Re: [PATCH v1] media: vivid: Add webcam parameter for (un)limited bandwidth

[Max Staudt]

Thank you Mauro for having a first look!

Questions below.


On 4/10/23 18:23, Mauro Carvalho Chehab wrote:
> IMO, instead of a parameter that just enables/disables the bandwidth
> limit, the best would be to have a parameter specifying the bandwidth
> (with 0 meaning unlimited).
>
> If not used, vivid would initialize it to dev->webcam_bandwidth_limit,
> so a read operation will show the current limit.
Up until now, the bandwidth limit is a rather arbitrary reduction of two 
interval sizes per frame size.

How would you prefer to define a limited bandwidth in this parameter? 
How would it affect the simulated camera, do you have a suggestion for a 
formula from bandwidth to frame/interval sizes offered?


> > +/* Default: limited webcam bandwidth */
> > +static bool webcam_bandwidth_limit[VIVID_MAX_DEVS] = { [0 ... (VIVID_MAX_DEVS - 1)] = true };
> > +module_param_array(webcam_bandwidth_limit, bool, NULL, 0444);
>
> I would also use 0666, to allow changing this on runtime.

I guess that's possible, though it would add complexity.

Currently we can ask for two instances, each with a different setting:

  n_devs=2 webcam_bandwidth_limit=1,0

This creates /dev/video0 which is limited, and /dev/video4 which is 
unlimited.

Maybe this already sufficiently covers the case you are looking for, and 
we can keep the complexity low? A real webcam won't suddenly offer new 
frame rates either...



Max