On Friday, November 07, 2014 at 02:34:31 AM, Huang Shijie wrote: > why change them to gpio? If we change them to gpio. Could the DMA still > works fine? > did you test the DMA with this patch? > > Add Marek for this patch too. I didn't look too deep into the patch, so here's just my experience: 1) The AUART block signals and GPIO block signals are not sychronised using the same clock. Therefore, the latency between toggling of the AUART lines and the GPIO-driven pins will not be deterministic and will vary. There might be a way to approximate that, but that's definitelly not a reliable solution. This is very bad for example if you drive RS485 DIR line with the RTS pin as a GPIO ; the RTS pin will toggle at non-deterministic time compared to the end of UART transmission. This will trigger bit-loss on the RS485 line and you just don't want that. 2) Speaking of RS485, there's [1] and [2]. which I believe apply to any combo of UART+GPIO toggling. So I hate to bring the bad news , but UART+GPIO combo toggling is really a bad bad idea. HTH [1] http://comments.gmane.org/gmane.linux.serial/6770 [2] http://article.gmane.org/gmane.linux.serial/3619/ Best regards, Marek Vasut -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
