[PATCH] spi: Set cs-gpios to output direction

On 05/24/14 04:54, Mark Brown wrote:

On Fri, May 23, 2014 at 05:57:34PM -0700, Stephen Boyd wrote:

quoted

Some gpios used for cs-gpios may not be configured for output by
default. In these cases gpio_set_value() won't have any effect
and so the chip select line won't toggle. Request the cs-gpios
and set them to output direction once we know if the chip select
is default high or default low.

Currently the SPI framework is expecting that the controller driver will
own the GPIOs so it's not requesting them at all - starting to request
them in the core without warning is likely to lead to double requests
which doesn't seem like the best idea ever.  The driver has to
understand that there are GPIO chip selects since it needs to figure out
what to do with any underlying hardware chip selects that it can't stop
toggling (there may be none or it may be directable into space with
pinmux but we can't rely on that).  

Ok. My SPI controller is relying on the pinctrl framework to request
these gpios and I didn't have that configured in DT.

quoted

I wonder if we should request the gpios when the master controller
probes or when a spi device is added? We only know what the default
value should be when the spi device is added. On the other hand,
we should probably fail probe if the gpio controller isn't ready when
the spi master controller probes.

Right, plus the fact that each driver has to open code the requesting,
probe deferral handling and so on.  It's not super awesome, the whole
area around GPIO chip select handling needs a bit of a sorched earth
refactoring.

Ideally we'd be able to error out only the device using an individual
GPIO rather than the whole controller if a GPIO isn't there for some
reason so doing it at device time would be nicer but my recollection is
that this won't play nicely with deferred probe, it's a while since I
looked so I may be misremembering.

Yes. There would need to be some hook into the SPI core from the driver
core that notified of any new driver probes. Then we could try and get
any pending cs-gpios again and then add the device that uses that chip
select.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by The Linux Foundation