Re: [PATCH v6 12/26] bitfield: Add less-checking __FIELD_{GET,PREP}()

Re: [PATCH v6 12/26] bitfield: Add less-checking __FIELD_{GET,PREP}()

[Geert Uytterhoeven]

Hi Andy,

On Thu, 6 Nov 2025 at 17:09, Andy Shevchenko
<andriy.shevchenko@intel.com> wrote:
> On Thu, Nov 06, 2025 at 03:49:03PM +0100, Geert Uytterhoeven wrote:
> > On Thu, 6 Nov 2025 at 15:44, Andy Shevchenko
> > <andriy.shevchenko@intel.com> wrote:
> > > On Thu, Nov 06, 2025 at 02:34:00PM +0100, Geert Uytterhoeven wrote:
> > > > The BUILD_BUG_ON_MSG() check against "~0ull" works only with "unsigned
> > > > (long) long" _mask types.  For constant masks, that condition is usually
> > > > met, as GENMASK() yields an UL value.  The few places where the
> > > > constant mask is stored in an intermediate variable were fixed by
> > > > changing the variable type to u64 (see e.g. [1] and [2]).
> > > >
> > > > However, for non-constant masks, smaller unsigned types should be valid,
> > > > too, but currently lead to "result of comparison of constant
> > > > 18446744073709551615 with expression of type ... is always
> > > > false"-warnings with clang and W=1.
> > > >
> > > > Hence refactor the __BF_FIELD_CHECK() helper, and factor out
> > > > __FIELD_{GET,PREP}().  The later lack the single problematic check, but
> > > > are otherwise identical to FIELD_{GET,PREP}(), and are intended to be
> > > > used in the fully non-const variants later.

> > > > +     BUILD_BUG_ON_MSG(__bf_cast_unsigned(mask, mask) >               \
> > > > +                      __bf_cast_unsigned(reg, ~0ull),                \
> > > > +                      pfx "type of reg too small for mask")
> > >
> > > Perhaps we may convert this (and others?) to static_assert():s at some point?
> >
> > Nick tried that before, without success:
> > https://lore.kernel.org/all/CAKwvOdm_prtk1UQNJQGidZm44Lk582S3p=of0y46+rVjnSgXJg@mail.gmail.com
>
> Ah, this is unfortunate.

Of course, it might be an actual bug in the i915 driver...

The extra checking in field_prep() in case the compiler can
determine that the mask is a constant already found a possible bug
in drivers/net/wireless/realtek/rtw89/core.c:rtw89_roc_end():

    rtw89_write32_mask(rtwdev, reg, B_AX_RX_FLTR_CFG_MASK, rtwdev->hal.rx_fltr);

drivers/net/wireless/realtek/rtw89/reg.h:

    #define B_AX_RX_MPDU_MAX_LEN_MASK GENMASK(21, 16)
    #define B_AX_RX_FLTR_CFG_MASK ((u32)~B_AX_RX_MPDU_MAX_LEN_MASK)

so it looks like B_AX_RX_FLTR_CFG_MASK is not the proper mask for
this operation...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

RE: [PATCH v6 12/26] bitfield: Add less-checking __FIELD_{GET,PREP}()

[Ping-Ke Shih]

Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> Hi Andy,
> 
> On Thu, 6 Nov 2025 at 17:09, Andy Shevchenko
> <andriy.shevchenko@intel.com> wrote:
> > On Thu, Nov 06, 2025 at 03:49:03PM +0100, Geert Uytterhoeven wrote:
> > > On Thu, 6 Nov 2025 at 15:44, Andy Shevchenko
> > > <andriy.shevchenko@intel.com> wrote:
> > > > On Thu, Nov 06, 2025 at 02:34:00PM +0100, Geert Uytterhoeven wrote:
> > > > > The BUILD_BUG_ON_MSG() check against "~0ull" works only with "unsigned
> > > > > (long) long" _mask types.  For constant masks, that condition is usually
> > > > > met, as GENMASK() yields an UL value.  The few places where the
> > > > > constant mask is stored in an intermediate variable were fixed by
> > > > > changing the variable type to u64 (see e.g. [1] and [2]).
> > > > >
> > > > > However, for non-constant masks, smaller unsigned types should be valid,
> > > > > too, but currently lead to "result of comparison of constant
> > > > > 18446744073709551615 with expression of type ... is always
> > > > > false"-warnings with clang and W=1.
> > > > >
> > > > > Hence refactor the __BF_FIELD_CHECK() helper, and factor out
> > > > > __FIELD_{GET,PREP}().  The later lack the single problematic check, but
> > > > > are otherwise identical to FIELD_{GET,PREP}(), and are intended to be
> > > > > used in the fully non-const variants later.
> 
> > > > > +     BUILD_BUG_ON_MSG(__bf_cast_unsigned(mask, mask) >               \
> > > > > +                      __bf_cast_unsigned(reg, ~0ull),                \
> > > > > +                      pfx "type of reg too small for mask")
> > > >
> > > > Perhaps we may convert this (and others?) to static_assert():s at some point?
> > >
> > > Nick tried that before, without success:
> > > https://lore.kernel.org/all/CAKwvOdm_prtk1UQNJQGidZm44Lk582S3p=of0y46+rVjnSgXJg@mail.gmail.com
> >
> > Ah, this is unfortunate.
> 
> Of course, it might be an actual bug in the i915 driver...
> 
> The extra checking in field_prep() in case the compiler can
> determine that the mask is a constant already found a possible bug
> in drivers/net/wireless/realtek/rtw89/core.c:rtw89_roc_end():
> 
>     rtw89_write32_mask(rtwdev, reg, B_AX_RX_FLTR_CFG_MASK, rtwdev->hal.rx_fltr);
> 
> drivers/net/wireless/realtek/rtw89/reg.h:
> 
>     #define B_AX_RX_MPDU_MAX_LEN_MASK GENMASK(21, 16)
>     #define B_AX_RX_FLTR_CFG_MASK ((u32)~B_AX_RX_MPDU_MAX_LEN_MASK)
> 
> so it looks like B_AX_RX_FLTR_CFG_MASK is not the proper mask for
> this operation...

The purpose of the statements is to update values excluding bits of
B_AX_RX_MPDU_MAX_LEN_MASK. The use of B_AX_RX_FLTR_CFG_MASK is tricky, but
the operation is correct because bit 0 is set, so __ffs(mask) returns 0 in
rtw89_write32_mask(). Then, operation looks like

   orig = read(reg);
   new = (orig & ~mask) | (data & mask);
   write(new);

Since we don't use FIELD_{GET,PREP} macros with B_AX_RX_FLTR_CFG_MASK, how
can you find the problem? Please guide us. Thanks. 

Ping-Ke

Re: [PATCH v6 12/26] bitfield: Add less-checking __FIELD_{GET,PREP}()

[Andy Shevchenko]

