linux-kernel - Re: [PATCH]"drm: change DRM_MIPI_DSI module type from "bool" to "tristate".

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Message-id: <34ef3414-952d-461f-bc3c-a47fadd1b69a@samsung.com>
Date:   Thu, 20 Oct 2016 15:20:56 +0200
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Emil Velikov <emil.l.velikov@...il.com>
Cc:     "Sun, Jing A" <jing.a.sun@...el.com>, Takashi Iwai <tiwai@...e.de>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "Vetter, Daniel" <daniel.vetter@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Thierry Reding <treding@...dia.com>
Subject: Re:
 [PATCH]"drm: change DRM_MIPI_DSI module type from "bool" to "tristate".

Hi Jani,

Forgive me late response.

On 12.10.2016 16:28, Jani Nikula wrote:
> On Wed, 12 Oct 2016, Emil Velikov <emil.l.velikov@...il.com> wrote:
>> On 11 October 2016 at 10:33, Jani Nikula <jani.nikula@...ux.intel.com> wrote:
>>> On Tue, 11 Oct 2016, "Sun, Jing A" <jing.a.sun@...el.com> wrote:
>>>> It's needed that DRM Driver module could be removed and reloaded after
>>>> kernel booting on the projects that I have been working on, and I hope
>>>> such module type change could be accepted. Looks like Iwai has similar
>>>> change request as well. Would you please review it and let us know if
>>>> any concerns?
>>> Looking at the Kconfig, selecting CONFIG_DRM_MIPI_DSI is against the
>>> recommendations of Documentation/kbuild/kconfig-language.txt:
>>>
>>>         select should be used with care. select will force
>>>         a symbol to a value without visiting the dependencies.
>>>         By abusing select you are able to select a symbol FOO even
>>>         if FOO depends on BAR that is not set.
>>>         In general use select only for non-visible symbols
>>>         (no prompts anywhere) and for symbols with no dependencies.
>>>         That will limit the usefulness but on the other hand avoid
>>>         the illegal configurations all over.
>>>
>>> Indeed, you may end up with CONFIG_DRM_MIPI_DSI=y and CONFIG_DRM=m,
>>> which violates DRM_MIPI_DSI dependency on CONFIG_DRM. This is broken and
>>> should be fixed. The suggested patch does *not* fix this issue.
>>>
>> Jani, git log suggests you as the unfortunate author of the select
>> DRM_MIPI_DSI/select DRM_PANEL hunks in i915 ;-)
> /o\
>
> As much as my present self would like to scold my past self for all his
> mistakes, I have to remind myself that it is the mistakes that have
> given me invaluable experience that my past self didn't have. I can only
> hope my future self will have time to fix even a fraction of the
> mistakes.
>
> Anyway, as Andrzej pointed out, all configs that select DRM_MIPI_DSI
> also depend on DRM, so this problem can't currently occur. Once dsi bus
> un-registration gets addressed, we can turn DRM_MIPI_DSI into a tristate
> config (i.e. a loadable module).

There is already patch adding bus unregistration [1]. It was published
together
with 'tristate' patch [2], both were created by Takashi few months ago.

[1]:
https://lists.freedesktop.org/archives/dri-devel/2016-August/114870.html
[2]:
https://lists.freedesktop.org/archives/dri-devel/2016-August/114497.html

Regards
Andrzej

>
> BR,
> Jani.
>