Re: [Intel-gfx] [PATCH 4/4] drm/i915: Extract intel_crtc_scanline_offset()

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 06 Mar 2023, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Pull the scanline_offset calculation into its own function. Might
> have further use for this later with DSB scanline waits.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_vblank.c | 89 +++++++++++----------
>  1 file changed, 48 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_vblank.c b/drivers/gpu/drm/i915/display/intel_vblank.c
> index 48bf3923af11..f8bf9810527d 100644
> --- a/drivers/gpu/drm/i915/display/intel_vblank.c
> +++ b/drivers/gpu/drm/i915/display/intel_vblank.c
> @@ -441,6 +441,53 @@ void intel_wait_for_pipe_scanline_moving(struct intel_crtc *crtc)
>  	wait_for_pipe_scanline_moving(crtc, true);
>  }
>  
> +static int intel_crtc_scanline_offset(const struct intel_crtc_state *crtc_state)
> +{
> +	struct drm_i915_private *i915 = to_i915(crtc_state->uapi.crtc->dev);
> +	const struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
> +
> +	/*
> +	 * The scanline counter increments at the leading edge of hsync.
> +	 *
> +	 * On most platforms it starts counting from vtotal-1 on the
> +	 * first active line. That means the scanline counter value is
> +	 * always one less than what we would expect. Ie. just after
> +	 * start of vblank, which also occurs at start of hsync (on the
> +	 * last active line), the scanline counter will read vblank_start-1.
> +	 *
> +	 * On gen2 the scanline counter starts counting from 1 instead
> +	 * of vtotal-1, so we have to subtract one (or rather add vtotal-1
> +	 * to keep the value positive), instead of adding one.
> +	 *
> +	 * On HSW+ the behaviour of the scanline counter depends on the output
> +	 * type. For DP ports it behaves like most other platforms, but on HDMI
> +	 * there's an extra 1 line difference. So we need to add two instead of
> +	 * one to the value.
> +	 *
> +	 * On VLV/CHV DSI the scanline counter would appear to increment
> +	 * approx. 1/3 of a scanline before start of vblank. Unfortunately
> +	 * that means we can't tell whether we're in vblank or not while
> +	 * we're on that particular line. We must still set scanline_offset
> +	 * to 1 so that the vblank timestamps come out correct when we query
> +	 * the scanline counter from within the vblank interrupt handler.
> +	 * However if queried just before the start of vblank we'll get an
> +	 * answer that's slightly in the future.
> +	 */
> +	if (DISPLAY_VER(i915) == 2) {
> +		int vtotal;
> +
> +		vtotal = adjusted_mode->crtc_vtotal;
> +		if (adjusted_mode->flags & DRM_MODE_FLAG_INTERLACE)
> +			vtotal /= 2;
> +
> +		return vtotal - 1;
> +	} else if (HAS_DDI(i915) && intel_crtc_has_type(crtc_state, INTEL_OUTPUT_HDMI)) {
> +		return 2;
> +	} else {
> +		return 1;
> +	}
> +}
> +
>  void intel_crtc_update_active_timings(const struct intel_crtc_state *crtc_state)
>  {
>  	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> @@ -479,47 +526,7 @@ void intel_crtc_update_active_timings(const struct intel_crtc_state *crtc_state)
>  
>  	crtc->mode_flags = crtc_state->mode_flags;
>  
> -	/*
> -	 * The scanline counter increments at the leading edge of hsync.
> -	 *
> -	 * On most platforms it starts counting from vtotal-1 on the
> -	 * first active line. That means the scanline counter value is
> -	 * always one less than what we would expect. Ie. just after
> -	 * start of vblank, which also occurs at start of hsync (on the
> -	 * last active line), the scanline counter will read vblank_start-1.
> -	 *
> -	 * On gen2 the scanline counter starts counting from 1 instead
> -	 * of vtotal-1, so we have to subtract one (or rather add vtotal-1
> -	 * to keep the value positive), instead of adding one.
> -	 *
> -	 * On HSW+ the behaviour of the scanline counter depends on the output
> -	 * type. For DP ports it behaves like most other platforms, but on HDMI
> -	 * there's an extra 1 line difference. So we need to add two instead of
> -	 * one to the value.
> -	 *
> -	 * On VLV/CHV DSI the scanline counter would appear to increment
> -	 * approx. 1/3 of a scanline before start of vblank. Unfortunately
> -	 * that means we can't tell whether we're in vblank or not while
> -	 * we're on that particular line. We must still set scanline_offset
> -	 * to 1 so that the vblank timestamps come out correct when we query
> -	 * the scanline counter from within the vblank interrupt handler.
> -	 * However if queried just before the start of vblank we'll get an
> -	 * answer that's slightly in the future.
> -	 */
> -	if (DISPLAY_VER(i915) == 2) {
> -		int vtotal;
> -
> -		vtotal = adjusted_mode.crtc_vtotal;
> -		if (adjusted_mode.flags & DRM_MODE_FLAG_INTERLACE)
> -			vtotal /= 2;
> -
> -		crtc->scanline_offset = vtotal - 1;
> -	} else if (HAS_DDI(i915) &&
> -		   intel_crtc_has_type(crtc_state, INTEL_OUTPUT_HDMI)) {
> -		crtc->scanline_offset = 2;
> -	} else {
> -		crtc->scanline_offset = 1;
> -	}
> +	crtc->scanline_offset = intel_crtc_scanline_offset(crtc_state);
>  
>  	spin_unlock(&i915->uncore.lock);
>  	spin_unlock_irqrestore(&i915->drm.vblank_time_lock, irqflags);

-- 
Jani Nikula, Intel Open Source Graphics Center