Re: [PATCH] media: staging: max96712: Store format in subdev active state

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Hi Laurent,

On 2024-05-10 18:27:24 +0300, Laurent Pinchart wrote:
> Hi Niklas,
> 
> On Fri, May 10, 2024 at 12:36:56PM +0200, Niklas Söderlund wrote:
> > On 2024-05-10 13:13:40 +0300, Laurent Pinchart wrote:
> > > On Fri, May 10, 2024 at 12:03:47PM +0200, Niklas Söderlund wrote:
> > > > Create and store the subdevice format in the subdevices active state.
> > > > This change do not have a huge effect on the driver as it do not yet
> > > > support changing the format.
> > > > 
> > > > Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
> > > > ---
> > > > Hello,
> > > > 
> > > > This change is mostly to align all driver used in the R-Car VIN pipeline
> > > > to use the same set of API and to make it easier to extend them in
> > > > tandem going forward.
> > > > 
> > > > This should be seen as a compliment to Jacopo's larger work in "[PATCH
> > > > v3 00/11] media: renesas: rcar-csi2: Use the subdev active state" which
> > > > updates other drivers in the VIN pipeline to use the active state.
> > > > ---
> > > >  drivers/staging/media/max96712/max96712.c | 36 +++++++++++++++++------
> > > >  1 file changed, 27 insertions(+), 9 deletions(-)
> > > > 
> > > > diff --git a/drivers/staging/media/max96712/max96712.c b/drivers/staging/media/max96712/max96712.c
> > > > index c44145284aa1..2da65ccd2c57 100644
> > > > --- a/drivers/staging/media/max96712/max96712.c
> > > > +++ b/drivers/staging/media/max96712/max96712.c
> > > > @@ -242,21 +242,34 @@ static const struct v4l2_subdev_video_ops max96712_video_ops = {
> > > >  	.s_stream = max96712_s_stream,
> > > >  };
> > > >  
> > > > -static int max96712_get_pad_format(struct v4l2_subdev *sd,
> > > > -				   struct v4l2_subdev_state *sd_state,
> > > > -				   struct v4l2_subdev_format *format)
> > > > +static int max96712_init_state(struct v4l2_subdev *sd,
> > > > +			       struct v4l2_subdev_state *state)
> > > >  {
> > > > -	format->format.width = 1920;
> > > > -	format->format.height = 1080;
> > > > -	format->format.code = MEDIA_BUS_FMT_RGB888_1X24;
> > > > -	format->format.field = V4L2_FIELD_NONE;
> > > > +	static const struct v4l2_mbus_framefmt default_fmt = {
> > > > +		.width          = 1920,
> > > > +		.height         = 1080,
> > > > +		.code           = MEDIA_BUS_FMT_RGB888_1X24,
> > > > +		.colorspace     = V4L2_COLORSPACE_SRGB,
> > > > +		.field          = V4L2_FIELD_NONE,
> > > > +		.ycbcr_enc      = V4L2_YCBCR_ENC_DEFAULT,
> > > > +		.quantization   = V4L2_QUANTIZATION_DEFAULT,
> > > > +		.xfer_func      = V4L2_XFER_FUNC_DEFAULT,
> > > > +	};
> > > > +	struct v4l2_mbus_framefmt *fmt;
> > > > +
> > > > +	fmt = v4l2_subdev_state_get_format(state, 0);
> > > > +	*fmt = default_fmt;
> > > >  
> > > >  	return 0;
> > > >  }
> > > >  
> > > > +static const struct v4l2_subdev_internal_ops max96712_internal_ops = {
> > > > +	.init_state = max96712_init_state,
> > > > +};
> > > > +
> > > >  static const struct v4l2_subdev_pad_ops max96712_pad_ops = {
> > > > -	.get_fmt = max96712_get_pad_format,
> > > > -	.set_fmt = max96712_get_pad_format,
> > > > +	.get_fmt = v4l2_subdev_get_fmt,
> > > > +	.set_fmt = v4l2_subdev_get_fmt,
> > > >  };
> > > >  
> > > >  static const struct v4l2_subdev_ops max96712_subdev_ops = {
> > > > @@ -293,6 +306,7 @@ static int max96712_v4l2_register(struct max96712_priv *priv)
> > > >  	long pixel_rate;
> > > >  	int ret;
> > > >  
> > > > +	priv->sd.internal_ops = &max96712_internal_ops;
> > > >  	v4l2_i2c_subdev_init(&priv->sd, priv->client, &max96712_subdev_ops);
> > > >  	priv->sd.flags |= V4L2_SUBDEV_FL_HAS_DEVNODE;
> > > >  	priv->sd.entity.function = MEDIA_ENT_F_VID_IF_BRIDGE;
> > > > @@ -324,6 +338,10 @@ static int max96712_v4l2_register(struct max96712_priv *priv)
> > > >  
> > > >  	v4l2_set_subdevdata(&priv->sd, priv);
> > > >  
> > > 
> > > I think it would be nice to already use the control handler lock as the
> > > active state lock. Apart from that, the patch looks good to me.
> > 
> > I also worked on this to learn a bit more about the active state API. I 
> > assume what you are asking for here is ?
> > 
> >     priv->sd.state_lock = priv->ctrl_handler.lock;
> 
> That's right.

I will send a v2 of this patch using the controller lock.

> 
> > What is the rational for using the control handler lock over the default 
> > state lock?
> 
> When there are interactions between controls and formats, using separate
> locks can lead to AB/BA deadlocks if you need to access controls from a
> context where the state is locked (e.g. calling
> v4l2_ctrl_handler_setup() at stream enable time), and access the active
> state from a context where the control handler is locked (e.g. accessing
> the state in .s_ctrl()). Using the same lock helps there, you can then
> call __v4l2_ctrl_handler_setup() at stream enable time, and get the
> state without locking it in .s_ctrl().
> 
> At some point in the not too distant future I would like to move storage
> of controls to the state. I don't know how painful that will be though,
> the control framework has grown to be a very complex beast, with lots of
> features that are not useful for MC-based drivers (such as control
> handler inheritance). I'm worried that we'll need a full rewrite...
> We'll see :-)
> 
> > I checked Jacopo's series when working on this and there he 
> > uses no lock for the R-Car CSI-2 driver and a private driver global 
> > state lock for ADV748x.
> 
> For the CSI-2 RX driver, that's because it doesn't have a control
> handler. For the ADV748x driver, that's because the control handler is
> configured to use the device-wide mutex.

Thanks for this through description of why using the control handler 
lock for the stat is a good idea. I really like your idea of trying to 
make the control framework less complex for MC-based drivers in the 
future.

> 
> > > > +	ret = v4l2_subdev_init_finalize(&priv->sd);
> > > > +	if (ret)
> > > > +		goto error;
> > > > +
> > > >  	ret = v4l2_async_register_subdev(&priv->sd);
> > > >  	if (ret < 0) {
> > > >  		dev_err(&priv->client->dev, "Unable to register subdevice\n");
> 
> -- 
> Regards,
> 
> Laurent Pinchart

-- 
Kind Regards,
Niklas Söderlund




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