On 29 August 2018 at 19:33, Jan Kundrát <jan.kundrat@xxxxxxxxx> wrote: > On čtvrtek 16. srpna 2018 14:54:49 CEST, Baolin Wang wrote: >> >> + * @word_delay: clock cycles to inter word delay after each word size >> + * (set by bits_per_word) transmission. > > > I need a similar functionality for talking to a SPI device from userspace > -- see my attempt for implementing this in spi-orion.c at [1]. The device's > datasheet says that I should wait, e.g., 3µs between each two words. I > therefore like this patch :). > > The description can be improved because it left me wondering what "clock > this is about. I suppose it's about the SPI clock cycles and not CPU clock > cycles, right? I'll be hapy to patch this once Baolin confirms that that is > the intended meaning. Sorry for confusing. Since our SPI word delay unit is clock cycle of the SPI clock, so my intention of the word_delay's unit is SPI clock cycles according to our previous discussion. > > It seems that this is only implemented in one newly added driver. I'm > interested in supporting this in spi-orion.c, but that sounds like > driver-specific work for something which is pretty generic. How should this > be implemented? Given that drivers for SPI masters can implement a function > which transfers several words at once, there are not that many better > possibilities than adding udelay()s, though. Thoughts? > > What is your plan to do with drivers which do not implement this (yet)? If a > spi_transfer gets queued which asks for a word_delay delay, it is silently > ignored now, AFAIU. > > What about userspace support, spidev and spi_ioc_transfer (that's my target, > actually)? Is it OK to s/pad/word_delay/ in the spidev code and pass that to > the generated struct spi_transfer? In my opinion, once we support specifying > this from userspace, one has to definitely check that the SPI controller is > ready to honor this request. Do we want a new bit in spi_controller.flags > for this? > > With kind regards, > Jan > > [1] https://patchwork.kernel.org/patch/10221397/ -- Baolin Wang Best Regards
