linux-kernel - Re: [PATCH 1/3] drm: mxsfb: Change driver.name to mxsfb-drm

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Message-ID: <0b5e15ff6aa7dd7dcb96bd9bdcc81f4d@agner.ch>
Date:   Thu, 12 Jul 2018 14:15:57 +0200
From:   Stefan Agner <stefan@...er.ch>
To:     Marek Vasut <marex@...x.de>, Fabio Estevam <fabio.estevam@....com>,
        gary.bisson@...ndarydevices.com, LW@...O-electronics.de,
        sebastien.szymanski@...adeus.com, jagan@...rulasolutions.com
Cc:     Marek Vasut <marek.vasut@...il.com>,
        Leonard Crestez <leonard.crestez@....com>, festevam@...il.com,
        shawnguo@...nel.org, devicetree@...r.kernel.org,
        linux-fbdev@...r.kernel.org, marcofrk@...il.com,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        dl-linux-imx <linux-imx@....com>, kernel@...gutronix.de,
        linux-arm-kernel@...ts.infradead.org, l.stach@...gutronix.de
Subject: Re: [PATCH 1/3] drm: mxsfb: Change driver.name to mxsfb-drm

[adding Authors of the problematic device trees]

On 10.07.2018 11:11, Marek Vasut wrote:
> On 07/10/2018 11:06 AM, Stefan Agner wrote:
>> On 16.06.2018 01:32, Marek Vasut wrote:
>>> On 06/16/2018 12:42 AM, Leonard Crestez wrote:
>>>> On Fri, 2018-06-15 at 23:36 +0200, Marek Vasut wrote:
>>>>> On 06/15/2018 10:58 PM, Leonard Crestez wrote:
>>>>>> On Fri, 2018-06-15 at 16:47 -0300, Fabio Estevam wrote:
>>>>>>> On Fri, Jun 15, 2018 at 4:43 PM, Leonard Crestez
>>>>>>> <leonard.crestez@....com> wrote:
>>>>
>>>>>>>> The FBDEV driver uses the same name and both can't be registered at the
>>>>>>>> same time. Fix this by renaming the drm driver to mxsfb-drm
>>>>>>>
>>>>>>> Stefan sent the same patch a few days ago:
>>>>>>
>>>>>> In that thread there is a proposal for removing the old fbdev/mxsfb
>>>>>> driver entirely.
>>>>>>
>>>>>> That would break old DTBs, isn't this generally considered bad? Also,
>>>>>> are we sure the removal of fbdev/mxsfb wouldn't lose any features?
>>>>>>
>>>>>> What my series does is make both drivers work with the same kernel
>>>>>> image and turns the choice into a board-level dtb decision. Supporting
>>>>>> everything at once seems desirable to me and it allows for a very
>>>>>> smooth upgrade path.
>>>>>
>>>>> Having two drivers in the kernel with different set of bugs is always bad.
>>>>>
>>>>>> The old driver could be removed later, after all users are converted.
>>>>>
>>>>> Both drivers were in for long enough already. And let's be realistic,
>>>>> how many MX23/MX28 users of old DTs with new kernels are there who
>>>>> cannot update the DT as well ?
>>>>
>>>> Grepping for "display =" in arch/arm/boot/dts/imx* I see that old
>>>> bindings are also used by 3rd-party boards for imx6/7:
>>>>  * imx6sx-nitrogen6sx
>>>>  * imx6ul-geam
>>>>  * imx6ul-isiot
>>>>  * imx6ul-opos6uldev
>>>>  * imx6ul-pico-hobbit
>>>>  * imx6ul-tx6ul
>>>>  * imx7d-nitrogen7
>>>
>>> Er, yes, a handful of boards which could be updated :)
>>>
>>>> Converting everything might be quite a bit of work, and explicitly
>>>> supporting old bindings is also work.
>>>
>>> Does adding support for old bindings justify the effort invested ? I
>>> doubt so, it only adds more code to maintain.
>>>
>>>> It is very confusing that there is a whole set of displays for imx6/7
>>>> which are supported by upstream but only with a non-default config.
>>>> While it is extremely common in the embedded field to have custom
>>>> configs the default one in the kernel should try to "just work".
>>>>
>>>> Couldn't this patch series be considered a bugfix? It was also
>>>> surprisingly small.
>>>
>>> I think it's just a workaround which allows you to postpone the real
>>> fix, and I don't like that.
>>
>> This is one of the situation where states quo is kinda the worst
>> situation.
>>
>> Currently imx_v6_v7_defconfig and mxs_defconfig actually still uses
>> CONFIG_FB_MXS.
>>
>> I understand that you'd rather prefer to move forward. I suggest we do
>> it in steps.
>>
>> In 4.19:
>>
>> - Change DRM driver.name to mxsfb-drm so we avoid conflicts for now
> 
> But this will break mesa if it depends on mxsfb name for ie. etnaviv
> binding.
> 
>> - Remove CONFIG_FB_MXS from imx_v6_v7_defconfig/mxs_defconfig now, and
>> only enable CONFIG_DRM_MXSFB=y
>> - Add (deprecated) to CONFIG_FB_MXS
>>
>> In 4.19/4.20:
>> - Fix the above device trees
>>
>> In 4.20/4.21:
>> - Remove FB_MXS
>>
>> Does that sound reasonable? If yes, I can send the patch set to do step
>> 1.
> 
> Can you fix the DTs for 4.19 too ?

Unfortunately updating the device trees turned out to be a non trivial
task especially as an outsider. The display needs to be supported in
drivers/gpu/drm/panel/panel-simple.c. Some displays might be already in
place, but if not, the display need to be added. Since for panel
bindings vendor and product information are needed, it is not possible
as an outsiders to make the conversion.

Jagan, Sebastien, Fabio, Lothar and Gary, could you maybe update the
respective device trees?

A conversion to the new bindings similar to commit a027d49fc193 ("ARM:
dts: imx7-colibri: use OF graph to describe the display") is what we are
looking for.

This will make sure that the boards keep working using the new MXSFB DRM
driver.

--
Stefan