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:
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.
Joel
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