Re: [PATCH RFC v2 13/24] drm/mipi-dsi: turn DRM_MIPI_DSI into a tristate

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] module: drm_mipi_dsi cannot be unloaded and leaks bus registration
- [Low] kbuild: Linker error due to IS_ENABLED(CONFIG_DRM_MIPI_DSI) when built as module
--

commit 33f0d16c5b1d57480468538aae543a48ddad02aa
Author: Luca Ceresoli <luca.ceresoli@bootlin.com>

drm/mipi-dsi: turn DRM_MIPI_DSI into a tristate

DRM_MIPI_DSI is currently a bool, but there's no reason to not be allowed
to build it as a loadable module.

> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 65d46dfa72661..9bdd9110e754b 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -39,7 +39,7 @@ config DRM_MIPI_DBI
>  	select DRM_KMS_HELPER
>  
>  config DRM_MIPI_DSI
> -	bool
> +	tristate

[Severity: Low]
Will this cause a linker error when CONFIG_DRM=y and CONFIG_DRM_MIPI_DSI=m?

Since IS_ENABLED(CONFIG_DRM_MIPI_DSI) is true for both 'y' and 'm',
built-in code will attempt to call exported symbols from the now-loadable
drm_mipi_dsi module, leading to undefined references during the build.
For example, in drivers/gpu/drm/drm_of.c:

drm_of_get_dsi_bus() {
    ...
    #if IS_ENABLED(CONFIG_DRM_MIPI_DSI)
    ...
    dsi_host = of_find_mipi_dsi_host_by_node(dsi_host_node);
    ...
}

[Severity: Medium]
Does the drm_mipi_dsi module need a module_exit() cleanup function now that
it can be built as a loadable module?

Currently, mipi_dsi_bus_init() in drivers/gpu/drm/drm_mipi_dsi.c registers
the bus during initialization, but there is no corresponding module_exit()
to unregister it:

static int __init mipi_dsi_bus_init(void)
{
	return bus_register(&mipi_dsi_bus_type);
}
postcore_initcall(mipi_dsi_bus_init);

If the module is forcefully unloaded, it will leave a dangling
mipi_dsi_bus_type registration in the driver core.

[Severity: Low]
This is a pre-existing issue, but does changing this to a tristate still
leave an unmet dependency warning when selected by boolean configs?

For example, config DRM_MSM_DSI in drivers/gpu/drm/msm/Kconfig is a bool
that selects DRM_MIPI_DSI:

config DRM_MSM_DSI
	bool "Enable DSI support in MSM DRM driver"
	depends on DRM_MSM
	depends on DRM_MSM_KMS
	select DRM_PANEL
	select DRM_MIPI_DSI

If CONFIG_DRM=m and CONFIG_DRM_MSM_DSI=y, this forces CONFIG_DRM_MIPI_DSI
to 'y', violating its 'depends on DRM' restriction.

>  	depends on DRM
>  
>  config DRM_KMS_HELPER

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261001-drm-bridge-hotplug-v2-0-8e34986dcb68@bootlin.com?part=13