From: Paul Cercueil <paul@crapouillou.net>
To: "Noralf Trønnes" <noralf@tronnes.org>
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 22:42:29 +0200 [thread overview]
Message-ID: <T6SUAQ.4AZ5S5FWL6VZ@crapouillou.net> (raw)
In-Reply-To: <0f860795-218e-b9f0-0d1c-699024d3cc9a@tronnes.org>
Le dim. 24 mai 2020 à 22:14, Noralf Trønnes <noralf@tronnes.org> a
écrit :
>
>
> 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.
It wouldn't appear in devicetree. If the panel is connected over SPI,
then DBI is just the protocol it uses.
If probed as a SPI device driver, the panel's spi_driver would register
an instance of the DBI/SPI host driver, then register itself as a
dbi_driver. If probed from a DBI host it would just register itself as
a dbi_driver.
-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:[~2020-05-25 7:22 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
2020-05-24 20:42 ` Paul Cercueil [this message]
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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