On Sun, Sep 21, 2025 at 10:05:29AM +0530, Ankit Nautiyal wrote:
> For TGL the TRANS_SET_CONTEXT_LATENCY doesn't exist to account for SCL.
> However, the VBLANK_START-VACTIVE diffence plays an identical role here ie.
> it can be used to create the SCL window ahead of the undelayed vblank.
>
> While readback there is no specific register to read out the SCL, so use
> the same helper intel_crtc_compute_scl() and reduce the vblank_start by
> this amount.
>
> Signed-off-by: Ankit Nautiyal <[email protected]>
> ---
> drivers/gpu/drm/i915/display/intel_display.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c
> b/drivers/gpu/drm/i915/display/intel_display.c
> index 5a7794387ea2..455bbebb50a5 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -2822,6 +2822,16 @@ static void intel_get_transcoder_timings(struct
> intel_crtc *crtc,
> adjusted_mode->crtc_vblank_end += 1;
> }
>
> + if (DISPLAY_VER(display) == 12) {
> + /*
> + * There is no specific register for SCL for TGL.
> + * Derive the value from the helper
> intel_crtc_set_context_latency().
> + * crtc_vblank_start needs to be reduced with this amount.
> + */
> + pipe_config->set_context_latency =
> intel_crtc_set_context_latency(pipe_config);
That thing *computes* the SCL, it doesn't teel us what the
current hw value is.
> + adjusted_mode->crtc_vblank_start -=
> pipe_config->set_context_latency;
> + }
> +
> if (DISPLAY_VER(display) >= 13 && !transcoder_is_dsi(cpu_transcoder)) {
> pipe_config->set_context_latency =
> intel_de_read(display,
I think this whole thing needs to look something like this:
if (DISPLAY_VER >= 13 && !dsi) {
set_context_latency = read(TRANS_SET_CONTEXT_LATENCY);
crtc_vblank_start = crtc_vdisplay + set_set_context_latency;
} else if (DISPLAY_VER >= 12) {
set_context_latency = crtc_vblank_start - crtc_vdisplay;
}
That'll also cover DSI (not that the DSI code itself is actually
ready for SCL...).
And I think you need to squash this into the set_context_latency
patch. Otherwise we'll get state checker mismatches on TGL in
between.
--
Ville Syrjälä
Intel
