Re: [PATCH v3] media: imx319: Add imx319 camera sensor driver

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On Fri, May 25, 2018 at 4:12 PM jacopo mondi <jacopo@xxxxxxxxxx> wrote:

> Hi Tomasz,

> On Fri, May 25, 2018 at 03:18:38PM +0900, Tomasz Figa wrote:
> > On Fri, May 25, 2018 at 5:47 AM Sakari Ailus <
sakari.ailus@xxxxxxxxxxxxxxx>
> > wrote:
> >
> > > Hi Jacopo,
> >
> > > On Thu, May 24, 2018 at 10:07:38PM +0200, jacopo mondi wrote:
> > > ...
> > > > > > about that, but I wonder why setting controls should be enabled
only
> > > > > > when streaming. I would have expected runtime_pm_get/put in
> > subdevices
> > > > > > node open/close functions not only when streaming. Am I missing
> > something?
> > > > >
> > > > > You can do it either way. If powering on the sensor takes a long
> > time, then
> > > > > doing that in the open callback may be helpful as the user space
has
> > a way
> > > > > to keep the device powered.
> > > >
> > > > Ok, so I assume my comment could be ignored, assuming is fine not
> > > > being able to set control if the sensor is not streaming. Is it?
> >
> > > I'd say so. From the user's point of view, the sensor doesn't really
do
> > > anything when it's in software standby mode.
> >
> > Just to make sure we're on the same page, the code actually does nothing
> > when the sensor is not in streaming mode (i.e. powered off). When
stream is
> > being started, the V4L2 control framework will call s_ctrl for all the
> > controls in the handler to synchronize hardware state and this is when
all
> > the controls set before powering on will actually be programmed into the
> > hardware registers.

> Thanks, I had missed that part.

> I quickly tried searching for 's_ctrl' calls in the v4l2-core/ code
> and I've found nothing that invokes that in response to a streaming
> start operation. Just if you happen to have any reference handy, could
> you please point me to that part, just for my better understanding?

The driver does it itself by calling __v4l2_ctrl_handler_setup() from its
.start_streaming() callback.

Best regards,
Tomasz



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