Re: [PATCH] dmaengine: stm32-mdma: avoid 64-bit division

[Arnd Bergmann]

On Wed, Oct 11, 2017 at 4:27 PM, Benjamin Gaignard
<benjamin.gaignard@xxxxxxxxxx> wrote:
> 2017-10-11 16:01 GMT+02:00 Arnd Bergmann <arnd@xxxxxxxx>:
>
>> @@ -398,6 +400,9 @@ static enum dma_slave_buswidth stm32_mdma_get_max_width(u32 buf_len, u32 tlen)
>>                         break;
>>         }
>>
>> +       if (addr % max_width)
>> +               max_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
>> +
>
> I'm only half-convince by the implicite 32 bits cast done into
> function prototype.
> If we keep using dma_addr_t and use do_div() instead of %
> does compiler can still optimize the code ?
>

I wouldn't want to add a do_div() here, since it's guaranteed
not to be needed. Would you prefer an explicit cast here
and leave the argument as dma_addr_t?

We could also use a bit mask here like

  if (addr & (max_width-1))

or we could combined it with the check above:

                if ((((buf_len | addr) & (max_width - 1)) == 0) &&
                   (tlen >= max_width))

       Arnd