[PATCH] drm/mxsfb: Disable overlay plane in mxsfb_plane_overlay_atomic_disable()

[Sam Ravnborg]

Hi Liu Ying.

On Mon, Jun 12, 2023 at 03:55:30PM +0800, Liu Ying wrote:
> When disabling overlay plane in mxsfb_plane_overlay_atomic_update(),
> overlay plane's framebuffer pointer is NULL.  So, dereferencing it would
> cause a kernel Oops(NULL pointer dereferencing).  Fix the issue by
> disabling overlay plane in mxsfb_plane_overlay_atomic_disable() instead.

Reading the above I had expected that some code was dropped from
mxsfb_plane_overlay_atomic_update().
I do not know the driver code, but was confused so decided to give
feedback.

	Sam

> 
> Fixes: cb285a5348e7 ("drm: mxsfb: Replace mxsfb_get_fb_paddr() with drm_fb_cma_get_gem_addr()")
> Signed-off-by: Liu Ying <victor.liu at nxp.com>
> ---
>  drivers/gpu/drm/mxsfb/mxsfb_kms.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> index 3bcc9c0f2019..7ed2516b6de0 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> @@ -611,6 +611,14 @@ static void mxsfb_plane_overlay_atomic_update(struct drm_plane *plane,
>  	writel(ctrl, mxsfb->base + LCDC_AS_CTRL);
>  }
>  
> +static void mxsfb_plane_overlay_atomic_disable(struct drm_plane *plane,
> +					       struct drm_atomic_state *state)
> +{
> +	struct mxsfb_drm_private *mxsfb = to_mxsfb_drm_private(plane->dev);
> +
> +	writel(0, mxsfb->base + LCDC_AS_CTRL);
> +}
> +
>  static bool mxsfb_format_mod_supported(struct drm_plane *plane,
>  				       uint32_t format,
>  				       uint64_t modifier)
> @@ -626,6 +634,7 @@ static const struct drm_plane_helper_funcs mxsfb_plane_primary_helper_funcs = {
>  static const struct drm_plane_helper_funcs mxsfb_plane_overlay_helper_funcs = {
>  	.atomic_check = mxsfb_plane_atomic_check,
>  	.atomic_update = mxsfb_plane_overlay_atomic_update,
> +	.atomic_disable = mxsfb_plane_overlay_atomic_disable,
>  };
>  
>  static const struct drm_plane_funcs mxsfb_plane_funcs = {
> -- 
> 2.37.1