Re: [PATCH 4/4] drm/i915/psr: Account for sink CRC raciness on some panels

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

On Sat, 06 May 2017, Jim Bride <jim.bride@linux.intel.com> wrote:
> According to the eDP spec, when the count field in TEST_SINK_MISC
> increments then the six bytes of sink CRC information in the DPCD
> should be valid.  Unfortunately, this doesn't seem to be the case
> on some panels, and as a result we get some incorrect and inconsistent
> values from the sink CRC DPCD locations at times.  This problem exhibits
> itself more on faster processors (relative failure rates HSW < SKL < KBL.)
> In order to try and account for this, we try a lot harder to read the sink
> CRC until we get consistent values twice in a row before returning what we
> read and delay for a time before trying to read.  We still see some
> occasional failures, but reading the sink CRC is much more reliable,
> particularly on SKL and KBL, with these changes than without.

Retrying seems like a good idea. But this patch retries up to 36 times
if the two consecutive reads don't match, which is excessive.

The sleeps should probably be a separate change. Also not happy about
the magic numbers there.

Also, there are plenty of what seem like unrelated changes. Whitespace,
debug logging, error checking, etc.


BR,
Jani.


>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
> Signed-off-by: Jim Bride <jim.bride@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c | 14 +++++++--
>  drivers/gpu/drm/i915/intel_dp.c     | 57 ++++++++++++++++++++++++++++++++-----
>  2 files changed, 61 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 870c470..4902473 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -2718,7 +2718,7 @@ static int i915_sink_crc(struct seq_file *m, void *data)
>  	struct intel_connector *connector;
>  	struct drm_connector_list_iter conn_iter;
>  	struct intel_dp *intel_dp = NULL;
> -	int ret;
> +	int ret, tries = 6;
>  	u8 crc[6];
>  
>  	drm_modeset_lock_all(dev);
> @@ -2738,9 +2738,17 @@ static int i915_sink_crc(struct seq_file *m, void *data)
>  
>  		intel_dp = enc_to_intel_dp(connector->base.state->best_encoder);
>  
> -		ret = intel_dp_sink_crc(intel_dp, crc);
> -		if (ret)
> +		memset(crc, 0, 6);
> +		do {
> +			ret = intel_dp_sink_crc(intel_dp, crc);
> +			if (ret == -ETIMEDOUT)
> +				usleep_range(500, 700);
> +		} while ((ret == -ETIMEDOUT) && --tries);
> +
> +		if (ret != 0) {
> +			seq_printf(m, "000000000000\n");
>  			goto out;
> +		}
>  
>  		seq_printf(m, "%02x%02x%02x%02x%02x%02x\n",
>  			   crc[0], crc[1], crc[2],
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 06b8bd4..217bc06 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -3877,13 +3877,15 @@ static int intel_dp_sink_crc_stop(struct intel_dp *intel_dp)
>  
>  	do {
>  		intel_wait_for_vblank(dev_priv, intel_crtc->pipe);
> -
> +		usleep_range(16700, 17000);
>  		if (drm_dp_dpcd_readb(&intel_dp->aux,
>  				      DP_TEST_SINK_MISC, &buf) < 0) {
> +			DRM_DEBUG_KMS("Could not read TEST_SINK_MISC\n");
>  			ret = -EIO;
>  			goto out;
>  		}
>  		count = buf & DP_TEST_COUNT_MASK;
> +		DRM_DEBUG_KMS("PSR count is %d\n", count);
>  	} while (--attempts && count);
>  
>  	if (attempts == 0) {
> @@ -3928,6 +3930,8 @@ static int intel_dp_sink_crc_start(struct intel_dp *intel_dp)
>  	}
>  
>  	intel_wait_for_vblank(dev_priv, intel_crtc->pipe);
> +	usleep_range(16700, 17000);
> +	DRM_DEBUG_KMS("PSR Successfully started sink CRC\n");
>  	return 0;
>  }
>  
> @@ -3939,21 +3943,30 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
>  	u8 buf;
>  	int count, ret;
>  	int attempts = 6;
> +	u8 old_crc[6];
> +
> +	if (crc != NULL)
> +		memset(crc, 0, 6);
> +	else
> +		return -ENOMEM;
>  
>  	ret = intel_dp_sink_crc_start(intel_dp);
> -	if (ret)
> +	if (ret) {
> +		DRM_DEBUG_KMS("Could not start sink crc; ret %d\n", ret);
>  		return ret;
> +	}
>  
>  	do {
>  		intel_wait_for_vblank(dev_priv, intel_crtc->pipe);
> +		usleep_range(16700, 17000);
>  
>  		if (drm_dp_dpcd_readb(&intel_dp->aux,
>  				      DP_TEST_SINK_MISC, &buf) < 0) {
> +			DRM_DEBUG_KMS("Cound not read TEST_SINK_MISC\n");
>  			ret = -EIO;
>  			goto stop;
>  		}
>  		count = buf & DP_TEST_COUNT_MASK;
> -
>  	} while (--attempts && count == 0);
>  
>  	if (attempts == 0) {
> @@ -3962,11 +3975,41 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
>  		goto stop;
>  	}
>  
> -	if (drm_dp_dpcd_read(&intel_dp->aux, DP_TEST_CRC_R_CR, crc, 6) < 0) {
> -		ret = -EIO;
> -		goto stop;
> -	}
> +	attempts = 6;
> +	memset(old_crc, 0xFF, 6);
> +	do {
> +		intel_wait_for_vblank(dev_priv, intel_crtc->pipe);
> +		usleep_range(16500, 17000);
> +		if (drm_dp_dpcd_read(&intel_dp->aux, DP_TEST_CRC_R_CR,
> +				     crc, 6) < 0) {
> +			DRM_DEBUG_KMS("Could not read sink crc\n");
> +			ret = -EIO;
> +			goto stop;
> +		}
> +
> +		if (memcmp(old_crc, crc, 6) == 0) {
> +			DRM_DEBUG_KMS("PSR Active: %3s Matching crc values found:"
> +				      "%02x%02x%02x%02x%02x%02x\n",
> +				      yesno(dev_priv->psr.active),
> +				      crc[0], crc[1], crc[2],
> +				      crc[3], crc[4], crc[5]);
> +			ret = 0;
> +			goto stop;
> +		} else {
> +			DRM_DEBUG_KMS("PSR Active: %3s crc %02x%02x%02x%02x%02x%02x "
> +				      "doesn't match "
> +				      "previous %02x%02x%02x%02x%02x%02x\n",
> +				      yesno(dev_priv->psr.active),
> +				      crc[0], crc[1], crc[2],
> +				      crc[3], crc[4], crc[5],
> +				      old_crc[0], old_crc[1], old_crc[2],
> +				      old_crc[3], old_crc[4], old_crc[5]);
> +			memcpy(old_crc, crc, 6);
> +		}
> +	} while (--attempts);
>  
> +	DRM_DEBUG_KMS("Failed to get CRC after 6 attempts.\n");
> +	ret = -ETIMEDOUT;
>  stop:
>  	intel_dp_sink_crc_stop(intel_dp);
>  	return ret;

-- 
Jani Nikula, Intel Open Source Technology Center
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