Subject: [PATCH v2] pinctrl: pinctrl-single: Fix pcs_parse_bits_in_pinctrl_entry to use __ffs than ffs

From: [email-masked] (Tony Lindgren)
Date: Fri, 15 Apr 2016 08:22:16 -0700

* Linus Walleij <[email-masked]> [160415 02:29]:
> On Thu, Apr 14, 2016 at 6:59 AM, Keerthy <[email-masked]> wrote:
> 
> > pcs_parse_bits_in_pinctrl_entry uses ffs which gives bit indices
> > ranging from 1 to MAX. This leads to a corner case where we try to request
> > the pin number = MAX and fails.
> >
> > bit_pos value is being calculted using ffs. pin_num_from_lsb uses
> > bit_pos value. pins array is populated with:
> >
> > pin + pin_num_from_lsb.
> >
> > The above is 1 more than usual bit indices as bit_pos uses ffs to compute
> > first set bit. Hence the last of the pins array is populated with the MAX
> > value and not MAX - 1 which causes error when we call pin_request.
> >
> > mask_pos is rightly calculated as ((pcs->fmask) << (bit_pos - 1))
> > Consequently val_pos and submask are correct.
> >
> > Hence use __ffs which gives (ffs(x) - 1) as the first bit set.
> >
> > fixes: 4e7e8017a8 ("pinctrl: pinctrl-single: enhance to configure multiple pins of different modules")
> > Signed-off-by: Keerthy <[email-masked]>
> > ---
> >
> > Changes in v2:
> >
> >   * Changed pcs->fshift to use __ffs instead of ffs to be consistent.
> >
> > Boot tesed on da850-evm and checked the pinctrl sysfs nodes.
> 
> Patch applied for fixes with Tony's ACK.
> 
> Should it also be tagged for stable?

Probably a good idea, I can see somebody pulling hair out because
of this in various product trees.

Regards,

Tony