Re: [PATCH v12 00/18] drm: Add Samsung MIPI DSIM bridge

From: Frieder Schrempf <frieder.schrempf@kontron.de>
To: Rasmus Villemoes <rasmus.villemoes@prevas.dk>,
	Marek Vasut <marex@denx.de>,
	Jagan Teki <jagan@amarulasolutions.com>
Cc: Laurent.pinchart@ideasonboard.com, aford173@gmail.com,
	andrzej.hajda@intel.com, dri-devel@lists.freedesktop.org,
	inki.dae@samsung.com, kyungmin.park@samsung.com,
	linux-amarula@amarulasolutions.com,
	linux-arm-kernel@lists.infradead.org, linux-imx@nxp.com,
	linux-samsung-soc@vger.kernel.org, m.szyprowski@samsung.com,
	matteo.lisi@engicam.com, sw0312.kim@samsung.com,
	tharvey@gateworks.com
Subject: Re: [PATCH v12 00/18] drm: Add Samsung MIPI DSIM bridge
Date: Wed, 22 Feb 2023 11:05:09 +0100	[thread overview]
Message-ID: <657fa528-ca01-0c6a-2c2b-bb7f4a95096d@kontron.de> (raw)
In-Reply-To: <b246aae9-b719-02f9-dd0f-305b74611fab@prevas.dk>

On 17.02.23 19:22, Rasmus Villemoes wrote:
> On 07/02/2023 10.09, Rasmus Villemoes wrote:
> 
>> I managed to get the whole chain lcdif -> mipi -> bridge -> dp-connector
>> to probe with these settings
>>
> [...]
>> Now hotplug-detect doesn't work with the current sn65dsi86 driver, but
>> that's a separate issue; when I boot with a monitor attached, its edid
>> is correctly read out. But I still don't get any output, and the monitor
>> says "no signal" - my naive attempt (which has worked fine in other
>> cases) was to just dd /dev/urandom to /dev/fb0, so I'm clearly missing
>> some important step.
> 
> No idea if it's important, but in the NXP kernel, there's a
> 
> 	display-subsystem {
> 		compatible = "fsl,imx-display-subsystem";
> 		ports = <&lcdif1_disp>,
> 			<&lcdif2_disp>,
> 			<&lcdif3_disp>;
> 	};
> 
> node in imx8mp.dtsi, and when commenting out that node, the graphics
> ceases to work, even if all the devices in the lcdif->mipi->bridge chain
> actually probes. However, adding a corresponding node in mainline, which
> does have a driver for that "fsl,imx-display-subsystem", makes no
> difference; with or without that, I do get a /dev/fb0 device and the
> whole chain probes, but again the monitor says no signal.

The NXP kernel is completely different. AFAIK it uses the component
helpers to bundle all subdrivers from a central driver
(display-subsystem). This is not how the mainline approach using the
bridge driver interface works. So you can't compare them.

Did you look at this extensive thread with findings from Adam?

https://lore.kernel.org/lkml/CAHCN7xJ=N1vWVTBjArskJ59fyaLzmAGWfc0E=_iGizrDNR_Udw@mail.gmail.com/

It is related to HDMI, but I guess a lot of things are valid for DP, too.

Anyway, we need to get this series merged. Otherwise we can't work on
fixing all the other issues on top.

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