| Message ID | 20240529045909.1796787-1-tong.ho@amd.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | qemu/bitops.h: Locate changed bits | expand |
On 5/29/2024 12:59, Tong Ho wrote:> Add inlined functions to obtain a mask of changed bits. 3 flavors > are added: toggled, changed to 1, changed to 0. > > These newly added utilities aid common device behaviors where > actions are taken only when a register's bit(s) are changed. > > Signed-off-by: Tong Ho <tong.ho@amd.com> > --- > include/qemu/bitops.h | 33 +++++++++++++++++++++++++++++++++ > 1 file changed, 33 insertions(+) > > diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h > index 2c0a2fe751..7a701474ea 100644 > --- a/include/qemu/bitops.h > +++ b/include/qemu/bitops.h > @@ -148,6 +148,39 @@ static inline int test_bit(long nr, const unsigned long *addr) > return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1))); > } > > +/** > + * find_bits_changed - Returns a mask of bits changed. > + * @ref_bits: the reference bits against which the test is made. > + * @chk_bits: the bits to be checked. > + */ > +static inline unsigned long find_bits_changed(unsigned long ref_bits, > + unsigned long chk_bits) > +{ > + return ref_bits ^ chk_bits; > +} > + > +/** > + * find_bits_to_1 - Returns a mask of bits changed from 0 to 1. > + * @ref_bits: the reference bits against which the test is made. > + * @chk_bits: the bits to be checked. > + */ > +static inline unsigned long find_bits_to_1(unsigned long ref_bits, > + unsigned long chk_bits) > +{ > + return find_bits_changed(ref_bits, chk_bits) & chk_bits; > +} > + > +/** > + * find_bits_to_0 - Returns a mask of bits changed from 1 to 0. > + * @ref_bits: the reference bits against which the test is made. > + * @chk_bits: the bits to be checked. > + */ > +static inline unsigned long find_bits_to_0(unsigned long ref_bits, > + unsigned long chk_bits) > +{ > + return find_bits_to_1(chk_bits, ref_bits); > +} > + > /** > * find_last_bit - find the last set bit in a memory region > * @addr: The address to start the search at Reviewed-by: Lei Wang <lei4.wang@intel.com>
On Wed, 29 May 2024 at 06:05, Tong Ho <tong.ho@amd.com> wrote: > > Add inlined functions to obtain a mask of changed bits. 3 flavors > are added: toggled, changed to 1, changed to 0. > > These newly added utilities aid common device behaviors where > actions are taken only when a register's bit(s) are changed. Generally we would expect this kind of "add new utility functions" patch to appear in a series together with some patches which actually use the new functions. Otherwise this is all dead code. More generally: * the other bit operations in this file work on bit arrays which are arbitrary-length arrays of unsigned long, so these new functions don't fit the pattern * we have the bitops functions partly because they're inherited from the Linux kernel. The use of unsigned long works quite badly in QEMU, because for us 'long' is a type that is almost always wrong. QEMU devices usually want a type of a known length, which is either 'uint32_t' or 'uint64_t'. So I'm dubious about adding more functions that work on unsigned long. thanks -- PMM
Point taken, and I am withdrawing this patch. I will post a new implementation following the arbitrary-length array pattern in a later date, and only as part of a series including the consuming code. Thanks, Tong Ho
diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h index 2c0a2fe751..7a701474ea 100644 --- a/include/qemu/bitops.h +++ b/include/qemu/bitops.h @@ -148,6 +148,39 @@ static inline int test_bit(long nr, const unsigned long *addr) return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1))); } +/** + * find_bits_changed - Returns a mask of bits changed. + * @ref_bits: the reference bits against which the test is made. + * @chk_bits: the bits to be checked. + */ +static inline unsigned long find_bits_changed(unsigned long ref_bits, + unsigned long chk_bits) +{ + return ref_bits ^ chk_bits; +} + +/** + * find_bits_to_1 - Returns a mask of bits changed from 0 to 1. + * @ref_bits: the reference bits against which the test is made. + * @chk_bits: the bits to be checked. + */ +static inline unsigned long find_bits_to_1(unsigned long ref_bits, + unsigned long chk_bits) +{ + return find_bits_changed(ref_bits, chk_bits) & chk_bits; +} + +/** + * find_bits_to_0 - Returns a mask of bits changed from 1 to 0. + * @ref_bits: the reference bits against which the test is made. + * @chk_bits: the bits to be checked. + */ +static inline unsigned long find_bits_to_0(unsigned long ref_bits, + unsigned long chk_bits) +{ + return find_bits_to_1(chk_bits, ref_bits); +} + /** * find_last_bit - find the last set bit in a memory region * @addr: The address to start the search at
Add inlined functions to obtain a mask of changed bits. 3 flavors are added: toggled, changed to 1, changed to 0. These newly added utilities aid common device behaviors where actions are taken only when a register's bit(s) are changed. Signed-off-by: Tong Ho <tong.ho@amd.com> --- include/qemu/bitops.h | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+)