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

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Message-ID: <fd22085f646d97f66cff5b7f22785500@agner.ch>
Date:   Tue, 10 Jul 2018 11:06:36 +0200
From:   Stefan Agner <stefan@...er.ch>
To:     Marek Vasut <marek.vasut@...il.com>
Cc:     Leonard Crestez <leonard.crestez@....com>, festevam@...il.com,
        marex@...x.de, 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,
        Fabio Estevam <fabio.estevam@....com>,
        linux-arm-kernel@...ts.infradead.org, l.stach@...gutronix.de
Subject: Re: [PATCH 1/3] drm: mxsfb: Change driver.name to mxsfb-drm

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
- 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.

--
Stefan