Subject: Re:
 [PATCH]"drm: change DRM_MIPI_DSI module type from "bool" to "tristate".
To: Jani Nikula <jani.nikula@linux.intel.com>,
        "Sun, Jing A" <jing.a.sun@intel.com>, Takashi Iwai <tiwai@suse.de>
Cc: "airlied@linux.ie" <airlied@linux.ie>,
        "Vetter, Daniel" <daniel.vetter@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        Thierry Reding <treding@nvidia.com>,
        Emil Velikov <emil.l.velikov@gmail.com>
From: Andrzej Hajda <a.hajda@samsung.com>
Message-id: <bc014930-9957-8ca4-435d-737b0fdb3920@samsung.com>
Date: Tue, 11 Oct 2016 11:53:09 +0200
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On 11.10.2016 11:33, Jani Nikula wrote:
> On Tue, 11 Oct 2016, "Sun, Jing A" <jing.a.sun@intel.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.

All existing drivers which selects DRM_MIPI_DSI also depends on DRM.
So the dependency is always true. I am not sure if it could not change in
the future, but in such case mipi_dsi bus should be completely detached from
DRM framework, I hope we have not such case yet :)

>
> 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.

At the moment it should not be possible.

Regards
Andrzej