Re: [PATCH V3 1/2] MIPS: Remove irqflags.h dependency from bitops.h

[David Daney <ddaney.cavm@gmail.com>]

On 09/03/2012 02:52 PM, Jim Quinlan wrote:
> The "else clause" of most functions in bitops.h invoked
> raw_local_irq_{save,restore}() and so had a dependency on irqflags.h.  This
> fix moves said code to bitops.c, removing the dependency.
>
> Signed-off-by: Jim Quinlan <jim2101024@gmail.com>


This is much better I think.

Now only a few very minor things I would change...

> ---
>   arch/mips/include/asm/bitops.h |  114 +++++++------------------
>   arch/mips/include/asm/io.h     |    1 +
>   arch/mips/lib/Makefile         |    2 +-
>   arch/mips/lib/bitops.c         |  180 ++++++++++++++++++++++++++++++++++++++++
>   4 files changed, 214 insertions(+), 83 deletions(-)
>   create mode 100644 arch/mips/lib/bitops.c
>
> diff --git a/arch/mips/include/asm/bitops.h b/arch/mips/include/asm/bitops.h
> index 82ad35c..9fd0b1d 100644
> --- a/arch/mips/include/asm/bitops.h
> +++ b/arch/mips/include/asm/bitops.h
> @@ -14,7 +14,6 @@
>   #endif
>
>   #include <linux/compiler.h>
> -#include <linux/irqflags.h>
>   #include <linux/types.h>
>   #include <asm/barrier.h>
>   #include <asm/byteorder.h>		/* sigh ... */
> @@ -44,6 +43,24 @@
>   #define smp_mb__before_clear_bit()	smp_mb__before_llsc()
>   #define smp_mb__after_clear_bit()	smp_llsc_mb()
>
> +
> +/*
> + * These are the "slower" versions of the functions and are in bitops.c.
> + * These functions call raw_local_irq_{save,restore}().
> + */
> +extern void atomic_set_bit(unsigned long nr, volatile unsigned long *addr);
> +extern void atomic_clear_bit(unsigned long nr, volatile unsigned long *addr);
> +extern void atomic_change_bit(unsigned long nr, volatile unsigned long *addr);
> +extern int atomic_test_and_set_bit(unsigned long nr,
> +				   volatile unsigned long *addr);
> +extern int atomic_test_and_set_bit_lock(unsigned long nr,
> +					volatile unsigned long *addr);
> +extern int atomic_test_and_clear_bit(unsigned long nr,
> +				     volatile unsigned long *addr);
> +extern int atomic_test_and_change_bit(unsigned long nr,
> +				      volatile unsigned long *addr);
> +

No 'extern' needed.

These shouldn't be directly called from user code.  I would suggest 
renaming the functions to something like:

__mips_set_bit();


[...]
> diff --git a/arch/mips/lib/bitops.c b/arch/mips/lib/bitops.c
> new file mode 100644
> index 0000000..6562ab2
> --- /dev/null
> +++ b/arch/mips/lib/bitops.c
> @@ -0,0 +1,180 @@
> +
> +/*
> + * This file is subject to the terms and conditions of the GNU General Public
> + * License.  See the file "COPYING" in the main directory of this archive
> + * for more details.
> + *
> + * Copyright (c) 1994-1997, 99, 2000, 06, 07 Ralf Baechle (ralf@linux-mips.org)
> + * Copyright (c) 1999, 2000  Silicon Graphics, Inc.
> + */
> +
> +#include <linux/irqflags.h>
> +
> +#if _MIPS_SZLONG == 32
> +#define SZLONG_LOG 5
> +#define SZLONG_MASK 31UL
> +#elif _MIPS_SZLONG == 64
> +#define SZLONG_MASK 63UL
> +#define SZLONG_LOG 6
> +#endif
> +

There has to be a cleaner way to do this...  Perhaps:



#define SZLONG_LOG (ilog2(sizeof(unsigned long)) + 3)
#define SZLONG_MASK ((1 << SZLONG_LOG) - 1)

> +
> +/*
> + * atomic_set_bit - Atomically set a bit in memory.  This is called by
> + * if set_bit() if it cannot find a faster solution.
> + * @nr: the bit to set
> + * @addr: the address to start counting from
> + */
> +void atomic_set_bit(unsigned long nr, volatile unsigned long *addr)
> +{
> +	volatile unsigned long *a = addr;
> +	unsigned short bit = nr & SZLONG_MASK;

just make bit type 'int'.  In some cases forcing a narrower type than 
necessary requires the compiler to emit extra code.  I am not sure if it 
would here, but why use a type other than int unless absolutely necessary?

> +	unsigned long mask;
> +	unsigned long flags;
> +
> +	a += nr >> SZLONG_LOG;
> +	mask = 1UL << bit;
> +	raw_local_irq_save(flags);
> +	*a |= mask;
> +	raw_local_irq_restore(flags);
> +}

All these must be EXPORT_SYMBOL(), so the bitop intrinsics can be used 
from modules.