From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 8DDFCFA0C3D for ; Wed, 15 Apr 2026 07:14:05 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id B55E710E5CA; Wed, 15 Apr 2026 07:14:04 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=bootlin.com header.i=@bootlin.com header.b="1jt44X/V"; dkim-atps=neutral Received: from smtpout-03.galae.net (smtpout-03.galae.net [185.246.85.4]) by gabe.freedesktop.org (Postfix) with ESMTPS id 0514110E5CA for ; Wed, 15 Apr 2026 07:14:02 +0000 (UTC) Received: from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233]) by smtpout-03.galae.net (Postfix) with ESMTPS id 669FC4E429FB; Wed, 15 Apr 2026 07:14:01 +0000 (UTC) Received: from mail.galae.net (mail.galae.net [212.83.136.155]) by smtpout-01.galae.net (Postfix) with ESMTPS id 28D1860420; Wed, 15 Apr 2026 07:14:01 +0000 (UTC) Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id C5B6B10451BC6; Wed, 15 Apr 2026 09:13:53 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim; t=1776237240; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=iygYfs8OpmDj7EArekkpuMFiF4SNkAQXIDO0MbSPk1k=; b=1jt44X/VHX7vc5fMwQRP6HQk0nq4iNKzijy4m3ZrruuZ7Cshdkf3HdB8EgDePX3j9pJEum WGcJkENB7V333mLkx4o/nx7giqakav5UhfdrDCTTS4GC4k0Y7HkBHRIJsWvnZVyNUF0wtH 5NAv+Pq0CQZkc1QNhJc9cbvKN6hDD2/jl8WJMnuESumcp58+Pcr5QWrFfuRERqlk6zuMVF Yf2gMKUKPs1DQTdvXySbnoagMQXLPG2YErsOJuDU2to0O4OOyEuOWifoxJJe55FuI/v60c OtIVB4XmAUhDnU3DX8UUbQGcDh8BkEsuuhiNjZIqX+Csb36JI578kVRs8qEb2w== Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Wed, 15 Apr 2026 09:13:52 +0200 Message-Id: Subject: Re: [PATCH v3 1/1] drm: bridge: ti-sn65dsi83: Fix DSI mode flags for stable LVDS output Cc: , , , , , , , , , , , , , To: "Sudarshan Shetty" , , , From: "Luca Ceresoli" X-Mailer: aerc 0.20.1 References: <20260412053811.662461-1-tessolveupstream@gmail.com> <20260412053811.662461-2-tessolveupstream@gmail.com> In-Reply-To: <20260412053811.662461-2-tessolveupstream@gmail.com> X-Last-TLS-Session-Version: TLSv1.3 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hello Sudarshan, On Sun Apr 12, 2026 at 7:38 AM CEST, Sudarshan Shetty wrote: > The current DSI mode configuration enables VIDEO_BURST and disables > horizontal front porch (HFP) and back porch (HBP) transmission using > MIPI_DSI_MODE_VIDEO_NO_HFP and MIPI_DSI_MODE_VIDEO_NO_HBP. > > However, the SN65DSI83/84 bridge relies on receiving full horizontal > timing information over DSI in order to correctly reconstruct the LVDS > output timings. When HFP and HBP are not transmitted, the bridge cannot > recreate the required timing parameters, resulting in unstable or > missing display output on some panels. > > Additionally, while burst mode is supported by the hardware, its use > depends on continuous clock behavior from the DSI host. In practice, > burst mode may introduce instability depending on the host controller > implementation, as the DSI link may transition to low-power state > between bursts. > > In testing, removing burst mode and ensuring full horizontal timing > transmission results in stable LVDS output across affected panels. > > Update the DSI mode flags to: > - Drop MIPI_DSI_MODE_VIDEO_BURST > - Drop MIPI_DSI_MODE_VIDEO_NO_HFP > - Drop MIPI_DSI_MODE_VIDEO_NO_HBP > > This aligns with common system configurations where non-burst mode is > preferred and full timing information is transmitted over DSI. > > Signed-off-by: Sudarshan Shetty Thanks for having gone into the details and provide a good explanation for the removal of these three flags. It would be still great to have authoritative info from TI, possibly as an update to the documentation. I managed to test on a board with i.MX93, a TI SN65DSI84 and a 1920x1080p60 panel, and: - no image shown with the current mainline driver - it works by removing only MIPI_DSI_MODE_VIDEO_BURST (my current setup) - it works with this patch applied Tested-by: Luca Ceresoli # imx93 1920x1080p60 Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com