On 4/1/2015 11:23 AM, Ville Syrjälä wrote:
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@xxxxxxxxx>
---
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.
Yeah I had to squish it in there to keep it under 80 columns. Needs the
'*' on the left side too though. I'll fix that and repost.
+ 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?
As I recall, previous review feedback indicated that the timeout
condition there was already accounted for.
on 12/15, Paulo commented:
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?
When I checked the BSpec, that seemed to be the case so I removed the
TIME_OUT_ERROR. Without this
code in place, we still pass the compliance tests for AUX transactions,
one of which is for a no-reply transaction.
That case specifically should hit the TIME_OUT_ERROR if it was going to
occur, I would think.
If you can give me a case where that becomes an issue, it's a simple fix
to add it back in there.
if (status & DP_AUX_CH_CTL_DONE)
break;
}
--
1.9.1
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