From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5C29528B41E for ; Thu, 17 Jul 2025 10:30:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752748202; cv=none; b=psoNw95bIZjcBslb4sOhSJUug3TYxIXOmNwZIUISq2EHAu5uDsqpx2hJQ3rUZJaYNk5SiTPwPZbE8bI0tcsgoM8yGX/2jJTcOhNn1KJynQNrY9hO3W/e0Edm1g9TUq0T5HMXQOKusfRg773pvO7sOKczZm+gXsYuPVQEEUYGQPg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752748202; c=relaxed/simple; bh=vdLYDH/0FP+BqD0OZjHgZRlz3qLb2TjSX75DQnNBPOw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=dz5yarVebNs6CCT+f6qQ8N1T7/IFuvvIrj11eB5EIb3H8UbDVhVwePclG9Feuj1zFXAbnP5XUcWyLcTN4VWjNzRq1OHM2lSEFITjnzf0GsMovNRSA9mfnMgfYjrh4gKaK1m57d4MuXx3SrrxElBS5RVMk8pv2gBy1myksuxRMHc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=mIynV+0U; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="mIynV+0U" Received: from [192.168.88.20] (91-158-153-178.elisa-laajakaista.fi [91.158.153.178]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 5742DE92; Thu, 17 Jul 2025 12:29:22 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1752748164; bh=vdLYDH/0FP+BqD0OZjHgZRlz3qLb2TjSX75DQnNBPOw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=mIynV+0Up6dKjNsz70e+5XjvSmImQe7bp80kQCu/wpkU4H1DwJAXYdVyJspOGpcu2 hTeQkVmJeztY1KhicnOZvd6pMobTA6KuqpVV73MvEk9/8nTs9tiEtyeAdKItxTETca lCZl9oqPlBAdrksbOfMvLeCFcWnR7H0aKHr6fWRM= Message-ID: <5377d377-2822-4d35-981e-45e7352ade17@ideasonboard.com> Date: Thu, 17 Jul 2025 13:29:52 +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 v4 17/17] drm/bridge: cdns-dsi: Don't fail on MIPI_DSI_MODE_VIDEO_BURST To: Devarsh Thakkar Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-phy@lists.infradead.org, Francesco Dolcini , Aradhya Bhatia , Parth Pancholi , Jyri Sarha , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Vinod Koul , Kishon Vijay Abraham I , Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Jayesh Choudhary , Dmitry Baryshkov References: <20250618-cdns-dsi-impro-v4-0-862c841dbe02@ideasonboard.com> <20250618-cdns-dsi-impro-v4-17-862c841dbe02@ideasonboard.com> <8728de80-f154-46fa-a8a6-da40cb5fdc65@ti.com> Content-Language: en-US From: Tomi Valkeinen Autocrypt: addr=tomi.valkeinen@ideasonboard.com; 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charset=UTF-8 Content-Transfer-Encoding: 8bit Hi, On 17/07/2025 12:36, Devarsh Thakkar wrote: > Hi Tomi > > Thanks for the patch. > > On 18/06/25 15:29, Tomi Valkeinen wrote: >> While the cdns-dsi does not support DSI burst mode, the burst mode is >> essentially DSI event mode with more versatile clocking and timings. > I don't fully agree with this statement, DSI burst mode and DSI event > mode are two different things having separate requirements. DSI burst > mode maps to MIPI_DSI_MODE_VIDEO_BURST. I don't see a separate flag for > event mode but I guess, Well, what does DSI burst mode mean? Signal-wise it's the same as DSI event mode. "burst" just means that the DSI TX is allowed to send the data much faster than the pixel clock. But there's no strict requirement that it _must_ be faster. So, DSI burst mode is basically DSI event mode with more freedom on the timings. Thus, afaics, DSI TX in DSI event mode should always work if the DSI RX expects DSI burst mode. Tomi >> Thus cdns-dsi doesn't need to fail if the DSI peripheral driver requests >> MIPI_DSI_MODE_VIDEO_BURST. > > MIPI_DSI_MODE_VIDEO_BURST is currently not supported by the cadence DSI > host driver, so only if DSI peripheral driver is saying that burst mode > is the only one it supports in that case only we should fail. > >> >> In my particular use case, this allows the use of ti-sn65dsi83 driver. >> >> Tested-by: Parth Pancholi >> Tested-by: Jayesh Choudhary >> Signed-off-by: Tomi Valkeinen >> --- >>   drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c | 4 ---- >>   1 file changed, 4 deletions(-) >> >> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/ >> gpu/drm/bridge/cadence/cdns-dsi-core.c >> index 114d883c65dc..09b289f0fcbf 100644 >> --- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c >> +++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c >> @@ -1052,10 +1052,6 @@ static int cdns_dsi_attach(struct mipi_dsi_host >> *host, >>       if (output->dev) >>           return -EBUSY; >>   -    /* We do not support burst mode yet. */ >> -    if (dev->mode_flags & MIPI_DSI_MODE_VIDEO_BURST) >> -        return -ENOTSUPP; >> - > > Removing this check also gives a false impression that burst mode is > supported by the driver and can also lead to failures too in case device > is only supporting burst mode. > > I think it makes sense to fail only if burst mode is the only one being > supported by the device, something like below should work I believe, > > if (dev->mode_flags & MIPI_DSI_MODE_VIDEO_BURST == > MIPI_DSI_MODE_VIDEO_BURST) >         return -ENOTSUPP; > > Regards > Devarsh > >>       /* >>        * The host <-> device link might be described using an OF-graph >>        * representation, in this case we extract the device of_node from >>