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SubjectRe: [PATCH v9 11/20] gpiolib: cdev: support GPIO_V2_LINE_SET_VALUES_IOCTL
On Thu, Sep 24, 2020 at 11:21:05AM +0300, Andy Shevchenko wrote:
> On Thu, Sep 24, 2020 at 10:32 AM Kent Gibson <warthog618@gmail.com> wrote:
> > On Wed, Sep 23, 2020 at 07:18:08PM +0300, Andy Shevchenko wrote:
> > > On Tue, Sep 22, 2020 at 5:36 AM Kent Gibson <warthog618@gmail.com> wrote:
> > > >
> > > > Add support for the GPIO_V2_LINE_SET_VALUES_IOCTL.
> > >
> > > > +static long linereq_set_values_unlocked(struct linereq *lr,
> > > > + struct gpio_v2_line_values *lv)
> > > > +{
> > > > + DECLARE_BITMAP(vals, GPIO_V2_LINES_MAX);
> > > > + struct gpio_desc **descs;
> > > > + unsigned int i, didx, num_set;
> > > > + int ret;
> > > > +
> > > > + bitmap_zero(vals, GPIO_V2_LINES_MAX);
> > > > + for (num_set = 0, i = 0; i < lr->num_lines; i++) {
> > > > + if (lv->mask & BIT_ULL(i)) {
> > >
> > > Similar idea
> > >
> > > DECLARE_BITMAP(mask, 64) = BITMAP_FROM_U64(lv->mask);
> > >
> > > num_set = bitmap_weight();
> > >
> >
> > I had played with this option, but bitmap_weight() counts all
> > the bits set in the mask - which considers bits >= lr->num_lines.
>
> Does it mean we have a bug in the code and no test case covered it?
> Because from the API I see the parameter nbits which should prevent
> this.
>

Probably me being thick and using nbits as the size of the mask
rather than the number of bits of interest.

Cheers,
Kent.

> > So you would need to mask lv->mask before converting it to a bitmap.
> > (I'm ok with ignoring those bits in case userspace wants to be lazy and
> > use an all 1s mask.)
>
> Can you confirm a bug in bitmap API? If it's so it's a serious one.
>
> > But since we're looping over the bitmap anyway we may as well just
> > count as we go.
> >
> > > for_each_set_bit(i, mask, lr->num_lines)
> > >
> >
> > Yeah, that should work. I vaguely recall trying this and finding it
> > generated larger object code, but I'll give it another try and if it
> > works out then include it in v10.
>
>
> --
> With Best Regards,
> Andy Shevchenko

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