linux-kernel - Re: [PATCH] [drivers] [SPI] SPI_GPIO: add support for controllers with missing MISO pin

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Message-Id: <200906250836.53027.david-b@pacbell.net>
Date:	Thu, 25 Jun 2009 08:36:52 -0700
From:	David Brownell <david-b@...bell.net>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	"'LKML'" <linux-kernel@...r.kernel.org>,
	spi-devel-general@...ts.sourceforge.net, kyungmin.park@...sung.com
Subject: Re: [PATCH] [drivers] [SPI] SPI_GPIO: add support for controllers with missing MISO pin

On Thursday 25 June 2009, Marek Szyprowski wrote:
> > Thing is, this raises two related issues:  (a) there's the
> > analagous input-only case where MOSI isn't used, e.g. for
> > some kinds of sensor; and (b) there's also "real 3-wire SPI"
> > (spi->mode & SPI_3WIRE) where interactions are limited to
> > half duplex and one pin switches roles between MOSI and MISO.
> > 
> > Clearly this "output-only" case is a subset of SPI_3WIRE (the
> > MOMI/SISO pin can't switch direction) so one more change I
> > want to see is requiring that spi->mode flag be set in all
> > SPI devices registered when this mode is used.

Don't forget that change ...

 
> > If you have time, it would be good to generalize this patch
> > to cover all of those 3-wire modes ... accept all half
> > duplex calls, use gpio_direction_*() to switch direction.
> >
> > If not -- e.g. nothing to test that with! -- then I can
> > understand, but please make your changes with that model
> > in mind, and leave an appropriate FIXME in place.
> 
> I'm sorry, but I have only a hw board with missing MISO pin so I won't
> be able to properly check/debug any other configurations.

OK, then just stick to what you can test, and comment the issue.


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