RE: [PATCH] wifi: rtw89: use FIELD_PREP to fill MAC quota value

[Ping-Ke Shih <pkshih@realtek.com>]

> -----Original Message-----
> From: Kalle Valo <kvalo@kernel.org>
> Sent: Monday, November 7, 2022 8:29 PM
> To: Ping-Ke Shih <pkshih@realtek.com>
> Cc: linux-wireless@vger.kernel.org
> Subject: Re: [PATCH] wifi: rtw89: use FIELD_PREP to fill MAC quota value
> 
> Ping-Ke Shih <pkshih@realtek.com> writes:
> 
> > Coverity reported shift 16 bits could cause sign extension and might get
> > an unexpected value. Since the input values are predefined and no this
> > kind of case, original code is safe so far. But, still changing them to
> > use FIELD_PREP() will be more clear and prevent mistakes in the future.
> >
> > The original message of Coverity is:
> >   Suspicious implicit sign extension: "max_cfg->cma0_dma" with type "u16"
> >   (16 bits, unsigned) is promoted in "max_cfg->cma0_dma << 16" to type
> >   "int" (32 bits, signed), then sign-extended to type "unsigned long"
> >   (64 bits, unsigned).  If "max_cfg->cma0_dma << 16" is greater than
> >   0x7FFFFFFF, the upper bits of the result will all be 1."
> >
> > Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
> > Addresses-Coverity-ID: 1527095 ("Integer handling issues")
> > Fixes: e3ec7017f6a2 ("rtw89: add Realtek 802.11ax driver")
> > Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
> > ---
> >  drivers/net/wireless/realtek/rtw89/mac.c | 6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/net/wireless/realtek/rtw89/mac.c b/drivers/net/wireless/realtek/rtw89/mac.c
> > index bb49033b587d2..11081dfdfb172 100644
> > --- a/drivers/net/wireless/realtek/rtw89/mac.c
> > +++ b/drivers/net/wireless/realtek/rtw89/mac.c
> > @@ -1487,10 +1487,8 @@ static int dle_mix_cfg(struct rtw89_dev *rtwdev, const struct rtw89_dle_mem *cfg
> >  #define INVALID_QT_WCPU U16_MAX
> >  #define SET_QUOTA_VAL(_min_x, _max_x, _module, _idx)			\
> >  	do {								\
> > -		val = ((_min_x) &					\
> > -		       B_AX_ ## _module ## _MIN_SIZE_MASK) |		\
> > -		      (((_max_x) << 16) &				\
> > -		       B_AX_ ## _module ## _MAX_SIZE_MASK);		\
> > +		val = FIELD_PREP(B_AX_ ## _module ## _MIN_SIZE_MASK, _min_x) | \
> > +		      FIELD_PREP(B_AX_ ## _module ## _MAX_SIZE_MASK, _max_x);  \
> 
> BTW in wireless nowadays the preference is to use u32_encode_bits() & co
> instead of FIELD_PREP(). Not an issue for this patch, just wanted to
> mention anyway.
> 

I can practice to use u32_encode_bits() from this patch. Will send v2.

Ping-Ke