Re: [PATCH v5 4/5] net: wan: fsl_qmc_hdlc: Add runtime timeslots changes support

Herve Codina
2024-02-29T16:30:47Z

Hi Andy,

On Thu, 29 Feb 2024 17:20:59 +0200
Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:

> On Thu, Feb 29, 2024 at 03:15:52PM +0100, Herve Codina wrote:
> > QMC channels support runtime timeslots changes but nothing is done at
> > the QMC HDLC driver to handle these changes.
> >
> > Use existing IFACE ioctl in order to configure the timeslots to use.
>
> ...
>
> > + bitmap_scatter(ts_mask, map, ts_mask_avail, 64);
>
> Wondering if we may have returned value more useful and hence having something like
>
> n = bitmap_scatter(...);

I thought about it.

In bitmap_{scatter,gather}(dst, src, mask, nbits), only returning the
weight of the third parameter (i.e. mask) can be efficient regarding to the
for_each_set_bit() loop done in the functions.
For dst parameter, we need to add a counter in the loop to count the number
of bit set depending on the test_bit() result. Will this be more efficient
than a call to bitmap_weight() ?

Also, in my case, the third parameter is ts_mask_avail and I don't need
its weight.

I thing users that need to have the dst or src weight should call
bitmap_weight() themselves as this is users context dependent.

bitmap_{scatter,gather}(dst, src, mask, nbits) can be improved later with
no impact to current users (except performance).

That's why I concluded to return nothing from bitmap_{scatter,gather} when
I took the old existing patches.

>
> > + if (bitmap_weight(ts_mask, 64) != bitmap_weight(map, 64)) {
>
> if (n != ...) {
>
> ?
>
> > + dev_err(qmc_hdlc->dev, "Cannot translate timeslots %64pb -> (%64pb, %64pb)\n",
> > + map, ts_mask_avail, ts_mask);
> > + return -EINVAL;
> > + }
>
> ...
>
> > + bitmap_gather(map, ts_mask, ts_mask_avail, 64);
> > +
> > + if (bitmap_weight(ts_mask, 64) != bitmap_weight(map, 64)) {
> > + dev_err(qmc_hdlc->dev, "Cannot translate timeslots (%64pb, %64pb) -> %64pb\n",
> > + ts_mask_avail, ts_mask, map);
> > + return -EINVAL;
> > + }
>
> Ditto.
>

Best regards,
Hervé