[PATCH] drm/i915/dp: Add FEC Enable Retry mechanism

[Srikanth V, NagaVenkata]

> -----Original Message-----
> From: Intel-xe <intel-xe-bounces at lists.freedesktop.org> On Behalf Of
> Chaitanya Kumar Borah
> Sent: Monday, September 23, 2024 10:22 AM
> To: intel-gfx at lists.freedesktop.org; intel-xe at lists.freedesktop.org
> Subject: [PATCH] drm/i915/dp: Add FEC Enable Retry mechanism
> 
> From PTL, FEC_DECODE_EN sequence can be sent to a DPRX independent of
> TRANS_CONF enable. This allows us to re-issue an FEC_DECODE_EN sequence
> without re-doing the whole mode set sequence. This separate control over
> FEC_ECODE_EN/DIS sequence enables us to have a retry mechanism in case the
> DPRX does not respond with an FEC_ENABLE within the stipulated 5ms.
> 
> Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_ddi.c | 61 +++++++++++++++++++++++-
>  1 file changed, 59 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c
> b/drivers/gpu/drm/i915/display/intel_ddi.c
> index 85e519a21542..589acea9906a 100644
> --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> @@ -78,6 +78,8 @@
>  #include "skl_scaler.h"
>  #include "skl_universal_plane.h"
> 
> +#define FEC_RETRY_COUNT 3
> +
>  static const u8 index_to_dp_signal_levels[] = {
>  	[0] = DP_TRAIN_VOLTAGE_SWING_LEVEL_0 |
> DP_TRAIN_PRE_EMPH_LEVEL_0,
>  	[1] = DP_TRAIN_VOLTAGE_SWING_LEVEL_0 |
> DP_TRAIN_PRE_EMPH_LEVEL_1, @@ -2255,6 +2257,57 @@ static int
> read_fec_detected_status(struct drm_dp_aux *aux)
>  	return status;
>  }
> 
> +static void retry_fec_enable(struct intel_encoder *encoder,
> +			     const struct intel_crtc_state *crtc_state,
> +			     struct drm_dp_aux *aux)
> +{
> +	struct drm_i915_private *i915 = to_i915(aux->drm_dev);
> +	int ret = 0;
> +

You should also be clearing FEC_ENABLE_LIVE_STATUS in DP_TP_STATUS register by writing 1.

> +	/* Clear FEC enable */
> +	intel_de_rmw(i915, dp_tp_ctl_reg(encoder, crtc_state),
> +		     DP_TP_CTL_FEC_ENABLE, 0);
> +

> +	/* Set FEC enable */
> +	intel_de_rmw(i915, dp_tp_ctl_reg(encoder, crtc_state),
> +		     0, DP_TP_CTL_FEC_ENABLE);
> +
> +	ret = intel_de_wait_for_set(i915, dp_tp_status_reg(encoder,
> crtc_state),
> +				    DP_TP_STATUS_FEC_ENABLE_LIVE, 1);
> +	if (!ret)
> +		drm_dbg_kms(&i915->drm,
> +			    "Timeout waiting for FEC live state to get enabled"); }
> +
> +static void wait_for_fec_detected_with_retry(struct intel_encoder *encoder,
> +					     const struct intel_crtc_state
> *crtc_state,
> +					     struct drm_dp_aux *aux)
> +{
> +	struct drm_i915_private *i915 = to_i915(aux->drm_dev);
> +	int status;
> +	int err;
> +	int retrycount = 0;
> +
> +	do {
> +		err = readx_poll_timeout(read_fec_detected_status, aux,
> status,
> +					 status &
> DP_FEC_DECODE_EN_DETECTED || status < 0,
> +					 500, 5000);
> +
> +		if (!err && status >= 0)
> +			return;
> +
> +		if (err == -ETIMEDOUT) {
> +			drm_dbg_kms(&i915->drm,
> +				    "Timeout waiting for FEC ENABLE to get
> detected, retrying\n");
> +			retry_fec_enable(encoder, crtc_state, aux);
> +		} else {
> +			drm_dbg_kms(&i915->drm, "FEC detected status read
> error: %d\n", status);
> +		}
> +	} while (retrycount++ < FEC_RETRY_COUNT);
> +
> +	drm_err(&i915->drm, "FEC enable Failed after Retry\n"); }
> +
>  static void wait_for_fec_detected(struct drm_dp_aux *aux, bool enabled)  {
>  	struct drm_i915_private *i915 = to_i915(aux->drm_dev); @@ -2303,8
> +2356,12 @@ void intel_ddi_wait_for_fec_status(struct intel_encoder
> *encoder,
>  	 * At least the Synoptics MST hub doesn't set the detected flag for
>  	 * FEC decoding disabling so skip waiting for that.
>  	 */
> -	if (enabled)
> -		wait_for_fec_detected(&intel_dp->aux, enabled);
> +	if (enabled) {
> +		if (DISPLAY_VER(i915) >= 30)
> +			wait_for_fec_detected_with_retry(encoder, crtc_state,
> &intel_dp->aux);

wait_for_fec_detected_with_retry() should be called inside intel_ddi_enable_fec() after configuring DP_TP_CTL register and before transcoder is enabled.
wait_for_fec_detected() is called after transcoder is enabled.

> +		else
> +			wait_for_fec_detected(&intel_dp->aux, enabled);
> +	}
>  }
> 
>  static void intel_ddi_enable_fec(struct intel_encoder *encoder,
> --
> 2.25.1