Re: [PATCH 02/12] drm/i915/vrr: Add helper to readback EMP_AS_SDP_TL

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

On Mon, Apr 13, 2026 at 09:23:39AM +0530, Ankit Nautiyal wrote:
> EMP_AS_SDP_TL is used to program both DP Adaptive Sync SDP and HDMI
> Video Timing EMP for VRR operation. Add a helper to read back the
> programmed transmission line from hardware so VRR code can populate
> the corresponding CRTC state fields during get_config.
> 
> This provides a common read-back path for VRR packet transmission
> line state.
> 
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_vrr.c | 13 +++++++++++++
>  drivers/gpu/drm/i915/display/intel_vrr.h |  1 +
>  2 files changed, 14 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
> index 1fed597439b0..abdae7f1f8a8 100644
> --- a/drivers/gpu/drm/i915/display/intel_vrr.c
> +++ b/drivers/gpu/drm/i915/display/intel_vrr.c
> @@ -1218,3 +1218,16 @@ int intel_vrr_dcb_vmax_vblank_start_final(const struct intel_crtc_state *crtc_st
>  
>  	return intel_vrr_vblank_start(crtc_state, VRR_DCB_VMAX(tmp) + 1);
>  }
> +
> +u16 intel_vrr_read_emp_as_sdp_tl(const struct intel_crtc_state *crtc_state)
> +{
> +	struct intel_display *display = to_intel_display(crtc_state);
> +	enum transcoder cpu_transcoder = crtc_state->cpu_transcoder;
> +	u32 val;
> +
> +	if (!HAS_EMP_AS_SDP_TL(display))
> +		return 0;
> +
> +	val = intel_de_read(display, EMP_AS_SDP_TL(display, cpu_transcoder));
> +	return REG_FIELD_GET(EMP_AS_SDP_DB_TL_MASK, val);

This stuff really doesn't seem to belong in intel_vrr.c. We probably need
some kind of infoframe/SDP file where all the relevant stuff lives. Long
ago I did attempt to extract all the infoframe stuff from intel_hdmi.c
into intel_dip.c (or something like that), but there were still far too
many HDMI specifics in the result for my liking.

So I think what's really needed is an effort to distill the core of the
video DIP implementation (really just the low level buffer read/write
stuff, and I suspect now also this transmission line stuff) into a new
file. You could perhaps introduce that new file here, and then we'll
try to get to extracting the DIP buffer stuff later.

> +}
> diff --git a/drivers/gpu/drm/i915/display/intel_vrr.h b/drivers/gpu/drm/i915/display/intel_vrr.h
> index 4f16ca4af91f..6659a8a53432 100644
> --- a/drivers/gpu/drm/i915/display/intel_vrr.h
> +++ b/drivers/gpu/drm/i915/display/intel_vrr.h
> @@ -53,5 +53,6 @@ int intel_vrr_dcb_vmin_vblank_start_next(const struct intel_crtc_state *crtc_sta
>  int intel_vrr_dcb_vmax_vblank_start_next(const struct intel_crtc_state *crtc_state);
>  int intel_vrr_dcb_vmin_vblank_start_final(const struct intel_crtc_state *crtc_state);
>  int intel_vrr_dcb_vmax_vblank_start_final(const struct intel_crtc_state *crtc_state);
> +u16 intel_vrr_read_emp_as_sdp_tl(const struct intel_crtc_state *crtc_state);
>  
>  #endif /* __INTEL_VRR_H__ */
> -- 
> 2.45.2

-- 
Ville Syrjälä
Intel