Re: [PATCH v3 20/26] drm/i915/writeback: Configure WD_STRIDE reg

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

On Wed, Mar 25, 2026 at 04:37:38PM +0530, Suraj Kandpal wrote:
> Write to the WD_STRIDE register using the appropriate calculation
> based on the color mode and hactive.
> 
> Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
> ---
>  .../gpu/drm/i915/display/intel_writeback.c    | 36 +++++++++++++++++++
>  .../drm/i915/display/intel_writeback_reg.h    |  1 +
>  2 files changed, 37 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_writeback.c b/drivers/gpu/drm/i915/display/intel_writeback.c
> index d3c3716a28a9..e2f7c46015d2 100644
> --- a/drivers/gpu/drm/i915/display/intel_writeback.c
> +++ b/drivers/gpu/drm/i915/display/intel_writeback.c
> @@ -231,15 +231,51 @@ static int intel_writeback_atomic_check(struct drm_connector *connector,
>  	return 0;
>  }
>  
> +static int
> +get_color_mode_bpp(struct intel_display *display, u32 color_format)
> +{
> +	int bpp = 0;
> +
> +	switch (color_format) {
> +	case DRM_FORMAT_XYUV8888:
> +	case DRM_FORMAT_YUYV:
> +	case DRM_FORMAT_VYUY:
> +	case DRM_FORMAT_XBGR8888:
> +	case DRM_FORMAT_XBGR2101010:
> +	case DRM_FORMAT_XVYU2101010:
> +		bpp = 4;
> +		break;
> +	default:
> +		drm_err(display->drm, "Unsupported format for writeback\n");
> +		break;
> +	}
> +
> +	return bpp;
> +}
> +
>  static void intel_writeback_capture(struct intel_atomic_state *state,
>  				    struct intel_connector *connector)
>  {
>  	struct intel_display *display = to_intel_display(connector);
>  	struct intel_writeback_connector *wb_conn =
>  		conn_to_intel_writeback_connector(connector);
> +	struct drm_connector_state *conn_state =
> +		drm_atomic_get_new_connector_state(&state->base, &connector->base);
> +	struct intel_crtc *crtc = intel_crtc_for_pipe(display, wb_conn->pipe);
> +	struct intel_crtc_state *crtc_state =
> +		intel_atomic_get_new_crtc_state(state, crtc);
> +	const struct drm_display_mode *adjusted_mode =
> +		&crtc_state->hw.adjusted_mode;
> +	struct drm_writeback_job *wb_job = conn_state->writeback_job;
>  	enum transcoder trans = wb_conn->trans;
>  	u32 val = 0;
> +	int bpp;
>  
> +	bpp = get_color_mode_bpp(display, wb_job->fb->format->format);
> +	val = DIV_ROUND_UP((adjusted_mode->hdisplay * bpp), 64);

The fb should tell us its stride.

> +	intel_de_write(display, WD_STRIDE(trans), WD_STRIDE_VAL(val));
> +
> +	val = 0;
>  	val |= START_TRIGGER_FRAME | WD_FRAME_NUMBER(wb_conn->frame_num);
>  	intel_de_rmw(display, WD_TRANS_FUNC_CTL(trans),
>  		     START_TRIGGER_FRAME | WD_FRAME_NUMBER_MASK,
> diff --git a/drivers/gpu/drm/i915/display/intel_writeback_reg.h b/drivers/gpu/drm/i915/display/intel_writeback_reg.h
> index 5e7c6c99d191..f526af0f9aff 100644
> --- a/drivers/gpu/drm/i915/display/intel_writeback_reg.h
> +++ b/drivers/gpu/drm/i915/display/intel_writeback_reg.h
> @@ -60,6 +60,7 @@
>  					_WD_STRIDE_0,\
>  					_WD_STRIDE_1)
>  #define WD_STRIDE_MASK			REG_GENMASK(15, 6)
> +#define WD_STRIDE_VAL(val)		REG_FIELD_PREP(WD_STRIDE_MASK, val)
>  
>  #define _WD_STREAMCAP_CTL0		0x6e590
>  #define _WD_STREAMCAP_CTL1		0x6ed90
> -- 
> 2.34.1

-- 
Ville Syrjälä
Intel