On Tue, Oct 02, 2018 at 09:42:48AM +0200, Rasmus Villemoes wrote:
> On 2018-10-02 03:13, William Breathitt Gray wrote:
> The cover letter says
>
> The clump_size argument can be an arbitrary number of bits and is not
> required to be a multiple of 2.
>
> by which I assume you mean "power of 2", but either way, the above code
> does not seem to take into account the case where bits_offset +
> clump_size straddles a word boundary, so it wouldn't work for a
> clump_size that does not divide BITS_PER_LONG.
E.g. 3 bits in a clump? Hmm...
Why would we need that? I mean some real use case?
> May I suggest another approach:
You may, of course, but see above and my comments below.
> unsigned long bitmap_get_value(const unsigned long *bitmap, unsigned
> start, unsigned width): Get the value of bitmap[start:start+width] for
> 1<=width<=BITS_PER_LONG (it's up to the caller to ensure this is within
> the defined region). That can almost be an inline
>
> bitmap_get_value(const unsigned long *bitmap, unsigned start, unsigned
> width)
> {
> unsigned idx = BIT_WORD(start);
> unsigned offset = start % BITS_PER_LONG;
> unsigned long lower = bitmap[idx] >> offset;
> unsigned long upper = offset <= BITS_PER_LONG - width ? 0 :
> bitmap[idx+1] << (BITS_PER_LONG - offset);
> return (lower | upper) & GENMASK(width-1, 0)
> }
>
> Then you can implement the for_each_set_clump by a (IMO) more readable
>
> for (i = 0, start = 0; i < num_ports; i++, start += gpio_reg_size) {
> word_mask = bitmap_get_value(mask, start, gpio_reg_size);
> if (!word_mask)
> continue;
> ...
> }
I would rather go with two prototypes to get()/set() a clump in the bitmap
in a way when it's aligned and BITS_PER_LONG % clump_size == 0.
unsigned long bitmap_get_clump(unsigned long *src, unsigned int start, unsigned int clump_size)
{
unsigned int index = BIT_WORD(start);
unsigned int offset = start % BITS_PER_LONG;
/* These just for spelling the restrictions */
WARN_ON(BITS_PER_LONG % clump_size);
WARN_ON(offset % clump_size);
/* TODO: take care of clump_size == 64 */
return (bitmap[index] >> offset) & GENMASK(clump_size - 1, 0);
}
Something similar with set with additional parameter unsigned long value
which has MSB cleared till we reach [clump_size - 1 : 0].
--
With Best Regards,
Andy Shevchenko
