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.
> > - 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 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).
> > > 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
