@@ -80,6 +80,11 @@ void radeon_connector_hotplug(struct drm_connector *connector)
if (!radeon_hpd_sense(rdev, radeon_connector->hpd.hpd)) {
drm_helper_connector_dpms(connector, DRM_MODE_DPMS_OFF);
} else if (radeon_dp_needs_link_train(radeon_connector)) {
+ /* Don't try to start link training before we
+ * have the dpcd */
+ if (!radeon_dp_getdpcd(radeon_connector))
+ return;
+
/* set it to OFF so that drm_helper_connector_dpms()
* won't return immediately since the current state
* is ON at this point.
This is a note to let you know that I have just added a patch titled DRM - radeon: Don't link train DisplayPort on HPD until we get the dpcd to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue This patch is scheduled to be released in version 3.13.11-ckt28. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.13.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ------ From a18b099362473bebf1bb3ffc45dfca9f9cdfc459 Mon Sep 17 00:00:00 2001 From: Stephen Chandler Paul <cpaul@redhat.com> Date: Fri, 21 Aug 2015 14:16:12 -0400 Subject: DRM - radeon: Don't link train DisplayPort on HPD until we get the dpcd commit 924f92bf12bfbef3662619e3ed24a1cea7c1cbcd upstream. Most of the time this isn't an issue since hotplugging an adaptor will trigger a crtc mode change which in turn, causes the driver to probe every DisplayPort for a dpcd. However, in cases where hotplugging doesn't cause a mode change (specifically when one unplugs a monitor from a DisplayPort connector, then plugs that same monitor back in seconds later on the same port without any other monitors connected), we never probe for the dpcd before starting the initial link training. What happens from there looks like this: - GPU has only one monitor connected. It's connected via DisplayPort, and does not go through an adaptor of any sort. - User unplugs DisplayPort connector from GPU. - Change in HPD is detected by the driver, we probe every DisplayPort for a possible connection. - Probe the port the user originally had the monitor connected on for it's dpcd. This fails, and we clear the first (and only the first) byte of the dpcd to indicate we no longer have a dpcd for this port. - User plugs the previously disconnected monitor back into the same DisplayPort. - radeon_connector_hotplug() is called before everyone else, and tries to handle the link training. Since only the first byte of the dpcd is zeroed, the driver is able to complete link training but does so against the wrong dpcd, causing it to initialize the link with the wrong settings. - Display stays blank (usually), dpcd is probed after the initial link training, and the driver prints no obvious messages to the log. In theory, since only one byte of the dpcd is chopped off (specifically, the byte that contains the revision information for DisplayPort), it's not entirely impossible that this bug may not show on certain monitors. For instance, the only reason this bug was visible on my ASUS PB238 monitor was due to the fact that this monitor using the enhanced framing symbol sequence, the flag for which is ignored if the radeon driver thinks that the DisplayPort version is below 1.1. Signed-off-by: Stephen Chandler Paul <cpaul@redhat.com> Reviewed-by: Jerome Glisse <jglisse@redhat.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- drivers/gpu/drm/radeon/radeon_connectors.c | 5 +++++ 1 file changed, 5 insertions(+) -- 1.9.1