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: <1178596106.5222.3.camel@roc-desktop>
Date:	Tue, 08 May 2007 11:48:26 +0800
From:	Bryan WU <bryan.wu@...log.com>
To:	David Brownell <david-b@...bell.net>,
	Mike Frysinger <vapier.adi@...il.com>
Cc:	spi-devel-general@...ts.sourceforge.net,
	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 Mon, 2007-05-07 at 19:47 -0400, Mike Frysinger wrote:
> 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

Yes, it is very common for spi_framework. DMA setting as well as
bits_per_word setup should be imported to spi_board_info struct. And
currently, there are some duplicated data members in spi_device struct
spi_board_info struct. This two structs are confused driver writers and
boards driver users.

Thanks
-Bryan Wu
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