Re: [PATCH 1/9] media: rzg2l-cru: Add device_link from CRU to CSI-2

[Tommaso Merciai]

Hi Jacopo,

On Mon, Jul 27, 2026 at 11:50:32AM +0200, Jacopo Mondi wrote:
> Hi Tommaso
>  one more thing
> 
> On Tue, Jun 16, 2026 at 07:05:31PM +0200, Tommaso Merciai wrote:
> > The CRU device depends on CSI-2 to operate. Without an explicit
> > device_link the PM core has no knowledge of this dependency and may
> > suspend CSI-2 while CRU is still active, or resume CRU before CSI-2
> > is ready.
> >
> > Add a DL_FLAG_STATELESS device_link from the CRU to CSI-2 when the
> > CSI-2 subdev binds. This instructs the PM core to suspend CRU before
> > CSI-2 and to resume CSI-2 before CRU. The link is deleted on unbind.
> >
> > Signed-off-by: Tommaso Merciai <tommaso.merciai.xr@xxxxxxxxxxxxxx>
> > ---
> >  drivers/media/platform/renesas/rzg2l-cru/rzg2l-core.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/media/platform/renesas/rzg2l-cru/rzg2l-core.c b/drivers/media/platform/renesas/rzg2l-cru/rzg2l-core.c
> > index 3c5fbd857371..1b12d91eaec9 100644
> > --- a/drivers/media/platform/renesas/rzg2l-cru/rzg2l-core.c
> > +++ b/drivers/media/platform/renesas/rzg2l-cru/rzg2l-core.c
> > @@ -101,6 +101,7 @@ static void rzg2l_cru_group_notify_unbind(struct v4l2_async_notifier *notifier,
> >  	mutex_lock(&cru->mdev_lock);
> 
> What is the mutex protecting here ?
> 
> (yes, unrelated to this patch, I know, just wondering if you should
> take the occasion to remove the guards from bind/unbind)


Good catch, I agree it looks redundant.

Looks like v4l2_async_nf_register() -> __v4l2_async_nf_register() already
takes mutex_lock(&list_lock) around the calls to .bound()/.complete(), and
v4l2_async_nf_unregister() does the same around .unbind(). So .bound(),
.unbind() and .complete() can never run concurrently with each other.

I think you are correct, we can drop the mdev_lock calls in bound()/unbind().


Kind Regards,
Tommaso

> 
> >
> >  	if (cru->csi.asd == asd) {
> > +		device_link_remove(cru->dev, subdev->dev);
> >  		cru->csi.subdev = NULL;
> >  		dev_dbg(cru->dev, "Unbind CSI-2 %s\n", subdev->name);
> >  	}
> > @@ -118,6 +119,12 @@ static int rzg2l_cru_group_notify_bound(struct v4l2_async_notifier *notifier,
> >
> >  	if (cru->csi.asd == asd) {
> >  		cru->csi.subdev = subdev;
> > +		if (!device_link_add(cru->dev, subdev->dev, DL_FLAG_STATELESS)) {
> > +			dev_err(cru->dev, "Failed to create device link to CSI-2 %s\n",
> > +				subdev->name);
> > +			mutex_unlock(&cru->mdev_lock);
> > +			return -EINVAL;
> > +		}
> >  		dev_dbg(cru->dev, "Bound CSI-2 %s\n", subdev->name);
> >  	}
> >
> > --
> > 2.54.0
> >