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Thu, 3 Jul 2025 15:30:16 +0000 Date: Thu, 3 Jul 2025 18:30:09 +0300 From: Imre Deak To: Greg Kroah-Hartman CC: , , Ville =?iso-8859-1?Q?Syrj=E4l=E4?= , Jani Nikula , Jani Nikula , "Joonas Lahtinen" Subject: Re: [PATCH 6.1 075/132] drm/dp: Change AUX DPCD probe address from DPCD_REV to LANE0_1_STATUS Message-ID: Reply-To: References: <20250703143939.370927276@linuxfoundation.org> <20250703143942.360601573@linuxfoundation.org> Content-Type: text/plain; charset="iso-8859-1" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250703143942.360601573@linuxfoundation.org> X-ClientProxiedBy: LO4P265CA0231.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:315::17) 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_|DM4PR11MB8178:EE_ X-MS-Office365-Filtering-Correlation-Id: 5756988c-fd70-4a02-a3a4-08ddba468297 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|366016|7053199007; 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So far I got a notification that the patch got queued for the 6.1, 6.6, 6.12, 6.15 stable trees, it should be removed from all. Sorry for the trouble this caused. Thanks, Imre On Thu, Jul 03, 2025 at 04:42:44PM +0200, Greg Kroah-Hartman wrote: > 6.1-stable review patch. If anyone has any objections, please let me know. > > ------------------ > > From: Imre Deak > > commit a3ef3c2da675a8a564c8bea1a511cdd0a2a9aa49 upstream. > > Reading DPCD registers has side-effects in general. In particular > accessing registers outside of the link training register range > (0x102-0x106, 0x202-0x207, 0x200c-0x200f, 0x2216) is explicitly > forbidden by the DP v2.1 Standard, see > > 3.6.5.1 DPTX AUX Transaction Handling Mandates > 3.6.7.4 128b/132b DP Link Layer LTTPR Link Training Mandates > > Based on my tests, accessing the DPCD_REV register during the link > training of an UHBR TBT DP tunnel sink leads to link training failures. > > Solve the above by using the DP_LANE0_1_STATUS (0x202) register for the > DPCD register access quirk. > > Cc: > Cc: Ville Syrjälä > Cc: Jani Nikula > Acked-by: Jani Nikula > Signed-off-by: Imre Deak > Link: https://lore.kernel.org/r/20250605082850.65136-2-imre.deak@intel.com > (cherry picked from commit a40c5d727b8111b5db424a1e43e14a1dcce1e77f) > Signed-off-by: Joonas Lahtinen > 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 > @@ -663,7 +663,7 @@ 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_DPCD_REV); > + ret = drm_dp_dpcd_probe(aux, DP_LANE0_1_STATUS); > if (ret < 0) > return ret; > } > >