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

[Borah, Chaitanya Kumar]

Hello Jani,

Thank you for the review.

> -----Original Message-----
> From: Jani Nikula <jani.nikula at linux.intel.com>
> Sent: Monday, September 23, 2024 12:40 PM
> To: Borah, Chaitanya Kumar <chaitanya.kumar.borah at intel.com>; intel-
> gfx at lists.freedesktop.org; intel-xe at lists.freedesktop.org
> Subject: Re: [PATCH] drm/i915/dp: Add FEC Enable Retry mechanism
> 
> On Mon, 23 Sep 2024, Chaitanya Kumar Borah
> <chaitanya.kumar.borah at 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 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
> 
> If there's only one user, I wouldn't bother with a macro.
> 

Ack.

> > +
> >  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.

Agreed. Let me try to cook something up.

Regards

Chaitanya

> 
> 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