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

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Date:   Sat, 16 Jun 2018 01:32:44 +0200
From:   Marek Vasut <marek.vasut@...il.com>
To:     Leonard Crestez <leonard.crestez@....com>,
        "festevam@...il.com" <festevam@...il.com>,
        "stefan@...er.ch" <stefan@...er.ch>,
        "marex@...x.de" <marex@...x.de>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>
Cc:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        "marcofrk@...il.com" <marcofrk@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        dl-linux-imx <linux-imx@....com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "l.stach@...gutronix.de" <l.stach@...gutronix.de>
Subject: Re: [PATCH 1/3] drm: mxsfb: Change driver.name to mxsfb-drm

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.

-- 
Best regards,
Marek Vasut