Re: [PATCH v4 3/6] media: max9286: Use enabled routes to calculate pixelrate

[Jacopo Mondi <jacopo@jmondi.org>]

Hi Laurent,

On Fri, Dec 17, 2021 at 04:29:50AM +0200, Laurent Pinchart wrote:
> Hi Jacopo,
>
> Thank you for the patch.
>
> On Thu, Dec 16, 2021 at 06:47:43PM +0100, Jacopo Mondi wrote:
> > Now that the device supports routing, use the enabled routes instead
> > of the connected sources to compute the output pixel rate.
> >
> > To do so, update the route_mask after a set_routing() call with the
> > ACTIVE format, and re-calculate the pixel rate just after.
> >
> > At the same time, start and stop only the enabled routes at s_stream()
> > time.
> >
> > Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> > ---
> >  drivers/media/i2c/max9286.c | 63 ++++++++++++++++++++++++++++++-------
> >  1 file changed, 51 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
> > index eb76acdb2cd9..1395eb783dc0 100644
> > --- a/drivers/media/i2c/max9286.c
> > +++ b/drivers/media/i2c/max9286.c
> > @@ -188,8 +188,11 @@ struct max9286_priv {
> >  	struct v4l2_async_notifier notifier;
> >  };
> >
> > +#define to_index(priv, source) ((source) - &(priv)->sources[0])
> > +
> >  static struct max9286_source *next_source(struct max9286_priv *priv,
> > -					  struct max9286_source *source)
> > +					  struct max9286_source *source,
> > +					  bool routed)
> >  {
> >  	if (!source)
> >  		source = &priv->sources[0];
> > @@ -197,17 +200,27 @@ static struct max9286_source *next_source(struct max9286_priv *priv,
> >  		source++;
> >
> >  	for (; source < &priv->sources[MAX9286_NUM_GMSL]; source++) {
> > -		if (source->fwnode)
> > +		unsigned int index = to_index(priv, source);
> > +
> > +		if (!source->fwnode)
> > +			continue;
> > +
> > +		/*
> > +		 * Careful here! A very unfortunate call to set_routing() can
> > +		 * change priv->route_mask behind our back!
> > +		 */
>
> This seems error-prone. I wonder if we could instead remove route_mask
> completely, and compute it as .s_stream(1) time by walking the routes
> from the state. That would avoid storing state information in
> max9286_priv.

I wish I could, but I need an up-to-date pixelrate for the CSI-2
receiver, before it calls into s_stream(1) :(

The race window is very small (I know, if things can go wrong, they
will..) and I could protect it with a mutex ?

>
> The downside is that we'll have to pass the route mask down to functions
> called by max9286_s_stream(). At some point in the future, I'd like to
> see support for subclassing the subdev state in subdev drivers, at which
> point we will be able to cache the route_mask in the subclassed state
> when configuring routing, and reusing the cached value when starting the
> streams.
>

With the state being locked, this would prevent any race from
happening, that's right!

What about a mutex for the time being ?

> > +		if (!routed || priv->route_mask & BIT(index))
> >  			return source;
> >  	}
> >
> >  	return NULL;
> >  }
> >
> > -#define for_each_source(priv, source) \
> > -	for ((source) = NULL; ((source) = next_source((priv), (source))); )
> > +#define for_each_route(priv, source) \
> > +	for ((source) = NULL; ((source) = next_source((priv), (source), true)); )
> >
> > -#define to_index(priv, source) ((source) - &(priv)->sources[0])
> > +#define for_each_source(priv, source) \
> > +	for ((source) = NULL; ((source) = next_source((priv), (source), false)); )
> >
> >  static inline struct max9286_priv *sd_to_max9286(struct v4l2_subdev *sd)
> >  {
> > @@ -409,7 +422,7 @@ static int max9286_check_video_links(struct max9286_priv *priv)
> >  		if (ret < 0)
> >  			return -EIO;
> >
> > -		if ((ret & MAX9286_VIDEO_DETECT_MASK) == priv->source_mask)
> > +		if ((ret & MAX9286_VIDEO_DETECT_MASK) == priv->route_mask)
> >  			break;
> >
> >  		usleep_range(350, 500);
> > @@ -493,9 +506,10 @@ static int max9286_check_config_link(struct max9286_priv *priv,
> >  static int max9286_set_pixelrate(struct max9286_priv *priv)
> >  {
> >  	struct max9286_source *source = NULL;
> > +	unsigned int num_routes = 0;
> >  	u64 pixelrate = 0;
> >
> > -	for_each_source(priv, source) {
> > +	for_each_route(priv, source) {
> >  		struct v4l2_ctrl *ctrl;
> >  		u64 source_rate = 0;
> >
> > @@ -516,6 +530,8 @@ static int max9286_set_pixelrate(struct max9286_priv *priv)
> >  				"Unable to calculate pixel rate\n");
> >  			return -EINVAL;
> >  		}
> > +
> > +		num_routes++;
> >  	}
> >
> >  	if (!pixelrate) {
> > @@ -529,7 +545,7 @@ static int max9286_set_pixelrate(struct max9286_priv *priv)
> >  	 * by the number of available sources.
> >  	 */
> >  	return v4l2_ctrl_s_ctrl_int64(priv->pixelrate,
> > -				      pixelrate * priv->nsources);
> > +				      pixelrate * num_routes);
> >  }
> >
> >  static int max9286_notify_bound(struct v4l2_async_notifier *notifier,
> > @@ -691,8 +707,8 @@ static int max9286_s_stream(struct v4l2_subdev *sd, int enable)
> >  		 */
> >  		max9286_i2c_mux_open(priv);
> >
> > -		/* Start all cameras. */
> > -		for_each_source(priv, source) {
> > +		/* Start cameras. */
> > +		for_each_route(priv, source) {
> >  			ret = v4l2_subdev_call(source->sd, video, s_stream, 1);
> >  			if (ret)
> >  				return ret;
> > @@ -733,8 +749,8 @@ static int max9286_s_stream(struct v4l2_subdev *sd, int enable)
> >  	} else {
> >  		max9286_write(priv, 0x15, MAX9286_VCTYPE | MAX9286_0X15_RESV);
> >
> > -		/* Stop all cameras. */
> > -		for_each_source(priv, source)
> > +		/* Stop cameras. */
> > +		for_each_route(priv, source)
> >  			v4l2_subdev_call(source->sd, video, s_stream, 0);
> >
> >  		max9286_i2c_mux_close(priv);
> > @@ -912,6 +928,29 @@ static int max9286_set_routing(struct v4l2_subdev *sd,
> >  	v4l2_subdev_lock_state(state);
> >
> >  	ret = _max9286_set_routing(sd, state, routing);
> > +	if (ret)
> > +		goto out;
> > +
> > +	if (which == V4L2_SUBDEV_FORMAT_TRY)
> > +		goto out;
> > +
> > +	/*
> > +	 * Update the active routes mask and the pixel rate according to the
> > +	 * routed sources.
> > +	 */
> > +	priv->route_mask = 0;
> > +	for (i = 0; i < routing->num_routes; ++i) {
> > +		struct v4l2_subdev_route *route = &routing->routes[i];
> > +
> > +		if (!(route->flags & V4L2_SUBDEV_ROUTE_FL_ACTIVE))
> > +			continue;
> > +
> > +		priv->route_mask |= BIT(route->sink_pad);
> > +	}
> > +
> > +	max9286_set_pixelrate(priv);
> > +
> > +out:
> >  	v4l2_subdev_unlock_state(state);
> >
> >  	return ret;
>
> --
> Regards,
>
> Laurent Pinchart