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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Kieran,

On Wed, Sep 16, 2020 at 11:26:36AM +0100, Kieran Bingham wrote:
> 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.

I think that the fact that drmm_add_action() is called right after
of_find_device_by_node() makes this explicit enough.

> > +}
> > +
> >  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;
> > 
> 

-- 
Regards,

Laurent Pinchart