[Intel-gfx] [PATCH 12/12] drm/i915: Add a delay in Displayport AUX transactions for compliance testing

[Daniel Vetter]

On Mon, Jul 14, 2014 at 12:10:47PM -0700, Todd Previte wrote:
> The Displayport Link Layer Compliance Testing Specification 1.2 rev 1.1 specifies that
> repeated AUX transactions after a failure (NACK, DEFER or no 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.
> 
> Signed-off-by: Todd Previte <tprevite at gmail.com>

Since this is a minimal timeout ... shouldn't we put it into the dp
helpers instead?
-Daniel

> ---
>  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 0e207aaf..f0664cd 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -573,8 +573,12 @@ 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)) {
> +				/* DP compliance requires 400us delay for errors/timeouts
> +				   (DP CTS 1.2 Core Rev 1.1, 4.2.1.1 & 4.2.1.2) */
> +				udelay(400);
>  				continue;
> +			}
>  			if (status & DP_AUX_CH_CTL_DONE)
>  				break;
>  		}
> -- 
> 1.9.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch