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Mon, 09 Nov 2026 20:14:44 -0800 (PST) Received: from [10.64.69.173] ([114.94.8.21]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2edb6d4d838sm4208715ad.12.2026.11.09.20.14.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 09 Nov 2026 20:14:43 -0800 (PST) Message-ID: <7c80e1ac-e4ed-40cb-b562-cc2a27e6bc3f@oss.qualcomm.com> Date: Tue, 10 Nov 2026 12:14:37 +0800 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 00/35] drm/msm/dp: Add MST support for MSM chipsets To: Dmitry Baryshkov , Robert Meijers Cc: abhinav.kumar@linux.dev, airlied@gmail.com, dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org, jesszhan0024@gmail.com, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, lumag@kernel.org, marijn.suijten@somainline.org, quic_abhinavk@quicinc.com, robin.clark@oss.qualcomm.com, sean@poorly.run, simona@ffwll.ch, stable@vger.kernel.org References: <20260929-msm-dp-mst-v7-0-4b81473185e7@oss.qualcomm.com> Content-Language: en-US From: Yongxing Mou In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Proofpoint-Spam-Info: AW1haW4tMjYxMTEwMDAxNiBTYWx0ZWRfX0YVf13M2YPHv Zeog366rKRuYjNtWt8hD94muDWB0+kP2vl7y9ELLLj82XihRn6naDYHZxsjqF2aumJG8RmOA+gV setDrmC8ugLrT5b4kbtxE6xrjvlAyMw= X-Proofpoint-ORIG-GUID: VFDY163QrThaBc3-Z-Bi3VL95mgap8fb X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTEwMDAxNiBTYWx0ZWRfX1de2nJ+hTT5Q zu3UvfzhNAK+qhhksCBN/toJK0/DyyBkT2ulS1puQ756faciLDrqw3SIDf2c+z4HGG0ZvO38L47 KPNajSnjtLR9149BS0nqDBsjCOLGyusdfgYdUVXOfJUhBr1TFvxB+SDvUbD6N4q8oPjLSMhNO4Z hwU1w2U2aYBRofuDw4NUZNzsCP0ICzGueU+sbEzZ+Af7+bC8DF2ukif2V2QpTxhj9XrWf60I3SL Sn6kS/SK0YxL2+HLwKUW47ucjF+7LXobj+TjVBLk4yveCNX+3aErrbb0qPQESikFPkIdYUs+56M 523+cMEO+C3bdrpHhEamDxXMT+yPYFzKbzurfkAq0tBvwrysdLw9FWC2q63DJnfA2AGDTshOw4f Q7A/3v3BqMQmYxlXzBeocW2VNPSX2s5n1aZrE86busDact18TD6/ABJ5ReU9NvJ7xcBmgN689f9 /gUqIg2DlEVv8vgCMgg== X-Authority-Analysis: v=2.4 cv=B54sQ+tM c=1 sm=1 tr=0 ts=6af29a35 cx=c_pps a=cmESyDAEBpBGqyK7t0alAg==:117 a=Uz3yg00KUFJ2y2WijEJ4bw==:17 a=IkcTkHD0fZMA:10 a=zJRp6_cAMcgA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=DJpcGTmdVt4CTyJn9g5Z:22 a=m0oZJYypAzi8eX9yTqQA:9 a=QEXdDO2ut3YA:10 a=1OuFwYUASf3TG4hYMiVC:22 X-Proofpoint-GUID: VFDY163QrThaBc3-Z-Bi3VL95mgap8fb X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-11-10_02,2026-11-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 priorityscore=1501 impostorscore=0 phishscore=0 bulkscore=0 malwarescore=0 adultscore=0 suspectscore=0 clxscore=1015 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2611040001 definitions=main-2611100016 On 11/9/2026 3:25 AM, Dmitry Baryshkov wrote: > On Tue, Oct 27, 2026 at 10:04:54PM +0100, Robert Meijers wrote: >> Hi, >> >> ((Sorry, re-sending because the first was rejected for not being plain >> text)) >> (First up this is the first time I'm participating on a mailing list, >> so sorry in advance if I'm doing something wrong). >> >>> Add support for Multi-stream transport for MSM chipsets that allow > a >>> single instance of DP controller to send multiple streams. > > >> This series has been validated on sa8775p ride platform using multiple > MST >> dongles and also daisy chain method on both DP0 and DP1 upto 1080P. > > With >> 4x4K monitors, due to lack of layer mixers that combination will > not > >> work but this can be supported as well after some rework on the DPU > side. >>>> In addition, SST was re-validated with all these changes to ensure > >> there > were no regressions. >> I have applied this patch series onto a near mainline 7.3 tree for the >> Xiaomi Pad 6s Pro ("Sheng"), with SM8550. But with these patches >> applied I don't have working audio, over USB-C to my (DisplayPort) >> monitor, anymore. If I disable MST support on the monitor audio works >> again. Debugging (using AI) reveals that the DP0 Jack is not reported as >> connected anymore when connected to the monitor, with these patches >> applied and MST enabled on the monitor. As shown, for example, by >> amixer: >> >> $ amixer -c 0 contents | grep -i -A8 -B3 -E 'hdmi|displayport|jack' >> numid=208,iface=CARD,name='DP0 Jack' >> ; type=BOOLEAN,access=r-------,values=1 >> : values=off >> >> With MST on the monitor disabled this outputs "values=on". The same is >> also reflected by "pactl list cards" and "pactl list sinks" where >> HDMI/DisplayPort is reported as "not available" with MST enabled (and >> "available" when disabling MST). >> >> (Again, suggested by AI) I also checked the ELD, which in both >> cases (MST on and off on the monitor) is identical, including audio >> information (like "speakers [0x1] FL/FR"). (Also, audio works both using >> an AMD and an Intel based laptop, in which case I can also choose >> whether to use "HDMI" or "HDMI 2" to switch audio output between two >> monitors, in daisy chain). >> >> So my foremost question is: should audio be supported in case of MST, >> after applying these patches? Or is this possibly out of scope? > > I'd say, it was out of scope for now. > >> For clarity I would also like to note that without these patches >> applied audio over DP does work as well, irrespective of MST being >> on or off on the monitor (obviously always running as SST because of >> missing kernel support). Which would make me believe that no audio >> support in the same setup might be considered a regression? > > Technically you are right, it is a regression in your case. > > Yongxing, how difficult would it be to support audio over the MST? > I don't think it should be too difficult. It would mainly involve programming some audio-related registers for each MST stream. But I haven't actually tried it yet. >> >> Note that I do understand that me running a forked kernel on a >> (by upstream) unsupported device might also lead to issues or require >> changes for the fork. And that if audio does work with MST then this is >> something the maintainers of the fork should, most likely, fix. But >> from the cover letter and commit messages it is unclear to me whether >> audio support should work and/or has been tested when MST is in use. >> >> Kind regards, >> Robert >> >