Hi Marek, On 03/07/2013 06:37, Marek Vasut wrote: > > I'm attaching a patch. Alex, please give it a go and see if it fixes your issue. > It is _VERY_ ugly. > Quite ugly ;) It indeed seems to fix the issue. > The basic idea behind the the patch is that, as (attempted to be) explained > above, subsequent writes to DATA register in PIO mode cause constant generation > of clock on the bus and therefore a very long transfer of zero data. This > confuses the I2C peripherals of course. > > The patch implements clock stretching for PIO writes (maybe we need this for > reads too) by making the controller blast out only 4 (or less) bytes of data in > each write into the DATA register. To prevent interruption of the transfer > between writes into the DATA register, the SCK is held low using the > RETAIN_CLOCK bit. > > But (!) here comes the caveat. The PIO was introduced to speed up small > transfers. Introducing clock stretching into PIO mode operation might completely > remove this advantage. This has to be measured again. > And now, PIO mode is slower than DMA... -- Alexandre Belloni, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
