Attachment 115935 Details for Bug 85924 – Fix for passive DP->DVI/HDMI dongles

[patch] Fix for passive DP->DVI/HDMI dongles

0001-drm-edid-Fix-DDC-probe-for-passive-DP-dongles.patch (text/plain), 2.25 KB, created by Todd Previte on 2015-05-21 00:14:34 UTC

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Creator: Todd Previte

Created: 2015-05-21 00:14:34 UTC

Size: 2.25 KB

patch

obsolete

>From 358a91e9eb01e132a04b72406db81c9256f0ef07 Mon Sep 17 00:00:00 2001
>From: Todd Previte <tprevite@gmail.com>
>Date: Wed, 20 May 2015 14:28:49 -0700
>Subject: [PATCH] drm/edid: Fix DDC probe for passive DP dongles
>
>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@intel.com>
>	Date:   Thu Jan 5 09:34:28 2012 -0200
>
>	drm: give up on edid retries when i2c bus is not responding
>
>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.
>
>Signed-off-by: Todd Previte <tprevite@gmail.com>
>---
> 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 9ab1017..c17af3e 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
>

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Attachments on bug 85924: 108975 | 110305 | 113910 | 113911 | 113912 | 113913 | 114200 | 114201 | 114202 | 114203 | 114482 | 114724 | 115826 | 115935 | 116153

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