+ Catalin Marinas, ARM maillist Hi Catalin and everyone, Anshuman Khandual asked me to merge GENMASK_U128() saying it's important for ARM to stabilize API. While it's a dead code, I accepted his patch as he promised to add users shortly. Now it's more than half a year since that. There's no users, and no feedback from Anshuman. Can you please tell if you still need the macro? I don't want to undercut your development, but if you don't need 128-bit genmasks there's no reason to have a dead code in the uapi. Thanks, Yury On Wed, Mar 05, 2025 at 10:22:47AM -0500, Yury Norov wrote: > + Anshuman Khandual <anshuman.khandual@xxxxxxx> > > Anshuman, > > I merged your GENMASK_U128() because you said it's important for your > projects, and that it will get used in the kernel soon. > > Now it's in the kernel for more than 6 month, but no users were added. > Can you clarify if you still need it, and if so why it's not used? > > As you see, people add another fixed-types GENMASK() macros, and their > implementation differ from GENMASK_U128(). > > My second concern is that __GENMASK_U128() is declared in uapi, while > the general understanding for other fixed-type genmasks is that they > are not exported to users. Do you need this macro to be exported to > userspace? Can you show how and where it is used there? > > Thanks, > Yury > > > On Wed, Mar 05, 2025 at 10:00:15PM +0900, Vincent Mailhol via B4 Relay wrote: > > From: Yury Norov <yury.norov@xxxxxxxxx> > > > > Add __GENMASK_t() which generalizes __GENMASK() to support different > > types, and implement fixed-types versions of GENMASK() based on it. > > The fixed-type version allows more strict checks to the min/max values > > accepted, which is useful for defining registers like implemented by > > i915 and xe drivers with their REG_GENMASK*() macros. > > > > The strict checks rely on shift-count-overflow compiler check to fail > > the build if a number outside of the range allowed is passed. > > Example: > > > > #define FOO_MASK GENMASK_U32(33, 4) > > > > will generate a warning like: > > > > ../include/linux/bits.h:41:31: error: left shift count >= width of type [-Werror=shift-count-overflow] > > 41 | (((t)~0ULL - ((t)(1) << (l)) + 1) & \ > > | ^~ > > > > Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx> > > Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx> > > Acked-by: Jani Nikula <jani.nikula@xxxxxxxxx> > > Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> > > --- > > Changelog: > > > > v3 -> v4: > > > > - The v3 is one year old. Meanwhile people started using > > __GENMASK() directly. So instead of generalizing __GENMASK() to > > support different types, add a new GENMASK_t(). > > > > - replace ~0ULL by ~_ULL(0). Otherwise, __GENMASK_t() would fail > > in asm code. > > > > - Make GENMASK_U8() and GENMASK_U16() return an unsigned int. In > > v3, due to the integer promotion rules, these were returning a > > signed integer. By casting these to unsigned int, at least the > > signedness is kept. > > --- > > include/linux/bitops.h | 1 - > > include/linux/bits.h | 33 +++++++++++++++++++++++++++++---- > > 2 files changed, 29 insertions(+), 5 deletions(-) > > > > diff --git a/include/linux/bitops.h b/include/linux/bitops.h > > index c1cb53cf2f0f8662ed3e324578f74330e63f935d..9be2d50da09a417966b3d11c84092bb2f4cd0bef 100644 > > --- a/include/linux/bitops.h > > +++ b/include/linux/bitops.h > > @@ -8,7 +8,6 @@ > > > > #include <uapi/linux/kernel.h> > > > > -#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE) > > #define BITS_TO_LONGS(nr) __KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(long)) > > #define BITS_TO_U64(nr) __KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(u64)) > > #define BITS_TO_U32(nr) __KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(u32)) > > diff --git a/include/linux/bits.h b/include/linux/bits.h > > index 5f68980a1b98d771426872c74d7b5c0f79e5e802..f202e46d2f4b7899c16d975120f3fa3ae41556ae 100644 > > --- a/include/linux/bits.h > > +++ b/include/linux/bits.h > > @@ -12,6 +12,7 @@ > > #define BIT_ULL_MASK(nr) (ULL(1) << ((nr) % BITS_PER_LONG_LONG)) > > #define BIT_ULL_WORD(nr) ((nr) / BITS_PER_LONG_LONG) > > #define BITS_PER_BYTE 8 > > +#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE) > > > > /* > > * Create a contiguous bitmask starting at bit position @l and ending at > > @@ -25,14 +26,38 @@ > > > > #define GENMASK_INPUT_CHECK(h, l) BUILD_BUG_ON_ZERO(const_true((l) > (h))) > > > > -#define GENMASK(h, l) \ > > - (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) > > -#define GENMASK_ULL(h, l) \ > > - (GENMASK_INPUT_CHECK(h, l) + __GENMASK_ULL(h, l)) > > +/* > > + * Generate a mask for the specified type @t. Additional checks are made to > > + * guarantee the value returned fits in that type, relying on > > + * shift-count-overflow compiler check to detect incompatible arguments. > > + * For example, all these create build errors or warnings: > > + * > > + * - GENMASK(15, 20): wrong argument order > > + * - GENMASK(72, 15): doesn't fit unsigned long > > + * - GENMASK_U32(33, 15): doesn't fit in a u32 > > + */ > > +#define GENMASK_t(t, h, l) \ > > + (GENMASK_INPUT_CHECK(h, l) + \ > > + (((t)~ULL(0) - ((t)1 << (l)) + 1) & \ > > + ((t)~ULL(0) >> (BITS_PER_TYPE(t) - 1 - (h))))) > > + > > +#define GENMASK(h, l) GENMASK_t(unsigned long, h, l) > > +#define GENMASK_ULL(h, l) GENMASK_t(unsigned long long, h, l) > > > > /* > > * Missing asm support > > * > > + * __GENMASK_U*() depends on BITS_PER_TYPE() which would not work in the asm > > + * code as BITS_PER_TYPE() relies on sizeof(), something not available in > > + * asm. Nethertheless, the concept of fixed width integers is a C thing which > > + * does not apply to assembly code. > > + */ > > +#define GENMASK_U8(h, l) ((unsigned int)GENMASK_t(u8, h, l)) > > +#define GENMASK_U16(h, l) ((unsigned int)GENMASK_t(u16, h, l)) > > +#define GENMASK_U32(h, l) GENMASK_t(u32, h, l) > > +#define GENMASK_U64(h, l) GENMASK_t(u64, h, l) > > + > > +/* > > * __GENMASK_U128() depends on _BIT128() which would not work > > * in the asm code, as it shifts an 'unsigned __int128' data > > * type instead of direct representation of 128 bit constants > > > > -- > > 2.45.3 > >
