On 11/09/2016 07:37 PM, Joel Holdsworth wrote: > On 09/11/16 05:01, Marek Vasut wrote: >> On 11/08/2016 06:30 PM, Joel Holdsworth wrote: >>>>>> On the whole, I don't think the zero-length transfers are too >>>>>> egregiously bad, and all the alternatives seem worse to me. >>>>> >>>>> So why not turn the CS line into GPIO and just toggle the GPIO? >>>> >>>> Does that work with *all* SPI controllers? >>>> >>> >>> It does not - no. See my other email. >> >> And is that line an actual CS of that lattice chip or a generic input >> which almost works like CS? >> > > I mean a generic output vs. a special CS output built into the SPI > master of the application processor. Take a look at how spi_set_cs(..) > works: No. I am asking whether the signal which is INPUT on the iCE40 side is really a chipselect signal for the SPI bus OR something which mostly behaves/looks like a chipselect but is not really a chipselect. > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/spi/spi.c?id=refs/tags/v4.9-rc4#n695 > > > static void spi_set_cs(struct spi_device *spi, bool enable) > { > if (spi->mode & SPI_CS_HIGH) > enable = !enable; > > if (gpio_is_valid(spi->cs_gpio)) > gpio_set_value(spi->cs_gpio, !enable); > else if (spi->master->set_cs) > spi->master->set_cs(spi, !enable); > } > > So on some SPI masters, spi->master->set_cs is handled separately from > normal GPIOs. Hence why I want to use this machinery, rather than doing > it with a GPIO. This is not relevant. FYI: using separate GPIO as a SPI chip select has it's own problems. -- 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
