Re: [PATCH 03/17] drm/i915: Add a delay in Displayport AUX transactions for compliance testing

Paulo Zanoni
2014-12-15T17:35:00Z

2014-12-10 21:53 GMT-02:00 Todd Previte <tprevite@gmail.com>:
> 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()
>
> Signed-off-by: Todd Previte <tprevite@gmail.com>
> ---
> drivers/gpu/drm/i915/intel_dp.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 1b452cc..b6f5a72 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -876,9 +876,14 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
> DP_AUX_CH_CTL_TIME_OUT_ERROR |
> DP_AUX_CH_CTL_RECEIVE_ERROR);
>
> + /* DP compliance requires 400us delay for errors
> + and timeouts (DP CTS 1.2 Core Rev 1.1, 4.2.1.1
> + & 4.2.1.2) */
> if (status & (DP_AUX_CH_CTL_TIME_OUT_ERROR |
> - DP_AUX_CH_CTL_RECEIVE_ERROR))
> + DP_AUX_CH_CTL_RECEIVE_ERROR)) {
> + usleep_range(400, 500);

One thing to notice is that if we get a TIME_OUT_ERROR I guess it
means we already waited our standard timeout (which is either 400, 600
or 1600, depending on the platform), so shouldn't we just do the
usleep() after the RECEIVE_ERROR error?

> continue;
> + }
> if (status & DP_AUX_CH_CTL_DONE)
> break;
> }
> --
> 1.9.1
>
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--
Paulo Zanoni