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

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Date:	Mon, 7 May 2007 19:47:44 -0400
From:	"Mike Frysinger" <vapier.adi@...il.com>
To:	"David Brownell" <david-b@...bell.net>
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 4/25/07, David Brownell <david-b@...bell.net> wrote:
> On Wednesday 25 April 2007, Mike Frysinger wrote:
> > the spi_device structure has a bits_per_word so that you can change
> > the value on a per-device setting, yet the spi_board_info structure
> > does not ... this means that the bus-specific structure has to have a
> > bits_per_word member which the spi bus driver will copy into the spi
> > device bits_per_word member
>
> Actually that's more likely a driver-specific characteristic than
> something related to board wiring/configuration ... a characteristic
> of the particular protocol requests being made.  That's why for
> example bits_per_word has a per-transfer override, and drivers are
> able to call spi_setup(spi).

hmm, true ...

> > 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 ? :)

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 ...
-mike
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