On Fri, Nov 7, 2025 at 3:16 AM Ping-Ke Shih <pkshih@realtek.com> wrote:
>
> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Thu, 6 Nov 2025 at 17:09, Andy Shevchenko
> > <andriy.shevchenko@intel.com> wrote:
> > > On Thu, Nov 06, 2025 at 03:49:03PM +0100, Geert Uytterhoeven wrote:
> > > > On Thu, 6 Nov 2025 at 15:44, Andy Shevchenko
> > > > <andriy.shevchenko@intel.com> wrote:
> > > > > On Thu, Nov 06, 2025 at 02:34:00PM +0100, Geert Uytterhoeven wrote:
> > > > > > The BUILD_BUG_ON_MSG() check against "~0ull" works only with "unsigned
> > > > > > (long) long" _mask types.  For constant masks, that condition is usually
> > > > > > met, as GENMASK() yields an UL value.  The few places where the
> > > > > > constant mask is stored in an intermediate variable were fixed by
> > > > > > changing the variable type to u64 (see e.g. [1] and [2]).
> > > > > >
> > > > > > However, for non-constant masks, smaller unsigned types should be valid,
> > > > > > too, but currently lead to "result of comparison of constant
> > > > > > 18446744073709551615 with expression of type ... is always
> > > > > > false"-warnings with clang and W=1.
> > > > > >
> > > > > > Hence refactor the __BF_FIELD_CHECK() helper, and factor out
> > > > > > __FIELD_{GET,PREP}().  The later lack the single problematic check, but
> > > > > > are otherwise identical to FIELD_{GET,PREP}(), and are intended to be
> > > > > > used in the fully non-const variants later.
> >
> > > > > > +     BUILD_BUG_ON_MSG(__bf_cast_unsigned(mask, mask) >               \
> > > > > > +                      __bf_cast_unsigned(reg, ~0ull),                \
> > > > > > +                      pfx "type of reg too small for mask")
> > > > >
> > > > > Perhaps we may convert this (and others?) to static_assert():s at some point?
> > > >
> > > > Nick tried that before, without success:
> > > > https://lore.kernel.org/all/CAKwvOdm_prtk1UQNJQGidZm44Lk582S3p=of0y46+rVjnSgXJg@mail.gmail.com
> > >
> > > Ah, this is unfortunate.
> >
> > Of course, it might be an actual bug in the i915 driver...
> >
> > The extra checking in field_prep() in case the compiler can
> > determine that the mask is a constant already found a possible bug
> > in drivers/net/wireless/realtek/rtw89/core.c:rtw89_roc_end():
> >
> >     rtw89_write32_mask(rtwdev, reg, B_AX_RX_FLTR_CFG_MASK, rtwdev->hal.rx_fltr);
> >
> > drivers/net/wireless/realtek/rtw89/reg.h:
> >
> >     #define B_AX_RX_MPDU_MAX_LEN_MASK GENMASK(21, 16)
> >     #define B_AX_RX_FLTR_CFG_MASK ((u32)~B_AX_RX_MPDU_MAX_LEN_MASK)
> >
> > so it looks like B_AX_RX_FLTR_CFG_MASK is not the proper mask for
> > this operation...
>
> The purpose of the statements is to update values excluding bits of
> B_AX_RX_MPDU_MAX_LEN_MASK. The use of B_AX_RX_FLTR_CFG_MASK is tricky, but
> the operation is correct because bit 0 is set, so __ffs(mask) returns 0 in
> rtw89_write32_mask(). Then, operation looks like
>
>    orig = read(reg);
>    new = (orig & ~mask) | (data & mask);
>    write(new);
>
> Since we don't use FIELD_{GET,PREP} macros with B_AX_RX_FLTR_CFG_MASK, how
> can you find the problem? Please guide us. Thanks.

Isn't FIELD_MODIFY() what you want to use?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v6 12/26] bitfield: Add less-checking __FIELD_{GET,PREP}()

[Geert Uytterhoeven]

Hi Ping-Ke,

On Fri, 7 Nov 2025 at 02:16, Ping-Ke Shih <pkshih@realtek.com> wrote:
> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > The extra checking in field_prep() in case the compiler can
> > determine that the mask is a constant already found a possible bug
> > in drivers/net/wireless/realtek/rtw89/core.c:rtw89_roc_end():
> >
> >     rtw89_write32_mask(rtwdev, reg, B_AX_RX_FLTR_CFG_MASK, rtwdev->hal.rx_fltr);
> >
> > drivers/net/wireless/realtek/rtw89/reg.h:
> >
> >     #define B_AX_RX_MPDU_MAX_LEN_MASK GENMASK(21, 16)
> >     #define B_AX_RX_FLTR_CFG_MASK ((u32)~B_AX_RX_MPDU_MAX_LEN_MASK)
> >
> > so it looks like B_AX_RX_FLTR_CFG_MASK is not the proper mask for
> > this operation...
>
> The purpose of the statements is to update values excluding bits of
> B_AX_RX_MPDU_MAX_LEN_MASK. The use of B_AX_RX_FLTR_CFG_MASK is tricky, but
> the operation is correct because bit 0 is set, so __ffs(mask) returns 0 in
> rtw89_write32_mask(). Then, operation looks like
>
>    orig = read(reg);
>    new = (orig & ~mask) | (data & mask);
>    write(new);

Thanks for your quick confirmation!
So the intention really is to clear bits 22-31, and write the rx_fltr
value to bits 0-15?

if the clearing is not needed, it would be better to use
#define B_AX_RX_FLTR_CFG_MASK GENMASK(15, 0)

If the clearing is needed, I still think it would be better to
change B_AX_RX_FLTR_CFG_MASK, and split the clearing off in a separate
operation, to make it more explicit and obvious for the casual reader.

