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[2001:14ba:a0c3:3a00::55f]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-55a31a9b7c0sm357341e87.10.2025.07.18.11.30.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 18 Jul 2025 11:30:55 -0700 (PDT) Message-ID: <0bb0c437-e680-4160-b98f-efb816c9f049@oss.qualcomm.com> Date: Fri, 18 Jul 2025 21:30:54 +0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 6/9] drm/msm/dp: Work around bogus maximum link rate To: =?UTF-8?Q?J=C3=A9r=C3=B4me_de_Bretagne?= Cc: Konrad Dybcio , Xilin Wu , Dale Whinham , Rob Clark , Abhinav Kumar , Dmitry Baryshkov , Sean Paul , Marijn Suijten , David Airlie , Simona Vetter , linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20250714173554.14223-1-daleyo@gmail.com> <20250714173554.14223-7-daleyo@gmail.com> Content-Language: en-US From: Dmitry Baryshkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNzE4MDE0NyBTYWx0ZWRfX7ZXSInJ1tSNa rDdoDEKeoEbTe+jgy3zT4pC25598nYb5hZ5yuoVoy0zelTuVIvJXX67ozfuTber2kjtCKzof1Xc AaA7sIR1Jn8VSRWj/2AnR039kxnQboj+StwOZnkFCAxBcQXlvh1DwA2dKnJR4Zi1c6wgvzRJ0GW vMqJJ/yMiMMgagfGLbixW2CrW7WU/1uymjQva1edFEH17qV9u+JDCJ8/zPLA2qmINv35rEeL5OX XEx7Am/60S4mO8T/rRlZLg4/1t/CrILNiGD9cr2IzGJnJs5eHoJ+50kOvDXTMAj6cxIqMF4O76i xYpML8E1ocbXqnMvblN7gq//ImR89E0v9FLy5nyEDGINfSHwCV4Ly2QEgp4MdIXCaSI4H4N6/zg g0ZIx/upipSHlvgtNGQdAcUGDLNylbDRfN5tAH5H+wVHp8fSMuY+lWvQpKKwCFYC6UWbfOSa X-Proofpoint-GUID: Bdl6V5mPCP8oKK5tEPxMt5dhqqPWkPFQ X-Proofpoint-ORIG-GUID: Bdl6V5mPCP8oKK5tEPxMt5dhqqPWkPFQ X-Authority-Analysis: v=2.4 cv=Y+r4sgeN c=1 sm=1 tr=0 ts=687a92e2 cx=c_pps a=UbhLPJ621ZpgOD2l3yZY1w==:117 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=Wb1JkmetP80A:10 a=NEAV23lmAAAA:8 a=EUspDBNiAAAA:8 a=ksxQWNrZAAAA:8 a=pGLkceISAAAA:8 a=t_Of-uX1f6KDt8Xra0EA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=TOPH6uDL9cOC6tEoww4z:22 a=l7WU34MJF0Z5EO9KEJC3:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-07-18_04,2025-07-17_02,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 mlxlogscore=999 phishscore=0 malwarescore=0 priorityscore=1501 adultscore=0 impostorscore=0 mlxscore=0 suspectscore=0 lowpriorityscore=0 bulkscore=0 spamscore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505280000 definitions=main-2507180147 On 18/07/2025 21:26, Jérôme de Bretagne wrote: > On Friday, Jul 18, 2025, Dmitry Baryshkov > wrote: >> >> On Thu, Jul 17, 2025 at 11:36:38PM +0200, Jérôme de Bretagne wrote: >>> Le jeu. 17 juil. 2025 à 23:10, Konrad Dybcio >>> a écrit : >>>> >>>> On 7/17/25 10:27 PM, Jérôme de Bretagne wrote: >>>>> On 2025/7/17 04:21, Xilin Wu wrote : >>>>>> >>>>>> On 2025/7/15 01:35:42, Dale Whinham wrote: >>>>>>> From: Jérôme de Bretagne >>>>>>> >>>>>>> The OLED display in the Surface Pro 11 reports a maximum link rate of >>>>>>> zero in its DPCD, causing it to fail to probe correctly. >>>>>>> >>>>>>> The Surface Pro 11's DSDT table contains some XML with an >>>>>>> "EDPOverrideDPCDCaps" block that defines the max link rate as 0x1E >>>>>>> (8.1Gbps/HBR3). >>>>>>> >>>>>>> Add a quirk to conditionally override the max link rate if its value >>>>>>> is zero specifically for this model. >>>>>>> >>>>>>> Signed-off-by: Jérôme de Bretagne >>>>>>> Signed-off-by: Dale Whinham >>>>>>> --- >>>>>>> drivers/gpu/drm/msm/dp/dp_panel.c | 13 +++++++++++++ >>>>>>> 1 file changed, 13 insertions(+) >>>>>>> >> >> [...] >> >>> >>>>> >>>>> Is it a feature planned in the short-medium term within the MSM driver? >>>>> If not, would a quirk like [4] be acceptable upstream in the meanwhile? >>>> >>>> I'm not a display guy, but this looks like yet another block of code >>>> begging to be commonized across DP drivers, >>> >>> I agree 100% in principle, but the 3 implementations are different today. >>> >>>> so I wouldn't expect it to be a big blocker. >>> >>> Well, it is for me :) >>> >>>> Adding a panel quirk doesn't seem in order, as the panel is /probably/ >>>> very much in spec, and it's the driver bit that's missing. >>> >>> I agree that a quirk shouldn't be needed. I guess we'll work on >>> upstreaming everything else and keep an out-of-tree patch for this >>> issue for the moment That's a bit sad as this will block regular >>> users from easily installing / testing via the Ubuntu Concept ISO >>> for instance. >>> >>> Or could the quirk be accepted temporarily with good comments >>> then reverted when the driver adds the missing support? I guess >>> it would depend on the time scale of this support landing. >> >> Unforutunately, there is more than that. We should also be writing the >> LINK_RATE_SET register. So, just setting the max_bw is not enough. > > Maybe I've misunderstood. When you say max_bw is not enough, > are you talking about some future driver changes or about a potential > shorter-term fix? > > I can confirm that this initial simple patch (and also the updated one > reusing the quirk list [4]) is enough to get the SP11 OLED display > working whereas it doesn't probe and remains off without such a fix. These parts were changed in eDP 1.4 and then 1.5, but basically, if MAX_LINK_RATE is 0, the driver should also write LINK_RATE_SET register. See how it's handled by the intel or AMD drivers. > > Thanks, > Jérôme > > [4] https://github.com/JeromeDeBretagne/linux-surface-pro-11/commit/d265cfb >> -- >> With best wishes >> Dmitry -- With best wishes Dmitry