Re: [PATCH 09/11] drm/i915: Program DB LUT registers before vblank

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

On Mon, Apr 07, 2025 at 07:53:57PM +0530, Chaitanya Kumar Borah wrote:
> Double Buffered LUT registers can be programmed in the active region.
> This patch implements the MMIO path for it. Program the registers after
> evading vblank. The HW latches on to the registers after delayed vblank.
> It takes around 1024 cdclk cycles(~one scanline) for this.
> 
> Following assumptions have been made while making this change
> 
>  - Current vblank evasion time is sufficient for programming
>    the LUT registers.
>  - Current guardband calculation would be sufficient for the HW
>    to latch on to the new values
> 
> Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 85e28b4c9e66..df9c992d2939 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -6725,10 +6725,12 @@ static void intel_pre_update_crtc(struct intel_atomic_state *state,
>  static void intel_update_crtc(struct intel_atomic_state *state,
>  			      struct intel_crtc *crtc)
>  {
> +	struct intel_display *display = to_intel_display(crtc);
>  	const struct intel_crtc_state *old_crtc_state =
>  		intel_atomic_get_old_crtc_state(state, crtc);
>  	struct intel_crtc_state *new_crtc_state =
>  		intel_atomic_get_new_crtc_state(state, crtc);
> +	bool modeset = intel_crtc_needs_modeset(new_crtc_state);
>  
>  	if (new_crtc_state->use_dsb) {
>  		intel_crtc_prepare_vblank_event(new_crtc_state, &crtc->dsb_event);
> @@ -6738,6 +6740,12 @@ static void intel_update_crtc(struct intel_atomic_state *state,
>  		/* Perform vblank evasion around commit operation */
>  		intel_pipe_update_start(state, crtc);
>  
> +		if (!modeset &&
> +		    intel_crtc_needs_color_update(new_crtc_state) &&
> +		    !new_crtc_state->dsb_color &&
> +		    HAS_DOUBLE_BUFFERED_LUT(display))
> +			intel_color_load_luts(new_crtc_state);
> +

I think we want to do this in commit_pipe_post_planes() since
a vblank evasion failure for this is probably less drastic than
for plane programming.

>  		if (new_crtc_state->dsb_commit)
>  			intel_dsb_commit(new_crtc_state->dsb_commit, false);
>  
> -- 
> 2.25.1

-- 
Ville Syrjälä
Intel