> Since we don't use FIELD_{GET,PREP} macros with B_AX_RX_FLTR_CFG_MASK, how
> can you find the problem? Please guide us. Thanks.

I still have "[PATCH/RFC 17/17] rtw89: Use bitfield helpers"
https://lore.kernel.org/all/f7b81122f7596fa004188bfae68f25a68c2d2392.1637592133.git.geert+renesas@glider.be/
in my local tree, which started flagging the use of a discontiguous
mask with the improved checking in field_prep().

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

RE: [PATCH v6 12/26] bitfield: Add less-checking __FIELD_{GET,PREP}()

[Ping-Ke Shih]

Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> Hi Ping-Ke,
> 
> On Fri, 7 Nov 2025 at 02:16, Ping-Ke Shih <pkshih@realtek.com> wrote:
> > Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > The extra checking in field_prep() in case the compiler can
> > > determine that the mask is a constant already found a possible bug
> > > in drivers/net/wireless/realtek/rtw89/core.c:rtw89_roc_end():
> > >
> > >     rtw89_write32_mask(rtwdev, reg, B_AX_RX_FLTR_CFG_MASK, rtwdev->hal.rx_fltr);
> > >
> > > drivers/net/wireless/realtek/rtw89/reg.h:
> > >
> > >     #define B_AX_RX_MPDU_MAX_LEN_MASK GENMASK(21, 16)
> > >     #define B_AX_RX_FLTR_CFG_MASK ((u32)~B_AX_RX_MPDU_MAX_LEN_MASK)
> > >
> > > so it looks like B_AX_RX_FLTR_CFG_MASK is not the proper mask for
> > > this operation...
> >
> > The purpose of the statements is to update values excluding bits of
> > B_AX_RX_MPDU_MAX_LEN_MASK. The use of B_AX_RX_FLTR_CFG_MASK is tricky, but
> > the operation is correct because bit 0 is set, so __ffs(mask) returns 0 in
> > rtw89_write32_mask(). Then, operation looks like
> >
> >    orig = read(reg);
> >    new = (orig & ~mask) | (data & mask);
> >    write(new);
> 
> Thanks for your quick confirmation!
> So the intention really is to clear bits 22-31, and write the rx_fltr
> value to bits 0-15?
> 
> if the clearing is not needed, it would be better to use
> #define B_AX_RX_FLTR_CFG_MASK GENMASK(15, 0)

But it should be 
#define B_AX_RX_FLTR_CFG_MASK (GENMASK(31, 22) | GENMASK(15, 0))

Originally (with bug) we just backup rx_fltr and write whole 32-bits back,
but it's incorrect to modify GENMASK(21, 16) which is written by another
code.

One way is to implement a special function to replace
  rtw89_write32_mask(rtwdev, reg, B_AX_RX_FLTR_CFG_MASK, rtwdev->hal.rx_fltr);
Such as
  rtw89_write_rx_flter(rtwdev, rtwdev->hal.rx_fltr)
  {
    orig = read(reg);
    new = (orig & ~mask) | (data & mask);
    write(new);
  }

Another way is that I add value of B_AX_RX_MPDU_MAX_LEN_MASK into
rtwdev->hal.rx_fltr. Then, just write whole 32-bit, no need mask.

> 
> If the clearing is needed, I still think it would be better to
> change B_AX_RX_FLTR_CFG_MASK, and split the clearing off in a separate
> operation, to make it more explicit and obvious for the casual reader.
> 
> > Since we don't use FIELD_{GET,PREP} macros with B_AX_RX_FLTR_CFG_MASK, how
> > can you find the problem? Please guide us. Thanks.
> 
> I still have "[PATCH/RFC 17/17] rtw89: Use bitfield helpers"
> https://lore.kernel.org/all/f7b81122f7596fa004188bfae68f25a68c2d2392.1637592133.git.geert+renesas@glid
> er.be/
> in my local tree, which started flagging the use of a discontiguous
> mask with the improved checking in field_prep().

Got it. You are doing "Non-const bitfield helper conversions". 

