On Wednesday, July 22, 2015 at 09:30:54 AM, Michal Suchanek wrote: > On 22 July 2015 at 06:49, Vinod Koul <vinod.koul@xxxxxxxxx> wrote: > > On Tue, Jul 21, 2015 at 10:14:11AM +0200, Michal Suchanek wrote: > >> > Or alternatively we could publish the limitations of the channel using > >> > capabilities so SPI knows I have a dmaengine channel and it can > >> > transfer max N length transfers so would be able to break rather than > >> > guessing it or coding in DT. Yes it may come from DT but that should > >> > be dmaengine driver rather than client driver :) > >> > > >> > This can be done by dma_get_slave_caps(chan, &caps) > >> > > >> > And we add max_length as one more parameter to existing set > >> > > >> > Also all this could be handled in generic SPI-dmaengine layer so that > >> > individual drivers don't have to code it in > >> > > >> > Let me know if this idea is okay, I can push the dmaengine bits... > >> > >> It would be ok if there was a fixed limit. However, the limit depends > >> on SPI slave settings. Presumably for other buses using the dmaengine > >> the limit would depend on the bus or slave settings as well. I do not > >> see a sane way of passing this all the way to the dmaengine driver. > > > > I don't see why this should be client (SPI) dependent. The max length > > supported is a dmaengine constraint, typically flowing from max > > blocks/length it can transfer. Know this limit can allow clients to split > > transfers. > > In practice on the board I have the maximum transfer length before it > fails depends on SPI bus speed which is set up per slave. I did not > try searching the space of possible settings thorougly and settled for > a setting that gives reasonable speed and transfer length. This looks more like a signal integrity issue though. > However, if this was not tied to the particular slave setting picked > in the current DT a formula would be needed that translates arbitrary > client settings to transfer size limit and there would be need to > somehow get the client settings to the formula in the dmaengine > driver. > > Thanks > > Michal Best regards, Marek Vasut -- 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
