[PATCH 8/8] dmaengine/dw_dmac: Add support for DMA_SLAVE_CONFIG

[Linus Walleij]

On Mon, Jan 16, 2012 at 12:42 PM, Viresh Kumar <viresh.kumar at st.com> wrote:
> On 1/16/2012 3:20 PM, Viresh KUMAR wrote:
>> +     /*
>> +      * Fix sconfig's burst size according to dw_dmac. We need to convert
>> +      * them as: 1 -> 0, 2 -> 1, 4 -> 2, 8 -> 3, 16 -> 4.
>> +      *
>> +      * This can be done by findiding least significant bit set: n & (n - 1)
>> +      */
>> +     sconfig->src_maxburst &= sconfig->src_maxburst - 1;
>> +     sconfig->dst_maxburst &= sconfig->dst_maxburst - 1;
>
> Perhaps, this looks incorrect. It will always return 0. :(
> Can somebody suggest any inbuild function to do this, i think
>
> find_next_bit(sconfig->src_maxburst, sizeof(sconfig->src_maxburst), 0)
>
> will do it.

Are you looking for ffs() from <linus/bitops.h>?

find-first-set (the include boils down to include/asm-generic/bitops/ffs.h
if you want to check the implementation).

Linus Walleij