Re: [PATCH 4/7] drm/i915: Simplify scanline_offset handling for gen2

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

On Tue, 28 May 2024, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Currently intel_crtc_scanline_offset() is careful to always
> return a positive offset. That is not actually necessary
> as long as we take care of negative values when applying the
> offset in __intel_get_crtc_scanline().
>
> This simplifies intel_crtc_scanline_offset(), and makes
> the scanline_offfset arithmetic more symmetric between
> the forwad (__intel_get_crtc_scanline()) and reverse

*forward

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

> (intel_crtc_scanline_to_hw()) directions.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_vblank.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_vblank.c b/drivers/gpu/drm/i915/display/intel_vblank.c
> index 31fa5867e1a7..b0e95a4c680d 100644
> --- a/drivers/gpu/drm/i915/display/intel_vblank.c
> +++ b/drivers/gpu/drm/i915/display/intel_vblank.c
> @@ -240,7 +240,7 @@ static int __intel_get_crtc_scanline(struct intel_crtc *crtc)
>  	 * See update_scanline_offset() for the details on the
>  	 * scanline_offset adjustment.
>  	 */
> -	return (position + crtc->scanline_offset) % vtotal;
> +	return (position + vtotal + crtc->scanline_offset) % vtotal;
>  }
>  
>  int intel_crtc_scanline_to_hw(struct intel_crtc *crtc, int scanline)
> @@ -470,7 +470,6 @@ void intel_wait_for_pipe_scanline_moving(struct intel_crtc *crtc)
>  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.
> @@ -482,8 +481,7 @@ static int intel_crtc_scanline_offset(const struct intel_crtc_state *crtc_state)
>  	 * 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.
> +	 * of vtotal-1, so we have to subtract 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
> @@ -500,7 +498,7 @@ static int intel_crtc_scanline_offset(const struct intel_crtc_state *crtc_state)
>  	 * answer that's slightly in the future.
>  	 */
>  	if (DISPLAY_VER(i915) == 2)
> -		return intel_mode_vtotal(adjusted_mode) - 1;
> +		return -1;
>  	else if (HAS_DDI(i915) && intel_crtc_has_type(crtc_state, INTEL_OUTPUT_HDMI))
>  		return 2;
>  	else

-- 
Jani Nikula, Intel