[spi-devel-general] [PATCH v3 0/2] spi: driver for Cirrus EP93xx SPI controller

[Mika Westerberg]

On Mon, Apr 19, 2010 at 12:04:30PM -0500, H Hartley Sweeten wrote:
> On Friday, April 16, 2010 9:59 PM, Mika Westerberg wrote:
...
> > when it wants to assert/deassert the chip select. I don't see how this is
> > limited to built-in GPIOs only (maybe I'm missing something). Now it is in
> > responsibility of platform board files to allocate necessary chipselect lines,
> > and translate 'spi->chip_select' and 'value' to something meaningful.
> 
> The way you are currently handling the chip select limits you to the built-in
> GPIO's because the 'gpio_request' happens early in the platform init before any
> external gpio expanders might be available.
> 
> The best example is if your first SPI device is actually a GPIO expander that
> is chip selected by a built-in GPIO.  This GPIO expander is then used to provide
> the chip selects for additional SPI devices on the bus.

Ok.. got it. I didn't consider that one.

> >> Ryan and I worked out a runtime setup/cleanup for the spi device chip selects
> >> in the spi driver I have in my tree.  I will take a look at it and see how
> >> much trouble it will be to implement in your driver.
> >
> > Ok.
> 
> I have a patch almost working.
> 
> Have you had time to implement any of the changes that Grant Likely proposed?

Mostly yes. I'm still considering whether I should drop the polling mode.

> One of them dealt with the ep93xx_spi_{de}select_device functions.  Before I
> post my proposed changes I would like to make sure it is based on your most
> current code.

I changed chipselect functions to be something like (espi->cs_control is copied
from info structure):

        if (espi->cs_control)
                espi->cs_control(spi->chip_select, !!(spi->mode & SPI_CS_HIGH),
                                 espi->cs_data);

I'm not exactly sure whether this is what Grant meant, however.

> BTW, my patch will also handle Martin Guy's issue with using a null chip select.

Yeah. I also have that fixed.

Do you want me to send next revision so that you can base your proposed changes
on top of that or how to proceed?

> Actually, the chip-select isn't really null since the SFRMOUT line is still
> asserted (active-low) during any SPI transfer but the effect is still the same.

Too bad that SFRMOUT cannot be used as GPIO, we could then use it as proper
software controlled chipselect ;)

Thanks,
MW