Re: [PATCH v2 2/2] wifi: rtlwifi: rtl8821ae: phy: fix an undefined bitwise shift behavior

[Su Hui <suhui@xxxxxxxxxxxx>]

On 2023/11/24 19:19, Ping-Ke Shih wrote:
> On Fri, 2023-11-24 at 18:06 +0800, Su Hui wrote:
> > On 2023/11/24 16:51, Ping-Ke Shih wrote:
> > > Subject: [PATCH v2 2/2] wifi: rtlwifi: rtl8821ae: phy: fix an undefined bitwise shift behavior
> > >
> > > [...]
> > > > diff --git a/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c
> > > > b/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c
> > > > index 6df270e29e66..52ab1b0761c0 100644
> > > > --- a/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c
> > > > +++ b/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c
> > > > @@ -31,7 +31,12 @@ static u32 _rtl8821ae_phy_calculate_bit_shift(u32 bitmask)
> > > >    {
> > > >           u32 i = ffs(bitmask);
> > > >
> > > > -       return i ? i - 1 : 32;
> > > > +       if (!i) {
> > > > +               WARN_ON_ONCE(1);
> > > > +               return 0;
> > > > +       }
> > > > +
> > > > +       return i - 1;
> > > >    }
> > > Personally, I prefer to use __ffs(), because in normal case no need additional '-1',
> > > and abnormal cases should not happen.
> > Hi,  Ping-Ke
> >
> > Replace _rtl8821ae_phy_calculate_bit_shift() by __ffs(bitmask) is better,
> > but I'm not sure what callers should do when callers check bitmask is 0 before calling.
> > Maybe this check is useless?
> >
> > I can send a v3 patch if using  __ffs(bitmask) and no check for bitmask is fine.
> > Or could you send this patch if you have a better idea?
> > Thanks for your suggestion!
> Can this work to you?
Looks good to me, briefer and better!
I will send v3 soon.
> static u32 _rtl8821ae_phy_calculate_bit_shift(u32 bitmask)
> {
> 	if (WARN_ON_ONCE(!bitmask))
> 		return 0;
>
> 	return __ffs(bitmask);
> }