Re: [Intel-gfx] [PATCH 2/2] drm/i915/dp: For PCON TMDS mode set only the relavant bits in config DPCD

["Shankar, Uma" <uma.shankar@intel.com>]

> -----Original Message-----
> From: Nautiyal, Ankit K <ankit.k.nautiyal@intel.com>
> Sent: Friday, October 29, 2021 11:32 AM
> To: intel-gfx@lists.freedesktop.org
> Cc: Sharma, Swati2 <swati2.sharma@intel.com>; Shankar, Uma
> <uma.shankar@intel.com>
> Subject: [PATCH 2/2] drm/i915/dp: For PCON TMDS mode set only the relavant bits
> in config DPCD
> 
> Currently we reset the whole PCON linkConfig DPCD to set the TMDS mode.
> This also resets the Source control bit and HDMI link enable bit and goes to
> autonomous mode of operation, which is seen to spoil the PCONs internal state.
> 
> This patch avoids resetting the PCON link config register and sets only TMDS mode
> bit, Source control bit in the configuration DPCD.
> It then enables the HDMI Link Enable bit.
> 
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> b/drivers/gpu/drm/i915/display/intel_dp.c
> index f5fd106e555c..3df35079580a 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -2287,6 +2287,29 @@ static bool intel_dp_is_hdmi_2_1_sink(struct intel_dp
> *intel_dp)
>  	return false;
>  }
> 
> +static
> +int intel_dp_pcon_set_tmds_mode(struct intel_dp *intel_dp) {
> +	int ret;
> +	u8 buf = 0;
> +
> +	/* Set PCON source control mode and TMDS */
> +	buf |= DP_PCON_ENABLE_SOURCE_CTL_MODE;
> +	buf &= ~DP_PCON_ENABLE_MAX_FRL_BW;
> +

I don't see setting this to TMDS, we should be still in FRL mode as bit5 is not being reset here.
Am I missing something ?

Regards,
Uma Shankar
> +	ret = drm_dp_dpcd_writeb(&intel_dp->aux,
> DP_PCON_HDMI_LINK_CONFIG_1, buf);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set HDMI LINK ENABLE */
> +	buf |= DP_PCON_ENABLE_HDMI_LINK;
> +	ret = drm_dp_dpcd_writeb(&intel_dp->aux,
> DP_PCON_HDMI_LINK_CONFIG_1, buf);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +
>  void intel_dp_check_frl_training(struct intel_dp *intel_dp)  {
>  	struct drm_i915_private *dev_priv = dp_to_i915(intel_dp); @@ -2305,7
> +2328,7 @@ void intel_dp_check_frl_training(struct intel_dp *intel_dp)
>  		int ret, mode;
> 
>  		drm_dbg(&dev_priv->drm, "Couldn't set FRL mode, continuing with
> TMDS mode\n");
> -		ret = drm_dp_pcon_reset_frl_config(&intel_dp->aux);
> +		ret = intel_dp_pcon_set_tmds_mode(intel_dp);
>  		mode = drm_dp_pcon_hdmi_link_mode(&intel_dp->aux, NULL);
> 
>  		if (ret < 0 || mode != DP_PCON_HDMI_MODE_TMDS)
> --
> 2.25.1