On 8/29/23 8:59 AM, Jan Beulich wrote:
> On 23.08.2023 22:07, Shawn Anastasio wrote:
>> Implement bitops.h, based on Linux's implementation as of commit
>> 5321d1b1afb9a17302c6cec79f0cbf823eb0d3fc. Though it is based off of
>> Linux's implementation, this code diverges significantly in a number of
>> ways:
>> - Bitmap entries changed to 32-bit words to match X86 and Arm on Xen
>> - PPC32-specific code paths dropped
>> - Formatting completely re-done to more closely line up with Xen.
>> Including 4 space indentation.
>
> With this goal, ...
>
>> --- a/xen/arch/ppc/include/asm/bitops.h
>> +++ b/xen/arch/ppc/include/asm/bitops.h
>> @@ -1,9 +1,335 @@
>> +/* SPDX-License-Identifier: GPL-2.0-or-later */
>> +/*
>> + * Adapted from Linux's arch/powerpc/include/asm/bitops.h.
>> + *
>> + * Merged version by David Gibson <da...@gibson.dropbear.id.au>.
>> + * Based on ppc64 versions by: Dave Engebretsen, Todd Inglett, Don
>> + * Reed, Pat McCarthy, Peter Bergner, Anton Blanchard. They
>> + * originally took it from the ppc32 code.
>> + */
>> #ifndef _ASM_PPC_BITOPS_H
>> #define _ASM_PPC_BITOPS_H
>>
>> +#include <asm/memory.h>
>> +
>> +#define __set_bit(n,p) set_bit(n,p)
>> +#define __clear_bit(n,p) clear_bit(n,p)
>
> ... you want to add blanks after the commas as well. (You might also
> simply omit parameters altogether.)
>
>> +#define BITOP_BITS_PER_WORD 32
>> +#define BITOP_MASK(nr) (1UL << ((nr) % BITOP_BITS_PER_WORD))
>> +#define BITOP_WORD(nr) ((nr) / BITOP_BITS_PER_WORD)
>> +#define BITS_PER_BYTE 8
>> +
>> /* PPC bit number conversion */
>> -#define PPC_BITLSHIFT(be) (BITS_PER_LONG - 1 - (be))
>> -#define PPC_BIT(bit) (1UL << PPC_BITLSHIFT(bit))
>> -#define PPC_BITMASK(bs, be) ((PPC_BIT(bs) - PPC_BIT(be)) | PPC_BIT(bs))
>> +#define PPC_BITLSHIFT(be) (BITS_PER_LONG - 1 - (be))
>> +#define PPC_BIT(bit) (1UL << PPC_BITLSHIFT(bit))
>> +#define PPC_BITMASK(bs, be) ((PPC_BIT(bs) - PPC_BIT(be)) | PPC_BIT(bs))
>> +
>> +/* Macro for generating the ***_bits() functions */
>> +#define DEFINE_BITOP(fn, op, prefix)
>> \
>> +static inline void fn(unsigned long mask,
>> \
>> + volatile unsigned int *_p)
>> \
>
> Nit: Style. Either
>
> static inline void fn(unsigned long mask,
> \
> volatile unsigned int *_p)
> \
>
> or
>
> static inline void fn(unsigned long mask,
> \
> volatile unsigned int *_p)
> \
>
> . Also there's again an underscore-prefixed identifier here.
>
Will fix both.
>> +{
>> \
>> + unsigned long old;
>> \
>> + unsigned int *p = (unsigned int *)_p;
>> \
>> + asm volatile (
>> \
>> + prefix
>> \
>> +"1: lwarx %0,0,%3,0\n"
>> \
>> + #op "%I2 %0,%0,%2\n"
>> \
>> + "stwcx. %0,0,%3\n"
>> \
>> + "bne- 1b\n"
>> \
>> + : "=&r" (old), "+m" (*p)
>> \
>> + : "rK" (mask), "r" (p)
>> \
>> + : "cc", "memory");
>> \
>
> The asm() body wants indenting by another four blanks (more instances below).
>
If I were to match the style used in the previous patch's atomic.h, the
body should be indented to line up with the opening ( of the asm
statement, right? I'll go ahead and do that for consistency's sake
unless you think it would be better to just leave it as-is with an extra
4 spaces of indentation.
