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

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 23 Sep 2024, Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com> wrote:
> 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@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

If there's only one user, I wouldn't bother with a macro.

> +
>  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;
> +
> +	/* 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);

Please use a regular for loop with for (i = 0; i < N; i++) so even I can
look at it and know in an instant how many times it's going to loop.

> +
> +	drm_err(&i915->drm, "FEC enable Failed after Retry\n");
> +}
> +

There's just way, way too much duplication between the above two
functions and the existing intel_ddi_wait_for_fec_status() and
wait_for_fec_detected(). We'll want *one* code path with the retry baked
in, with no retries for older platforms.

BR,
Jani.


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

-- 
Jani Nikula, Intel