From: "Noralf Trønnes" <noralf@tronnes.org>
To: Paul Cercueil <paul@crapouillou.net>
Cc: Sam Ravnborg <sam@ravnborg.org>,
dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: MIPI DSI, DBI, and tinydrm drivers
Date: Sun, 24 May 2020 22:14:10 +0200 [thread overview]
Message-ID: <0f860795-218e-b9f0-0d1c-699024d3cc9a@tronnes.org> (raw)
In-Reply-To: <3YPUAQ.ALFWN74JD6DR1@crapouillou.net>
Den 24.05.2020 21.54, skrev Paul Cercueil:
> Hi Noralf,
>
> Le dim. 24 mai 2020 à 19:46, Noralf Trønnes <noralf@tronnes.org> a écrit :
>>
>>
>> Den 24.05.2020 18.13, skrev Paul Cercueil:
>>> Hi list,
>>>
>>> I'd like to open a discussion about the current support of MIPI DSI and
>>> DBI panels.
>>>
>>> Both are standards from the MIPI alliance, both are communication
>>> protocols between a LCD controller and a LCD panel, they generally both
>>> use the same commands (DCS), the main difference is that DSI is serial
>>> and DBI is generally parallel.
>>>
>>> In the kernel right now, DSI is pretty well implemented. All the
>>> infrastucture to register a DSI host, DSI device etc. is there. DSI
>>> panels are implemented as regular drm_panel instances, and their
>>> drivers
>>> go through the DSI API to communicate with the panel, which makes them
>>> independent of the DSI host driver.
>>>
>>> DBI, on the other hand, does not have any of this. All (?) DBI panels
>>> are implemented as tinydrm drivers, which make them impossible to use
>>> with regular DRM drivers. Writing a standard drm_panel driver is
>>> impossible, as there is no concept of host and device. All these
>>> tinydrm
>>> drivers register their own DBI host as they all do DBI over SPI.
>>>
>>> I think this needs a good cleanup. Given that DSI and DBI are so
>>> similar, it would probably make sense to fuse DBI support into the
>>> current DSI code, as trying to update DBI would result in a lot of code
>>> being duplicated. With the proper host/device registration mechanism
>>> from DSI code, it would be possible to turn most of the tinydrm drivers
>>> into regular drm_panel drivers.
>>>
>>> The problem then is that these should still be available as tinydrm
>>> drivers. If the DSI/DBI panels can somehow register a .update_fb()
>>> callback, it would make it possible to have a panel-agnostic tinydrm
>>> driver, which would then probably open a lot of doors, and help a
>>> lot to
>>> clean the mess.
>>>
>>> I think I can help with that, I just need some guidance - I am fishing
>>> in exotic seas here.
>>>
>>> Thoughts, comments, are very welcome.
>>
>> I did look at this a few months back:
>>
>> drm/mipi-dbi: Support panel drivers
>> https://lists.freedesktop.org/archives/dri-devel/2019-August/228966.html
>>
>> The problem with DBI is that it has reused other busses which means we
>> don't have DBI drivers, we have SPI drivers instead (6800/8080 is not
>> avail. as busses in Linux yet). DSI and DPI on the other hand has
>> dedicated hw controller drivers not shared with other subsystems.
>
> I don't think that should be much of a problem. You could have a DBI/SPI
> bridge, that wraps a SPI device into a DBI host, for instance. The panel
> drivers would just use the DBI API without having to know what's done
> behind the scene.
This will be a bridge implemented in software, are we allowed to have
software devices in the Device Tree? I though it was just allowed to
describe hardware.
Noralf.
>
> Cheers,
> -Paul
>
>> My initial tinydrm work used drm_panel, but I was not allowed to use it
>> (at least not the way I had done it).
>>
>> Noralf.
>>
>>>
>>> Cheers,
>>> -Paul
>>>
>>>
>
>
>
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next prev parent reply other threads:[~2020-05-24 20:14 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-24 16:13 MIPI DSI, DBI, and tinydrm drivers Paul Cercueil
2020-05-24 17:46 ` Noralf Trønnes
2020-05-24 18:35 ` Daniel Vetter
2020-05-24 19:50 ` Paul Cercueil
2020-05-25 14:58 ` Neil Armstrong
2020-05-27 12:10 ` Paul Cercueil
2020-05-25 10:08 ` Noralf Trønnes
2020-05-28 15:27 ` Emil Velikov
2020-06-03 12:15 ` Noralf Trønnes
2020-06-03 20:25 ` Emil Velikov
2020-06-05 12:58 ` Noralf Trønnes
2020-05-24 19:54 ` Paul Cercueil
2020-05-24 20:14 ` Noralf Trønnes [this message]
2020-05-24 20:42 ` Paul Cercueil
2020-05-24 21:24 ` Noralf Trønnes
2020-05-24 21:33 ` Paul Cercueil
2020-05-25 0:46 ` Noralf Trønnes
2020-05-25 2:05 ` Paul Cercueil
2020-05-25 13:23 ` Noralf Trønnes
2020-05-24 20:06 ` Sam Ravnborg
2020-05-25 1:46 ` Paul Cercueil
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