>> +}
>> +
>> +DEFINE_BITOP(set_bits, or, "")
>> +DEFINE_BITOP(change_bits, xor, "")
>> +
>> +#define DEFINE_CLROP(fn, prefix)
>> \
>> +static inline void fn(unsigned long mask, volatile unsigned int *_p)
>> \
>> +{
>> \
>> + unsigned long old;
>> \
>> + unsigned int *p = (unsigned int *)_p;
>> \
>> + asm volatile (
>> \
>> + prefix
>> \
>> +"1: lwarx %0,0,%3,0\n"
>> \
>> + "andc %0,%0,%2\n"
>> \
>> + "stwcx. %0,0,%3\n"
>> \
>> + "bne- 1b\n"
>> \
>> + : "=&r" (old), "+m" (*p)
>> \
>> + : "r" (mask), "r" (p)
>> \
>> + : "cc", "memory");
>> \
>> +}
>> +
>> +DEFINE_CLROP(clear_bits, "")
>> +
>> +static inline void set_bit(int nr, volatile void *addr)
>> +{
>> + set_bits(BITOP_MASK(nr), (volatile unsigned int *)addr +
>> BITOP_WORD(nr));
>> +}
>> +static inline void clear_bit(int nr, volatile void *addr)
>> +{
>> + clear_bits(BITOP_MASK(nr), (volatile unsigned int *)addr +
>> BITOP_WORD(nr));
>> +}
>> +
>> +/**
>> + * test_bit - Determine whether a bit is set
>> + * @nr: bit number to test
>> + * @addr: Address to start counting from
>> + */
>> +static inline int test_bit(int nr, const volatile void *addr)
>> +{
>> + const volatile unsigned long *p = (const volatile unsigned long
>> *)addr;
>> + return 1UL & (p[BITOP_WORD(nr)] >> (nr & (BITOP_BITS_PER_WORD-1)));
>
> Nit: Too deep indentation. Plus blanks around - please. I also don't see
> the need for the UL suffix, when the function returns int only (and really
> means to return bool, I assume, but int is in line with x86 and Arm, I
> expect).
>
Will fix the indentation and spacing around -. I'll also drop the UL
suffix, but will keep the int return type, since as you guessed it's
what Arm/x86 do.
>> +}
>> +
>> +static inline unsigned long test_and_clear_bits(unsigned long mask,
>> volatile void *_p)
>> +{
>> + unsigned long old, t;
>> + unsigned int *p = (unsigned int *)_p;
>> +
>> + asm volatile (
>> + PPC_ATOMIC_ENTRY_BARRIER
>> + "1: lwarx %0,0,%3,0\n"
>> + "andc %1,%0,%2\n"
>> + "stwcx. %1,0,%3\n"
>> + "bne- 1b\n"
>> + PPC_ATOMIC_EXIT_BARRIER
>> + : "=&r" (old), "=&r" (t)
>> + : "r" (mask), "r" (p)
>> + : "cc", "memory");
>> +
>> + return (old & mask);
>> +}
>> +
>> +static inline int test_and_clear_bit(unsigned int nr,
>> + volatile void *addr)
>
> Nit: Too deep indentation again.
>
Will fix this and all subsequent occurrences.
>> +DEFINE_TESTOP(test_and_set_bits, or, 0)
>> +
>> +static inline int test_and_set_bit(unsigned long nr, volatile void *addr)
>> +{
>> + return test_and_set_bits(BITOP_MASK(nr), (volatile unsigned int *)addr
>> + BITOP_WORD(nr)) != 0;
>
> Too long line.
>
Will fix.
>> +}
>> +
>> +/**
>> + * __test_and_set_bit - Set a bit and return its old value
>> + * @nr: Bit to set
>> + * @addr: Address to count from
>> + *
>> + * This operation is non-atomic and can be reordered.
>> + * If two examples of this operation race, one can appear to succeed
>> + * but actually fail. You must protect multiple accesses with a lock.
>> + */
>> +static inline int __test_and_set_bit(int nr, volatile void *addr)
>> +{
>> + unsigned int mask = BITOP_MASK(nr);
>> + volatile unsigned int *p =
>> + ((volatile unsigned int *)addr) + BITOP_WORD(nr);
>> + unsigned int old = *p;
>> +
>> + *p = old | mask;
>> + return (old & mask) != 0;
>> +}
>> +
>> +/**
>> + * __test_and_clear_bit - Clear a bit and return its old value
>> + * @nr: Bit to clear
>> + * @addr: Address to count from
>> + *
>> + * This operation is non-atomic and can be reordered.