Ping-Ke

RE: [PATCH v6 12/26] bitfield: Add less-checking __FIELD_{GET,PREP}()

[Ping-Ke Shih]

Hi Geert,

Ping-Ke Shih <pkshih@realtek.com> wrote:
> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > Hi Ping-Ke,
> >
> > On Fri, 7 Nov 2025 at 02:16, Ping-Ke Shih <pkshih@realtek.com> wrote:
> > > Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > > The extra checking in field_prep() in case the compiler can
> > > > determine that the mask is a constant already found a possible bug
> > > > in drivers/net/wireless/realtek/rtw89/core.c:rtw89_roc_end():
> > > >
> > > >     rtw89_write32_mask(rtwdev, reg, B_AX_RX_FLTR_CFG_MASK, rtwdev->hal.rx_fltr);
> > > >
> > > > drivers/net/wireless/realtek/rtw89/reg.h:
> > > >
> > > >     #define B_AX_RX_MPDU_MAX_LEN_MASK GENMASK(21, 16)
> > > >     #define B_AX_RX_FLTR_CFG_MASK ((u32)~B_AX_RX_MPDU_MAX_LEN_MASK)
> > > >
> > > > so it looks like B_AX_RX_FLTR_CFG_MASK is not the proper mask for
> > > > this operation...
> > >
> > > The purpose of the statements is to update values excluding bits of
> > > B_AX_RX_MPDU_MAX_LEN_MASK. The use of B_AX_RX_FLTR_CFG_MASK is tricky, but
> > > the operation is correct because bit 0 is set, so __ffs(mask) returns 0 in
> > > rtw89_write32_mask(). Then, operation looks like
> > >
> > >    orig = read(reg);
> > >    new = (orig & ~mask) | (data & mask);
> > >    write(new);
> >
> > Thanks for your quick confirmation!
> > So the intention really is to clear bits 22-31, and write the rx_fltr
> > value to bits 0-15?
> >
> > if the clearing is not needed, it would be better to use
> > #define B_AX_RX_FLTR_CFG_MASK GENMASK(15, 0)
> 
> But it should be
> #define B_AX_RX_FLTR_CFG_MASK (GENMASK(31, 22) | GENMASK(15, 0))
> 
> Originally (with bug) we just backup rx_fltr and write whole 32-bits back,
> but it's incorrect to modify GENMASK(21, 16) which is written by another
> code.
> 
> One way is to implement a special function to replace
>   rtw89_write32_mask(rtwdev, reg, B_AX_RX_FLTR_CFG_MASK, rtwdev->hal.rx_fltr);
> Such as
>   rtw89_write_rx_flter(rtwdev, rtwdev->hal.rx_fltr)
>   {
>     orig = read(reg);
>     new = (orig & ~mask) | (data & mask);
>     write(new);
>   }
> 
> Another way is that I add value of B_AX_RX_MPDU_MAX_LEN_MASK into
> rtwdev->hal.rx_fltr. Then, just write whole 32-bit, no need mask.
> 
> >
> > If the clearing is needed, I still think it would be better to
> > change B_AX_RX_FLTR_CFG_MASK, and split the clearing off in a separate
> > operation, to make it more explicit and obvious for the casual reader.

I missed this paragraph last week, but that is like my thought.
Then I spin a RFT [1]. Please try if it can work with your changes.

[1] https://lore.kernel.org/linux-wireless/20251110023707.6272-1-pkshih@realtek.com/T/#u

> >
> > > Since we don't use FIELD_{GET,PREP} macros with B_AX_RX_FLTR_CFG_MASK, how
> > > can you find the problem? Please guide us. Thanks.
> >
> > I still have "[PATCH/RFC 17/17] rtw89: Use bitfield helpers"
> >
> https://lore.kernel.org/all/f7b81122f7596fa004188bfae68f25a68c2d2392.1637592133.git.geert+renesas@glid
> > er.be/
> > in my local tree, which started flagging the use of a discontiguous
> > mask with the improved checking in field_prep().
> 
> Got it. You are doing "Non-const bitfield helper conversions".
> 
> Ping-Ke

Re: [PATCH v6 12/26] bitfield: Add less-checking __FIELD_{GET,PREP}()

[Geert Uytterhoeven]

