Re: [PATCH] drm: rcar-du: Put reference to VSP device

[Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>]

Hi Laurent,

On 16/09/2020 00:38, Laurent Pinchart wrote:
> The reference to the VSP device acquired with of_find_device_by_node()
> in rcar_du_vsp_init() is never released. Fix it with a drmm action,
> which gets run both in the probe error path and in the remove path.
> 
> Fixes: 6d62ef3ac30b ("drm: rcar-du: Expose the VSP1 compositor through KMS planes")
> Reported-by: Yu Kuai <yukuai3@huawei.com>
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

Looks nice and clean!

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

> ---
>  drivers/gpu/drm/rcar-du/rcar_du_vsp.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> index f1a81c9b184d..fa09b3ae8b9d 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> @@ -13,6 +13,7 @@
>  #include <drm/drm_fourcc.h>
>  #include <drm/drm_gem_cma_helper.h>
>  #include <drm/drm_gem_framebuffer_helper.h>
> +#include <drm/drm_managed.h>
>  #include <drm/drm_plane_helper.h>
>  #include <drm/drm_vblank.h>
>  
> @@ -341,6 +342,13 @@ static const struct drm_plane_funcs rcar_du_vsp_plane_funcs = {
>  	.atomic_destroy_state = rcar_du_vsp_plane_atomic_destroy_state,
>  };
>  
> +static void rcar_du_vsp_cleanup(struct drm_device *dev, void *res)
> +{
> +	struct rcar_du_vsp *vsp = res;
> +
> +	put_device(vsp->vsp);

Ugh the asymmetry of the put_device is a bit annoying, because it's not
initially clear that the of_find_device_by_node() call 'gets' a reference.

(Or at least not until you find:
  https://lore.kernel.org/patchwork/patch/731284/)

It is stated in the commit message though so that's fine, and although I
thought perhaps a comment here might be useful to declare that it
releases the reference taken by of_find_device_by_node(), I'm not sure
it even adds that much value ... so either way.


> +}
> +
>  int rcar_du_vsp_init(struct rcar_du_vsp *vsp, struct device_node *np,
>  		     unsigned int crtcs)
>  {
> @@ -357,6 +365,10 @@ int rcar_du_vsp_init(struct rcar_du_vsp *vsp, struct device_node *np,
>  
>  	vsp->vsp = &pdev->dev;
>  
> +	ret = drmm_add_action(rcdu->ddev, rcar_du_vsp_cleanup, vsp);
> +	if (ret < 0)
> +		return ret;
> +
>  	ret = vsp1_du_init(vsp->vsp);
>  	if (ret < 0)
>  		return ret;
> 

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