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[78.88.45.245]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ad89f2508b7sm8518366b.132.2025.05.27.13.49.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 May 2025 13:49:41 -0700 (PDT) Message-ID: Date: Tue, 27 May 2025 22:49:38 +0200 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 7/8] drm/msm/dp: Retry Link Training 2 with lower pattern To: Dmitry Baryshkov , Xiangxu Yin Cc: Rob Clark , Abhinav Kumar , Sean Paul , Marijn Suijten , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Kuogee Hsieh , Vinod Koul , Kishon Vijay Abraham I , Linus Walleij , Bartosz Golaszewski , quic_lliu6@quicinc.com, quic_fangez@quicinc.com, linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-phy@lists.infradead.org, linux-gpio@vger.kernel.org References: <20241129-add-displayport-support-for-qcs615-platform-v1-0-09a4338d93ef@quicinc.com> <20241129-add-displayport-support-for-qcs615-platform-v1-7-09a4338d93ef@quicinc.com> Content-Language: en-US From: Konrad Dybcio In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Proofpoint-GUID: Ka48idWdM7oFsSfO0hP3rGl2bMtaQlMM X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNTI3MDE3NiBTYWx0ZWRfX7GUXAFO8S+UN FRwz5+4DSGJJurS9bs3R3uefoNGFTMdaVXxBHf28tZXn7RHXxMz4VS5srIt892RuMS5Huz1C+ST EXhT8uJ+3SKwEQpCxLFuxPivXeeZVkFJoa35TAisx/drP0hVlK0q0qWKyFznSUa2uVfNJ12nPY9 w14+c4r3QnG3ixmHAoIQBWyWJa4zYvR/BQNwdAi2MwkwvI2/9dgrBIV81DeFAHkLEgeGPa2pfJh w1Gn152sgRTnz/56e6wPasi4Zuhp4Th7Qv1YqOd/Rzvu/zHXIcbZhMLWvYm45VBoHgM6Yjj4hS2 z9bHsvD7waPwVPNIdHMhpajD2EDtJhL7f+N3sRBdTWIsWuaTQXONASfZwvPpGvJQ0EaMPk4Ge3/ IV9yu1KZ/3G2XCe5AC1YiFWcVC1scOkljAuYkrw5nC5dyMjN/c0fNUSQxO77iYZ+LOMgRUOO X-Authority-Analysis: v=2.4 cv=fMk53Yae c=1 sm=1 tr=0 ts=68362568 cx=c_pps a=qKBjSQ1v91RyAK45QCPf5w==:117 a=FpWmc02/iXfjRdCD7H54yg==:17 a=IkcTkHD0fZMA:10 a=dt9VzEwgFbYA:10 a=COk6AnOGAAAA:8 a=OAqA0DyV7igbTOjjZJsA:9 a=QEXdDO2ut3YA:10 a=NFOGd7dJGGMPyQGDc5-O:22 a=TjNXssC_j7lpFel5tvFf:22 X-Proofpoint-ORIG-GUID: Ka48idWdM7oFsSfO0hP3rGl2bMtaQlMM X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.0.736,FMLib:17.12.80.40 definitions=2025-05-27_10,2025-05-27_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 adultscore=0 impostorscore=0 phishscore=0 suspectscore=0 spamscore=0 priorityscore=1501 lowpriorityscore=0 clxscore=1015 mlxscore=0 mlxlogscore=999 bulkscore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505160000 definitions=main-2505270176 On 12/3/24 3:07 PM, Dmitry Baryshkov wrote: > On Tue, Dec 03, 2024 at 04:13:22PM +0800, Xiangxu Yin wrote: >> >> >> On 11/29/2024 9:53 PM, Dmitry Baryshkov wrote: >>> On Fri, 29 Nov 2024 at 09:59, Xiangxu Yin wrote: >>>> >>>> Add a mechanism to retry Link Training 2 by lowering the pattern level >>>> when the link training #2 first attempt fails. This approach enhances >>>> compatibility, particularly addressing issues caused by certain hub >>>> configurations. >>> >>> Please reference corresponding part of the standard, describing this lowering. >>> >> Per DisplayPort 1.4a specification Section 3.5.1.2 and Table 3-10, while the standard doesn't explicitly define a TPS downgrade mechanism, it does specify: > > Anything in DP 2.1? > >> - All devices shall support TPS1 and TPS2 >> - HDR2-capable devices shall support TPS3 >> - HDR3-capable devices shall support TPS4 >> While these capabilities are explicitly defined DPCD for sink devices, source device capabilities are less strictly defined, with the minimum requirement being support for TPS1 and TPS2. >> In QCS615 DP phy is only supporting to HBR2, we observed a critical interoperability scenario with a DP->HDMI bridge. When link training at TPS4 consistently failed, downgrading to the next lower training pattern successfully established the link and display output successfully. > > Any other driver doing such TPS lowering? Or maybe we should be > selecting TPS3 for HBR2-only devices? Bump, this patch looks interesting and I'd like to see it revisited if it's correct Konrad