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Wed, 20 May 2026 02:04:58 -0700 (PDT) Message-ID: <1716be56-ac43-440b-a5df-58cbf571ba95@gmail.com> Date: Wed, 20 May 2026 14:34:49 +0530 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 v3 1/1] drm: bridge: ti-sn65dsi83: Fix DSI mode flags for stable LVDS output To: Luca Ceresoli , andrzej.hajda@intel.com, neil.armstrong@linaro.org, rfoss@kernel.org Cc: Laurent.pinchart@ideasonboard.com, jonas@kwiboo.se, jernej.skrabec@gmail.com, maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com, simona@ffwll.ch, marex@denx.de, valentin@compulab.co.il, philippe.schenker@toradex.com, alexander.stein@ew.tq-group.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20260412053811.662461-1-tessolveupstream@gmail.com> <20260412053811.662461-2-tessolveupstream@gmail.com> <7056b23b-ed81-4d79-b782-5cfcb0102ef7@gmail.com> <60a24977-b181-40e4-bcf6-38b65af293e2@gmail.com> Content-Language: en-US From: tessolveupstream@gmail.com In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 19-05-2026 17:13, Luca Ceresoli wrote: > Hello, > > On Tue May 19, 2026 at 10:48 AM CEST, tessolveupstream wrote: >> >> >> On 24-04-2026 13:55, Luca Ceresoli wrote: >>> Hello, >>> >>> On Thu Apr 23, 2026 at 11:16 AM CEST, tessolveupstream wrote: >>> >>>>> I had reached out to TI for clarification and any related documentation >>>>> updates, but I have not received any response so far.Given this, it is >>>>> uncertain whether we will be able to obtain further details or official >>>>> confirmation from TI in the near term. >>>>> >>>>> I would appreciate your guidance on how you would prefer us to proceed >>>>> from here. >>>> >>>> I followed up with TI, and they pointed us to the relevant sections in the >>>> SN65DSI83/84/86 datasheets covering DSI video transmission specifications. >>> >>> Thanks for keeping on! I'm also trying to get info from TI, I'm keeping you >>> up to date if that will happen. >>> >>>>> https://www.ti.com/lit/ds/symlink/sn65dsi84.pdf?ts=1776924088430&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FSN65DSI84 >>>> >>>> As per datasheet Section 7.4.7, the device operates in DSI video mode with >>>> fixed horizontal timing, where HBP, and HFP are explicitly defined and expected >>>> to be present as part of the video line structure. The timing description in >>>> this section assumes standard non‑burst video transmission with all horizontal >>>> blanking intervals accounted for. >>>> >>>> The datasheet does not document support for DSI video burst mode, >>> >>> This sentence seems incorrect. Section 7.4.7 starts with this sentence: >>> "The SN65DSI84 supports burst video mode and non-burst video mode ...". >>> >>> Even though asa matter of fact it looks like many users have issues that >>> get solved by disabling burst mode. >>> >>>> nor does it >>>> mention support for omitting horizontal front or back porch intervals. In >>>> particular, there is no indication that the device can operate with collapsed >>>> or suppressed horizontal blanking, as enabled by MIPI_DSI_MODE_VIDEO_BURST, >>>> MIPI_DSI_MODE_VIDEO_NO_HFP, or MIPI_DSI_MODE_VIDEO_NO_HBP. >>> >>> This is correct. >>> >>> We can still try to get TI feedback, but it that won't happen in, say, a >>> few weeks then I think we should apply this patch. >>> >> >> We have not received any further updates from TI regarding this issue, and >> at this point, we are not sure if we will get additional feedback from them. >> As you had mentioned earlier that the patch could be considered after >> waiting for some time, could you please let us know how we can proceed >> further from here? > > I am getting some feedback from TI, but it is taking some time. > > For the time being I think it is clear that HBP and HFP are required, and > so removing the MIPI_DSI_MODE_VIDEO_NO_HFP and MIPI_DSI_MODE_VIDEO_NO_HBP > in your patch seems to be fully correct, even though this had no effect on > the panel I tested. > > I'm still trying to get some better info to ensure that switching from > burst mode to non-burst mode is not expected to have side effects. > > For thi reason, I think it would be great if you could send a new version > with two separate patches: the first one enabling HFP and HBP and which can > be applied right away, the second to disable burst mode for which I'd wait > a bit longer for TI feedback. You can keep the Tested-by lines. > Thanks for the clarification. I just wanted to confirm my understanding regarding the patch split you suggested. >From your comments, my understanding is that the first patch would only enable HFP and HBP by removing MIPI_DSI_MODE_VIDEO_NO_HFP and MIPI_DSI_MODE_VIDEO_NO_HBP, while keeping burst mode enabled, so the mode flags would become: dsi->mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_VIDEO_BURST | MIPI_DSI_MODE_VIDEO_NO_HSA | MIPI_DSI_MODE_NO_EOT_PACKET; Then, the second patch would only disable burst mode, resulting in: dsi->mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_VIDEO_NO_HSA | MIPI_DSI_MODE_NO_EOT_PACKET; Could you please confirm whether my understanding is correct? Also, from our testing, when using: dsi->mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_VIDEO_BURST | MIPI_DSI_MODE_VIDEO_NO_HSA | MIPI_DSI_MODE_NO_EOT_PACKET; we are not able to get display output. I just wanted to mention this observation in case it is relevant to the patch split discussion. Additionally, regarding the Tested-by tags you mentioned earlier, should I carry them forward to both patches, or would you prefer them only on the applicable patch? > I understand this is painful and taking time, but it's important to ensure > as much as possible that the change won't introduce regressions on existing > hardware. > > Luca > > -- > Luca Ceresoli, Bootlin > Embedded Linux and Kernel engineering > https://bootlin.com