_crtc.c
> +++ b/drivers/gpu/drm/i915/display/intel_crtc.c
> @@ -519,8 +519,12 @@ void intel_pipe_update_start(struct intel_crtc_state
> *new_crtc_state)
>  	/*
>  	 * M/N is double buffered on the transcoder's undelayed vblank,
>  	 * so with seamless M/N we must evade both vblanks.
> +	 *
> +	 * DSB execution waits for the transcoder's undelayed vblank,
> +	 * hence we must kick off the commit before that.
>  	 */
> -	if (new_crtc_state->seamless_m_n &&
> intel_crtc_needs_fastset(new_crtc_state))
> +	if (new_crtc_state->dsb ||
> +	    (new_crtc_state->seamless_m_n &&
> +intel_crtc_needs_fastset(new_crtc_state)))
>  		min -= adjusted_mode->crtc_vblank_start - adjusted_mode-
> >crtc_vdisplay;
> 
>  	if (min <= 0 || max <= 0)
> --
> 2.39.3