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

From: Andrzej Hajda
Date: Tue Oct 11 2016 - 05:56:18 EST

On 11.10.2016 11:33, Jani Nikula wrote:
> On Tue, 11 Oct 2016, "Sun, Jing A" <jing.a.sun@xxxxxxxxx> 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.