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Thu, 4 Sep 2025 21:48:17 +0000 Date: Fri, 5 Sep 2025 00:48:11 +0300 From: Imre Deak To: Greg Kroah-Hartman CC: , , , , "Sasha Levin" Subject: Re: [PATCH 6.16 139/142] Revert "drm/dp: Change AUX DPCD probe address from DPCD_REV to LANE0_1_STATUS" Message-ID: Reply-To: References: <20250902131948.154194162@linuxfoundation.org> <20250902131953.603872091@linuxfoundation.org> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20250902131953.603872091@linuxfoundation.org> X-ClientProxiedBy: DB9PR06CA0001.eurprd06.prod.outlook.com (2603:10a6:10:1db::6) To SJ0PR11MB4845.namprd11.prod.outlook.com (2603:10b6:a03:2d1::10) Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ0PR11MB4845:EE_|IA4PR11MB9153:EE_ X-MS-Office365-Filtering-Correlation-Id: 2168bd48-8eaa-4f8d-429a-08ddebfcc193 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|10070799003|1800799024|376014|366016|7053199007; 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If anyone has any objections, please let me know. Thanks for queuing this and the corresponding reverts for the other stable trees. This one patch doesn't match what I sent, the address should be changed to DP_TRAINING_PATTERN_SET not to DP_DPCD_REV, see [1]. I still think that's the correct thing to do here conforming to the DP Standard and matching what the upstream kernel does, also solving a link training issue for a DP2.0 docking station. The reverts queued for the other stable trees are correct, since for now I do not want to change the behavior in those (i.e. those trees should continue to use the DP_DPCD_REV register matching what's been the case since the DPCD probing was introduced). Thanks, Imre [1] https://lore.kernel.org/all/20250828174932.414566-7-imre.deak@intel.com > ------------------ > > From: Imre Deak > > This reverts commit 944e732be9c3a33e64e9fb0f5451a37fc252ddfc which is > commit a40c5d727b8111b5db424a1e43e14a1dcce1e77f upstream. > > The upstream commit a40c5d727b8111b5db424a1e43e14a1dcce1e77f ("drm/dp: > Change AUX DPCD probe address from DPCD_REV to LANE0_1_STATUS") the > reverted commit backported causes a regression, on one eDP panel at > least resulting in display flickering, described in detail at the Link: > below. The issue fixed by the upstream commit will need a different > solution, revert the backport for now. > > Cc: intel-gfx@lists.freedesktop.org > Cc: dri-devel@lists.freedesktop.org > Cc: Sasha Levin > Link: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14558 > Signed-off-by: Imre Deak > Signed-off-by: Greg Kroah-Hartman > --- > drivers/gpu/drm/display/drm_dp_helper.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- a/drivers/gpu/drm/display/drm_dp_helper.c > +++ b/drivers/gpu/drm/display/drm_dp_helper.c > @@ -725,7 +725,7 @@ ssize_t drm_dp_dpcd_read(struct drm_dp_a > * monitor doesn't power down exactly after the throw away read. > */ > if (!aux->is_remote) { > - ret = drm_dp_dpcd_probe(aux, DP_LANE0_1_STATUS); > + ret = drm_dp_dpcd_probe(aux, DP_DPCD_REV); > if (ret < 0) > return ret; > } > >