Hi Ady,

On Fri, 7 Nov 2025 at 09:00, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> On Fri, Nov 7, 2025 at 3:16 AM Ping-Ke Shih <pkshih@realtek.com> wrote:
> > Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > On Thu, 6 Nov 2025 at 17:09, Andy Shevchenko
> > > <andriy.shevchenko@intel.com> wrote:
> > > > On Thu, Nov 06, 2025 at 03:49:03PM +0100, Geert Uytterhoeven wrote:
> > > > > On Thu, 6 Nov 2025 at 15:44, Andy Shevchenko
> > > > > <andriy.shevchenko@intel.com> wrote:
> > > > > > On Thu, Nov 06, 2025 at 02:34:00PM +0100, Geert Uytterhoeven wrote:
> > > > > > > The BUILD_BUG_ON_MSG() check against "~0ull" works only with "unsigned
> > > > > > > (long) long" _mask types.  For constant masks, that condition is usually
> > > > > > > met, as GENMASK() yields an UL value.  The few places where the
> > > > > > > constant mask is stored in an intermediate variable were fixed by
> > > > > > > changing the variable type to u64 (see e.g. [1] and [2]).
> > > > > > >
> > > > > > > However, for non-constant masks, smaller unsigned types should be valid,
> > > > > > > too, but currently lead to "result of comparison of constant
> > > > > > > 18446744073709551615 with expression of type ... is always
> > > > > > > false"-warnings with clang and W=1.
> > > > > > >
> > > > > > > Hence refactor the __BF_FIELD_CHECK() helper, and factor out
> > > > > > > __FIELD_{GET,PREP}().  The later lack the single problematic check, but
> > > > > > > are otherwise identical to FIELD_{GET,PREP}(), and are intended to be
> > > > > > > used in the fully non-const variants later.
> > >
> > > > > > > +     BUILD_BUG_ON_MSG(__bf_cast_unsigned(mask, mask) >               \
> > > > > > > +                      __bf_cast_unsigned(reg, ~0ull),                \
> > > > > > > +                      pfx "type of reg too small for mask")
> > > > > >
> > > > > > Perhaps we may convert this (and others?) to static_assert():s at some point?
> > > > >
> > > > > Nick tried that before, without success:
> > > > > https://lore.kernel.org/all/CAKwvOdm_prtk1UQNJQGidZm44Lk582S3p=of0y46+rVjnSgXJg@mail.gmail.com
> > > >
> > > > Ah, this is unfortunate.
> > >
> > > Of course, it might be an actual bug in the i915 driver...
> > >
> > > The extra checking in field_prep() in case the compiler can
> > > determine that the mask is a constant already found a possible bug
> > > in drivers/net/wireless/realtek/rtw89/core.c:rtw89_roc_end():
> > >
> > >     rtw89_write32_mask(rtwdev, reg, B_AX_RX_FLTR_CFG_MASK, rtwdev->hal.rx_fltr);
> > >
> > > drivers/net/wireless/realtek/rtw89/reg.h:
> > >
> > >     #define B_AX_RX_MPDU_MAX_LEN_MASK GENMASK(21, 16)
> > >     #define B_AX_RX_FLTR_CFG_MASK ((u32)~B_AX_RX_MPDU_MAX_LEN_MASK)
> > >
> > > so it looks like B_AX_RX_FLTR_CFG_MASK is not the proper mask for
> > > this operation...
> >
> > The purpose of the statements is to update values excluding bits of
> > B_AX_RX_MPDU_MAX_LEN_MASK. The use of B_AX_RX_FLTR_CFG_MASK is tricky, but
> > the operation is correct because bit 0 is set, so __ffs(mask) returns 0 in
> > rtw89_write32_mask(). Then, operation looks like
> >
> >    orig = read(reg);
> >    new = (orig & ~mask) | (data & mask);
> >    write(new);
> >
> > Since we don't use FIELD_{GET,PREP} macros with B_AX_RX_FLTR_CFG_MASK, how
> > can you find the problem? Please guide us. Thanks.
>
> Isn't FIELD_MODIFY() what you want to use?

FIELD_MODIFY() is a rather recent addition.
That is also the reason why I didn't add a non-const field_modify() yet
(I didn't want to risk delaying this series even more ;-)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds