Re: [Uclinux-dist-devel] [PATCH 1/2] spi/bfin_spi: only request GPIO on first load

[Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>]

On Fri, Oct 22, 2010 at 02:41:12AM -0400, Mike Frysinger wrote:
> On Fri, Oct 22, 2010 at 02:30, Grant Likely wrote:
> > On Fri, Oct 22, 2010 at 02:01:47AM -0400, Mike Frysinger wrote:
> >> From: Michael Hennerich <michael.hennerich-OyLXuOCK7orQT0dZR+AlfA@public.gmane.org>
> >>
> >> The gpiolib code does not allow people to do gpio_request() on a GPIO
> >> once it has already been requested.  So make sure we only request the
> >> pin on the first setup of a SPI device.  Otherwise, if you attempts to
> >> reconfigure a SPI device on the fly (like change bit sizes), the setup
> >> function incorrectly fails.
> >
> > Doesn't that mean that the gpio pin be requested at device probe time
> > instead of in a function that can be repeatedly called?
> 
> not sure what you mean.  this is a pin specific to a spi slave device.
>  there is no "spi probe" function for spi slave devices, only the "spi
> setup" function.

The spi master device is responsible for managing its own cs lines,
and it should know what they are at bfin_spi_probe time.  Looking at
commit d3cc71f7 which reworked the cs_gpio bits, I see that the
blackfin driver places the gpio information with the slave instance.

One could be argue that the spi_slave can be considered the owner of
spi ss lines, but that runs counter to current conventions, and
counter to how I want to implement common infrastructure for handling
gpio slave select lines.

I see that this patch is a bug fix, and the driver already implements
bad behaviour, so I have little choice but to pick it up.  However, it
is only a band-aid solution and in the long term it should be
refactored to store the gpio slave-select lines with the spi_master
device (probably after some common gpio-slave-select infrastructure is
put in place).

g.

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