On 5/21/2015 1:28 AM, Jani Nikula wrote:
On Thu, 21 May 2015, Todd Previte <tprevite@xxxxxxxxx> wrote:
Passive DP->DVI/HDMI dongles show up to the system as HDMI devices, as they
do not have a sink device in them to respond to any AUX traffic. When
probing these dongles over the DDC, sometimes they will NAK the first attempt
even though the transaction is valid and they support the DDC protocol. The
retry loop inside of drm_do_probe_ddc_edid() would normally catch this case
and try the transaction again, resulting in success.
That, however, was thwarted by the fix for fdo.org bug #41059. The patch is:
commit 9292f37e1f5c79400254dca46f83313488093825
Author: Eugeni Dodonov <eugeni.dodonov@xxxxxxxxx>
Date: Thu Jan 5 09:34:28 2012 -0200
drm: give up on edid retries when i2c bus is not responding
Some extra background:
That commit refers to the i2c bit banging code, while i915 now prefers
gmbus, and only falls back to big banging on certain failures. (See
gmbux_xfer() in i915/intel_i2c.c). This means that in most cases i915 is
no longer susceptible to the 5*3 timeout loops, but it also means we
don't have the i2c bit banging retry at all on -ENXIO, like Todd notes.
The questions are, is one retry after -ENXIO in drm_do_probe_ddc_edid
enough now? Should we revert the original commit instead since the
underlying algorithm has changed? Or should we return something other
than -ENXIO from our gmbus code to not hit this exit with no retries
path?
Question #1:
During development and testing, all of the passive dongles used would
NAK once before operating correctly. I had an additional dongle here
that I tested as well and it exhibited the exact same behavior. While I
believe that more testing certainly needs to be done (as you mention
below) at this point I would say allowing a single NAK is sufficient to
solve this problem.
Question #2:
While I agree to some extent that this patch is dated with respect to
the underlying algorithm changes, there still appears to be some value
in keeping it since it does allow for more efficient processing of
disconnected ports. So I would recommend against reverting this commit
right now.
Question #3:
I'm looking into this now. I'll have more information by the end of the day.
This added code to exit immediately if the return code from the
i2c_transfer function was -ENXIO in order to reduce the amount of time spent
in waiting for unresponsive or disconnected devices. For the DP dongles,
this means that the second retry never happens which results in a failed
EDID probe and a black screen.
To work around this problem without undoing the fix for bug #41059, the
number of retries is checked along with the return code. This allows for a
device to NAK once and still continue operations. A second NAK will result
in breaking the loop as it would have before and stopping the DDC probe.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=85924
Maybe throw this at other dongle bugs you can find too?
We're going to need Tested-bys though.
BR,
Jani.
Definitely - I'll go wrangle up the dongle bugs I can find on kernel.org
and FDO and see if this affects them.
As for testing, the more the merrier on this front. If anyone has
passive DP->DVI/HDMI dongles and the ability to test them, please see
the bug Jani referenced above and report your findings there.
-T
Signed-off-by: Todd Previte <tprevite@xxxxxxxxx>
Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
---
drivers/gpu/drm/drm_edid.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 7087da3..e8047bd 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -1238,7 +1238,10 @@ drm_do_probe_ddc_edid(void *data, u8 *buf, unsigned int block, size_t len)
*/
ret = i2c_transfer(adapter, &msgs[3 - xfers], xfers);
- if (ret == -ENXIO) {
+ /* Passive DP->DVI/HDMI dongles sometimes NAK the first probe
+ * Try to probe again but if it NAKs, stop trying
+ */
+ if (ret == -ENXIO && retries < 5) {
DRM_DEBUG_KMS("drm: skipping non-existent adapter %s\n",
adapter->name);
break;
--
1.9.1
_______________________________________________
Intel-gfx mailing list
Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
http://lists.freedesktop.org/mailman/listinfo/intel-gfx
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
http://lists.freedesktop.org/mailman/listinfo/dri-devel
