Hi Laurent,
On 2021-07-19 16:15:45 +0300, Laurent Pinchart wrote:
> Hi Niklas,
>
> On Mon, Jul 19, 2021 at 02:26:36PM +0200, Niklas Söderlund wrote:
> > On 2021-07-19 14:10:39 +0200, Jacopo Mondi wrote:
> > > On Thu, Jul 08, 2021 at 11:55:50AM +0200, Niklas Söderlund wrote:
> > > > There is no need to protect 'cfg_fmt' in get_fmt() and set_fmt() as the
> > > > core protects these callbacks. As this is the only usage of the mutex it
> > > > can be removed.
> > >
> > > You know, I tried chasing where the vdev->lock used to protect the
> > > subdev's ioctl is set for mex9286 and I wasn't able to find it.
> > >
> > > Please validate my understanding:
> > >
> > > - The lock used by the core to protect the set/get format subdev ioctl
> > > is the one in subdev_do_ioctl_lock()
> > >
> > > static long subdev_do_ioctl_lock(struct file *file, unsigned int cmd, void *arg)
> > > {
> > > struct video_device *vdev = video_devdata(file);
> > > struct mutex *lock = vdev->lock;
>
> Let's also note that subdev operations can also be called directly
> within the kernel, in video node-centric setups for instance. There are
> little changes the max9286 driver would be used in such a setup, but the
> .get_fmt() operation can be called during pipeline validation too.
> That's why subdev drivers are supposed to use locks internally.
This is a good point which disregarding of the ioctl lock issue pointed
out by Jacopo makes this patch bad.
>
> > > - the max9286 video subdevice node is registered (on R-Car) by
> > > __v4l2_device_register_subdev_nodes() called by the root notifier
> > > complete() callback
> > >
> > > - The video_device created by __v4l2_device_register_subdev_nodes()
> > > doesn't initialize any lock
> > >
> > > What am I missing ?
> >
> > One of the fun idiosyncrasies of V4L2 :-)
> >
> > The lock comes from and are initialized by the video device used to
> > register the V4L2 async notifier. Every subdevice created is bound to a
> > vdev this way, and for example this is the vdev that events get routed
> > to.
>
> That doesn't seem right to me, could you point to the corresponding code
I was wrong it's the v4l2_device and not the vdev that is used for
events. When an sd generates an event with the call chain,
v4l2_subdev_notify_event(priv->sd, ..)
v4l2_subdev_notify(priv->sd)
priv->sd->v4l2_dev->notify()
And v4l2_dev is the one passed to v4l2_async_notifier_register() and set
in the async logic by
v4l2_async_register_subdev() OR v4l2_async_notifier_try_all_subdevs()
v4l2_async_match_notify()
v4l2_device_register_subdev()
sd->v4l2_dev = v4l2_dev
> ?
>
> > I assume this dates back pre the media-graph where every subdevice could
> > be associated with a single vdev at probe time. With the media graph
> > this makes little sens and IMHO should really be reworked. I tried once
> > but it turned out to be a lot of work that I did not have time for at
> > the time.
>
> The video_device above is the one corresponding to the V4L2 subdev
> device node (when the MC API was developed, I attempted to split the
> device node handling out of video_device, to avoid embedding a full
> video_device in v4l2_subdev, but that was rejected).
I'm sorry that got rejected. If you had gotten your way I wound not have
made the mistake and looked the fool by mixing between vdev and v4l2_dev
in this mail :-)
>
> > > > Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
> > > > ---
> > > > drivers/media/i2c/max9286.c | 10 ----------
> > > > 1 file changed, 10 deletions(-)
> > > >
> > > > diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
> > > > index 1aa2c58fd38c5d2b..b1d11a50d6e53ecc 100644
> > > > --- a/drivers/media/i2c/max9286.c
> > > > +++ b/drivers/media/i2c/max9286.c
> > > > @@ -18,7 +18,6 @@
> > > > #include <linux/i2c.h>
> > > > #include <linux/i2c-mux.h>
> > > > #include <linux/module.h>
> > > > -#include <linux/mutex.h>
> > > > #include <linux/of_graph.h>
> > > > #include <linux/regulator/consumer.h>
> > > > #include <linux/slab.h>
> > > > @@ -173,9 +172,6 @@ struct max9286_priv {
> > > >
> > > > struct v4l2_mbus_framefmt fmt[MAX9286_N_SINKS];
> > > >
> > > > - /* Protects controls and fmt structures */
> > > > - struct mutex mutex;
> > > > -
> > > > unsigned int nsources;
> > > > unsigned int source_mask;
> > > > unsigned int route_mask;
> > > > @@ -768,9 +764,7 @@ static int max9286_set_fmt(struct v4l2_subdev *sd,
> > > > if (!cfg_fmt)
> > > > return -EINVAL;
> > > >
> > > > - mutex_lock(&priv->mutex);
> > > > *cfg_fmt = format->format;
> > > > - mutex_unlock(&priv->mutex);
>
> On a side note, the usual practice is to use the same lock to prevent
> the active format from being changed during streaming.
>
> > > >
> > > > return 0;
> > > > }
> > > > @@ -796,9 +790,7 @@ static int max9286_get_fmt(struct v4l2_subdev *sd,
> > > > if (!cfg_fmt)
> > > > return -EINVAL;
> > > >
> > > > - mutex_lock(&priv->mutex);
> > > > format->format = *cfg_fmt;
> > > > - mutex_unlock(&priv->mutex);
> > > >
> > > > return 0;
> > > > }
> > > > @@ -1259,8 +1251,6 @@ static int max9286_probe(struct i2c_client *client)
> > > > if (!priv)
> > > > return -ENOMEM;
> > > >
> > > > - mutex_init(&priv->mutex);
> > > > -
> > > > priv->client = client;
> > > > i2c_set_clientdata(client, priv);
> > > >
>
> --
> Regards,
>
> Laurent Pinchart
--
Regards,
Niklas Söderlund
