On 10/11/2017 05:13 PM, Arnd Bergmann wrote: > On Wed, Oct 11, 2017 at 4:46 PM, Benjamin Gaignard > <benjamin.gaignard@xxxxxxxxxx> wrote: >> 2017-10-11 16:39 GMT+02:00 Arnd Bergmann <arnd@xxxxxxxx>: >>> 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)) >> >> That sound better for me since it doesn't limit the code to 32 bits architecture > > FWIW, I used the u32 type here because that's the limit of the > dma driver, the dma_addr_t gets converted to that anyway > later. > >>> >>> or we could combined it with the check above: >>> >>> if ((((buf_len | addr) & (max_width - 1)) == 0) && >>> (tlen >= max_width)) >> >> No it is more simple to read with two checks > > I should have mentioned that this variant would also change > behavior: the current code falls back to byte access when > the address alignment is less than the length alignment. > The change I suggested here would change that to use > the maximum possible address width that fits the alignment > of either size or address. Both alignment are required on address and length. The main advantage result is maximized in term of width. As for now I don't see any drawback except a short explanation. Nonetheless I need to think a little bit more about this change. > > I don't know what behavior we actually want though, or > if that change would be correct. > > Arnd > Regards Py -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
