[Intel-gfx] [PATCH 3/9] drm/i915: Add a delay in Displayport AUX transactions for compliance testing

[Ville Syrjälä]

On Tue, Mar 31, 2015 at 10:15:00AM -0700, Todd Previte wrote:
> The Displayport Link Layer Compliance Testing Specification 1.2 rev 1.1
> specifies that repeated AUX transactions after a failure (no response /
> invalid response) must have a minimum delay of 400us before the resend can
> occur. Tests 4.2.1.1 and 4.2.1.2 are two tests that require this specifically.
> 
> V2:
> - Changed udelay() to usleep_range()
> V3:
> - Removed extraneous check for timeout
> - Updated comment to reflect this change
> 
> Signed-off-by: Todd Previte <tprevite at gmail.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index ed2f60c..dc87276 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -877,9 +877,15 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
>  				   DP_AUX_CH_CTL_TIME_OUT_ERROR |
>  				   DP_AUX_CH_CTL_RECEIVE_ERROR);
>  
> -			if (status & (DP_AUX_CH_CTL_TIME_OUT_ERROR |
> -				      DP_AUX_CH_CTL_RECEIVE_ERROR))
> +			/* DP CTS 1.2 Core Rev 1.1, 4.2.1.1 & 4.2.1.2
> +			     400us delay required for errors and timeouts
> +			     Timeout errors from the HW already meet this
> +			     requirement so skip to next iteration
> +			*/

Weird format for multi line comment.

> +			if (status & DP_AUX_CH_CTL_RECEIVE_ERROR) {
> +				usleep_range(400, 500);
>  				continue;
> +			}

Where did the DP_AUX_CH_CTL_TIME_OUT_ERROR handling go?

>  			if (status & DP_AUX_CH_CTL_DONE)
>  				break;
>  		}
> -- 
> 1.9.1
> 
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-- 
Ville Syrjälä
Intel OTC