[Intel-gfx] [PATCH v3] drm/i915/hdmi: Go for scrambling only if platform supports TMDS clock > 340MHz

[Shankar, Uma]

> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of Ankit
> Nautiyal
> Sent: Thursday, December 22, 2022 9:39 AM
> To: intel-gfx at lists.freedesktop.org
> Subject: [Intel-gfx] [PATCH v3] drm/i915/hdmi: Go for scrambling only if platform
> supports TMDS clock > 340MHz
> 
> There are cases, where devices have an HDMI1.4 retimer, and TMDS clock rate is
> capped to 340MHz via VBT. In such cases scrambling might be supported by the
> platform and an HDMI2.0 sink for lower TMDS rates, but not supported by the
> retimer, causing blankouts.
> 
> So avoid enabling scrambling, if the TMDS clock is capped to <= 340MHz.
> 
> v2: Added comment, documenting the rationale to check for TMDS clock, before
> going for scrambling. (Arun)
> 
> v3: Fixed the function name to check if source supports scrambling. (Jani)

Pushed to drm-intel-next. Thanks for the patch and reviews.

Regards,
Uma Shankar

> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
> Reviewed-by: Arun R Murthy <arun.r.murthy at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_hdmi.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c
> b/drivers/gpu/drm/i915/display/intel_hdmi.c
> index efa2da080f62..dd3465f992f8 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdmi.c
> +++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
> @@ -2244,6 +2244,25 @@ static bool intel_hdmi_is_cloned(const struct
> intel_crtc_state *crtc_state)
>  		!is_power_of_2(crtc_state->uapi.encoder_mask);
>  }
> 
> +static bool source_supports_scrambling(struct intel_encoder *encoder) {
> +	/*
> +	 * Gen 10+ support HDMI 2.0 : the max tmds clock is 594MHz, and
> +	 * scrambling is supported.
> +	 * But there seem to be cases where certain platforms that support
> +	 * HDMI 2.0, have an HDMI1.4 retimer chip, and the max tmds clock is
> +	 * capped by VBT to less than 340MHz.
> +	 *
> +	 * In such cases when an HDMI2.0 sink is connected, it creates a
> +	 * problem : the platform and the sink both support scrambling but the
> +	 * HDMI 1.4 retimer chip doesn't.
> +	 *
> +	 * So go for scrambling, based on the max tmds clock taking into account,
> +	 * restrictions coming from VBT.
> +	 */
> +	return intel_hdmi_source_max_tmds_clock(encoder) > 340000; }
> +
>  int intel_hdmi_compute_config(struct intel_encoder *encoder,
>  			      struct intel_crtc_state *pipe_config,
>  			      struct drm_connector_state *conn_state) @@ -2301,7
> +2320,7 @@ int intel_hdmi_compute_config(struct intel_encoder *encoder,
> 
>  	pipe_config->lane_count = 4;
> 
> -	if (scdc->scrambling.supported && DISPLAY_VER(dev_priv) >= 10) {
> +	if (scdc->scrambling.supported && source_supports_scrambling(encoder))
> +{
>  		if (scdc->scrambling.low_rates)
>  			pipe_config->hdmi_scrambling = true;
> 
> --
> 2.25.1