Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752093AbbHUSRK (ORCPT ); Fri, 21 Aug 2015 14:17:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42090 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751344AbbHUSRI (ORCPT ); Fri, 21 Aug 2015 14:17:08 -0400 From: cpaul@redhat.com To: Alex Deucher , =?UTF-8?q?Christian=20K=C3=B6nig?= , David Airlie , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: Jerome Glisse , Benjamin Tissoires Subject: [PATCH] DRM - radeon: Don't link train DisplayPort on HPD until we get the dpcd Date: Fri, 21 Aug 2015 14:16:12 -0400 Message-Id: <1440180972-29580-1-git-send-email-cpaul@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3305 Lines: 75 From: Stephen Chandler Paul 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 Reviewed-by: Jerome Glisse --- drivers/gpu/drm/radeon/radeon_connectors.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/gpu/drm/radeon/radeon_connectors.c b/drivers/gpu/drm/radeon/radeon_connectors.c index 94b21ae..5a2cafb 100644 --- a/drivers/gpu/drm/radeon/radeon_connectors.c +++ b/drivers/gpu/drm/radeon/radeon_connectors.c @@ -95,6 +95,11 @@ 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. -- 2.4.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/