Re: [PATCH 2/6] drm/i915: Add a delay in Displayport AUX transactions for compliance testing

[Chris Wilson <chris@chris-wilson.co.uk>]

On Tue, Jun 24, 2014 at 03:12:50PM -0700, Todd Previte wrote:
> Several compliance tests require that follow-up AUX transactions (after a
> failure or no response) are not resent sooner than 400us later. Add a 400us
> delay to the response time of any failed transaction to account for this.
> 
> Signed-off-by: Todd Previte <tprevite@gmail.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 3bd1780..43fcabe 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -561,8 +561,12 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
>  				   DP_AUX_CH_CTL_RECEIVE_ERROR);
>  
>  			if (status & (DP_AUX_CH_CTL_TIME_OUT_ERROR |
> -				      DP_AUX_CH_CTL_RECEIVE_ERROR))
> +				      DP_AUX_CH_CTL_RECEIVE_ERROR)) {

I think "required for DP compliance testing" is a little verbose and can
be shortened to "DP requires". If you have a spec reference handy, that
would be useful.

/* 10.2.1: DP requires 400us delay after an error. */
> +				/* 400us delay between transactions for errors/timeouts
> +				   required for DP compliance testing */
> +				udelay(400);
>  				continue;
> +			}
>  			if (status & DP_AUX_CH_CTL_DONE)
>  				break;

-- 
Chris Wilson, Intel Open Source Technology Centre