>> + * If two examples of this operation race, one can appear to succeed
>> + * but actually fail. You must protect multiple accesses with a lock.
>> + */
>> +static inline int __test_and_clear_bit(int nr, volatile void *addr)
>> +{
>> + unsigned int mask = BITOP_MASK(nr);
>> + volatile unsigned int *p =
>> + ((volatile unsigned int *)addr) + BITOP_WORD(nr);
>> + unsigned int old = *p;
>> +
>> + *p = old & ~mask;
>> + return (old & mask) != 0;
>> +}
>> +
>> +#define flsl(x) generic_flsl(x)
>> +#define fls(x) generic_fls(x)
>> +#define ffs(x) ({ unsigned int __t = (x); fls(__t & -__t); })
>> +#define ffsl(x) ({ unsigned long __t = (x); flsl(__t & -__t); })
>
> Hmm, here you even have two underscores as prefixes.
>
Another carryover from Arm, sorry. Will fix.
>> +/* Based on linux/include/asm-generic/bitops/ffz.h */
>> +/*
>> + * ffz - find first zero in word.
>> + * @word: The word to search
>> + *
>> + * Undefined if no zero exists, so code should check against ~0UL first.
>> + */
>> +#define ffz(x) __ffs(~(x))
>> +
>> +/**
>> + * hweightN - returns the hamming weight of a N-bit word
>> + * @x: the word to weigh
>> + *
>> + * The Hamming Weight of a number is the total number of bits set in it.
>> + */
>> +#define hweight64(x) generic_hweight64(x)
>> +#define hweight32(x) generic_hweight32(x)
>> +#define hweight16(x) generic_hweight16(x)
>> +#define hweight8(x) generic_hweight8(x)
>
> Not using popcnt{b,w,d}, e.g. via a compiler builtin?
>
Excellent point. It looks like gcc's __builtin_popcount* family of
builtins will do what we want here. I suppose the other architectures in
Xen don't do this because they target toolchains old enough to not have
these builtins?
>> +/* Based on linux/include/asm-generic/bitops/builtin-__ffs.h */
>> +/**
>> + * __ffs - find first bit in word.
>> + * @word: The word to search
>> + *
>> + * Undefined if no bit exists, so code should check against 0 first.
>> + */
>> +static /*__*/always_inline unsigned long __ffs(unsigned long word)
>
> What's this odd comment about here?
>
(Yet another) carryover from Arm. Will fix.
>> +{
>> + return __builtin_ctzl(word);
>> +}
>> +
>> +/**
>> + * find_first_set_bit - find the first set bit in @word
>> + * @word: the word to search
>> + *
>> + * Returns the bit-number of the first set bit (first bit being 0).
>> + * The input must *not* be zero.
>> + */
>> +#define find_first_set_bit(x) ({ ffsl(x) - 1; })
>
> Simply
>
> #define find_first_set_bit(x) (ffsl(x) - 1)
>
> without use of any extensions?
>
Good point, the extension usage here is obviously unnecessary. Will
drop.
>> +/*
>> + * Find the first set bit in a memory region.
>> + */
>> +static inline unsigned long find_first_bit(const unsigned long *addr,
>> + unsigned long size)
>> +{
>> + const unsigned long *p = addr;
>> + unsigned long result = 0;
>> + unsigned long tmp;
>> +
>> + while (size & ~(BITS_PER_LONG-1)) {
>> + if ((tmp = *(p++)))
>> + goto found;
>> + result += BITS_PER_LONG;
>> + size -= BITS_PER_LONG;
>> + }
>> + if (!size)
>> + return result;
>
> Just using 4-blank indentation isn't enough to make this Xen style.
> (More such elsewhere.)
>
Yes, fair enough. I'll reformat it.
>> + tmp = (*p) & (~0UL >> (BITS_PER_LONG - size));
>> + if (tmp == 0UL) /* Are any bits set? */
>> + return result + size; /* Nope. */
>> +found:
>
> Labels indented by at least one blank please. (More elsewhere.)
I wasn't aware of this style convention -- so a single blank before the
label would be correct? I'll add that in, then.
> Jan
Thanks,
Shawn
