From patchwork Wed Jun 1 18:23:24 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Doug Anderson X-Patchwork-Id: 12867148 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D5B10CCA473 for ; Wed, 1 Jun 2022 18:23:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235789AbiFASXe (ORCPT ); Wed, 1 Jun 2022 14:23:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40268 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232776AbiFASXd (ORCPT ); Wed, 1 Jun 2022 14:23:33 -0400 Received: from mail-pl1-x62c.google.com (mail-pl1-x62c.google.com [IPv6:2607:f8b0:4864:20::62c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2C586A0D2B for ; Wed, 1 Jun 2022 11:23:32 -0700 (PDT) Received: by mail-pl1-x62c.google.com with SMTP id o17so2527532pla.6 for ; Wed, 01 Jun 2022 11:23:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=/JhQL6K3uh3O984WIozZ8SgUhIwo1E2fCaDixGouuFc=; b=bQe+znboLg5KVUPXFanhDzZUyTtd8/DqaO3vDJEG8jvos5lAcS8YRMPwR4YULDJXsj VUwdHTs5Rva3cnmIkL6+hJJYk5zczz5bB21jHPGfDzUxQeai6Mz3pg6hyEPKCZRlKVL6 8XfbVXwlYmCQe4tsOJqMV7rgw065OFTvi1l/I= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=/JhQL6K3uh3O984WIozZ8SgUhIwo1E2fCaDixGouuFc=; b=287BUXf1bG7ZDarfSW1vuJD/XWi2CgGh8WMH1sZAaoC5T20bWsSh4RiuJYVPojCAjc VxnmzhCiw1j74RyayMurAa0qUruga+7G3q9A4KHYSN337rjor8L0JcNcp6Gr9BHaRN4F s7F47K35xGMWWEkhfmpFQ9GN3GyzU/xdHFJpsXCWn3QXPqYlx7+7ToWKzSNr17a2z1GK IltEKCP+lLymvRJ9vq5xkJ3fO/QCVe7CQf79a21dM5Atuu7qgBUYkrk0sh3KUcj2XNbu A85lTY1C3pJUg4HThlQh1vol3QpoZTO3O1acgN8ub7tj+r4KUBIxHm7M4ADB2+SkYQGD HM0w== X-Gm-Message-State: AOAM531pkNJhBOf4liwR0RWr57M9EGECG1yoL/WZQ1ZqslBEcR8ETsMb AWW+f3t/BgpiHV0VCXIvucWtJw== X-Google-Smtp-Source: ABdhPJxkZcEEXs4C3T4YbCZSNWjdVM2FImDp58YVkoQ7Y7Nye2+tmcgRAy4DLVeQEFjt+JV58ido0A== X-Received: by 2002:a17:90b:33ca:b0:1dc:e5b8:482b with SMTP id lk10-20020a17090b33ca00b001dce5b8482bmr35533108pjb.165.1654107811654; Wed, 01 Jun 2022 11:23:31 -0700 (PDT) Received: from tictac2.mtv.corp.google.com ([2620:15c:202:201:2f43:87c7:551a:ca93]) by smtp.gmail.com with ESMTPSA id ie12-20020a17090b400c00b001e2f0333a86sm1702300pjb.12.2022.06.01.11.23.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jun 2022 11:23:31 -0700 (PDT) From: Douglas Anderson To: dri-devel@lists.freedesktop.org, Daniel Vetter Cc: dmitry.baryshkov@linaro.org, tzimmermann@suse.de, linux-arm-msm@vger.kernel.org, swboyd@chromium.org, ville.syrjala@linux.intel.com, quic_sbillaka@quicinc.com, quic_khsieh@quicinc.com, quic_abhinavk@quicinc.com, robdclark@gmail.com, freedreno@lists.freedesktop.org, jani.nikula@linux.intel.com, quic_aravindh@quicinc.com, Douglas Anderson , David Airlie , Maarten Lankhorst , Maxime Ripard , linux-kernel@vger.kernel.org Subject: [PATCH v4] drm/probe-helper: Default to 640x480 if no EDID on DP Date: Wed, 1 Jun 2022 11:23:24 -0700 Message-Id: <20220601112302.v4.1.I31ec454f8d4ffce51a7708a8092f8a6f9c929092@changeid> X-Mailer: git-send-email 2.36.1.255.ge46751e96f-goog MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org If we're unable to read the EDID for a display because it's corrupt / bogus / invalid then we'll add a set of standard modes for the display. Since we have no true information about the connected display, these modes are essentially guesses but better than nothing. At the moment, none of the modes returned is marked as preferred, but the modes are sorted such that the higher resolution modes are listed first. When userspace sees these modes presented by the kernel it needs to figure out which one to pick. At least one userspace, ChromeOS [1] seems to use the rules (which seem pretty reasonable): 1. Try to pick the first mode marked as preferred. 2. Try to pick the mode which matches the first detailed timing descriptor in the EDID. 3. If no modes were marked as preferred then pick the first mode. Unfortunately, userspace's rules combined with what the kernel is doing causes us to fail section 4.2.2.6 (EDID Corruption Detection) of the DP 1.4a Link CTS. That test case says that, while it's OK to allow some implementation-specific fall-back modes if the EDID is bad that userspace should _default_ to 640x480. Let's fix this by marking 640x480 as default for DP in the no-EDID case. NOTES: - In the discussion around v3 of this patch [2] there was talk about solving this in userspace and I even implemented a patch that would have solved this for ChromeOS, but then the discussion turned back to solving this in the kernel. - Also in the discussion of v3 [2] it was requested to limit this 83;40900;0c change to just DP since folks were worried that it would break some subtle corner case on VGA or HDMI. [1] https://source.chromium.org/chromium/chromium/src/+/a051f741d0a15caff2251301efe081c30e0f4a96:ui/ozone/platform/drm/common/drm_util.cc;l=488 [2] https://lore.kernel.org/r/20220513130533.v3.1.I31ec454f8d4ffce51a7708a8092f8a6f9c929092@changeid Signed-off-by: Douglas Anderson Reviewed-by: Abhinav Kumar Reviewed-by: Sean Paul Reviewed-by: Dmitry Baryshkov Acked-by: Jani Nikula --- I put Abhinav's Reviewed-by tag from v2 here since this is nearly the same as v2. Hope this is OK. Changes in v4: - Code is back to v2, but limit to just DP. - Beefed up the commit message. Changes in v3: - Don't set preferred, just disable the sort. Changes in v2: - Don't modify drm_add_modes_noedid() 'cause that'll break others - Set 640x480 as preferred in drm_helper_probe_single_connector_modes() drivers/gpu/drm/drm_probe_helper.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c index 425f56280d51..75a71649b64d 100644 --- a/drivers/gpu/drm/drm_probe_helper.c +++ b/drivers/gpu/drm/drm_probe_helper.c @@ -569,8 +569,17 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector, count = drm_add_override_edid_modes(connector); if (count == 0 && (connector->status == connector_status_connected || - connector->status == connector_status_unknown)) + connector->status == connector_status_unknown)) { count = drm_add_modes_noedid(connector, 1024, 768); + + /* + * Section 4.2.2.6 (EDID Corruption Detection) of the DP 1.4a + * Link CTS specifies that 640x480 (the official "failsafe" + * mode) needs to be the default if there's no EDID. + */ + if (connector->connector_type == DRM_MODE_CONNECTOR_DisplayPort) + drm_set_preferred_mode(connector, 640, 480); + } count += drm_helper_probe_add_cmdline_mode(connector); if (count != 0) { ret = __drm_helper_update_and_validate(connector, maxX, maxY, &ctx);