linux-kernel - Re: [spi-devel-general] adding bits_per_word to struct spi_board_info to mirror struct spi

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Message-Id: <200705072153.46411.david-b@pacbell.net>
Date:	Mon, 7 May 2007 21:53:45 -0700
From:	David Brownell <david-b@...bell.net>
To:	"Mike Frysinger" <vapier.adi@...il.com>
Cc:	spi-devel-general@...ts.sourceforge.net,
	"Wu, Bryan" <Bryan.Wu@...log.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [spi-devel-general] adding bits_per_word to struct spi_board_info to mirror struct spi_device

On Monday 07 May 2007, Mike Frysinger wrote:
> On 4/25/07, David Brownell <david-b@...bell.net> wrote:
> > On Wednesday 25 April 2007, Mike Frysinger wrote:
> 
> > > is there something obvious i'm missing ?  seems to me that if the
> > > generic spi framework respects bits_per_word on a per-spi device
> > > basis, then it should be exposed in the generic info structure so that
> > > the setting can be tracked in the boards file ...
> >
> > The initial driver set didn't need it, that's all.  ISTR someone
> > else pointed out this quirk, but never provided a patch to resolve
> > the issue.
> 
> so which direction should it be ?  or should it be both ? :)

Add bits_per_word to spi_board_info, and have the device creation
logic copy it into spi_device as it's created.


> Blackfin at the moment is doing DMA/bits_per_word setup in the boards
> ... we could move these to the drivers and have each one just call
> spi_setup() at init, or i could post a patch for the common framework
> if you think that's an OK direction to [also] go ...

I don't see what you're getting at here.  The SPI core doesn't
do anything with DMA, beyond passing DMA addresses through when
necessary.  (Needed to handle messages derived from scatterlists,
since I don't want lower layers to know scatterlists, but otherwise
uncommon.)

And when each spi_device is created, the core calls spi_setup()
with the data.  That seems like the natural place to set up
things like DMA and so forth...

The pxa2xx_spi driver uses spi_board_info.controller_data to pass
dma setup/tuning data from board init logic.  

- Dave
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