linux-kernel - Re: [PATCH] ad7877: fix spi word size to 16 bit

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Date:	Sat, 15 May 2010 20:15:24 +0200
From:	Oskar Schirmer <os@...ix.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Mike Frysinger <vapier.adi@...il.com>,
	Daniel Glöckner <dg@...ix.com>,
	Oskar Schirmer <os@...ix.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Oliver Schneidewind <osw@...ix.com>,
	Michael Hennerich <michael.hennerich@...log.com>
Subject: Re: [PATCH] ad7877: fix spi word size to 16 bit

On Thu, May 13, 2010 at 00:53:35 -0700, Dmitry Torokhov wrote:
> On Fri, May 07, 2010 at 02:23:07PM -0400, Mike Frysinger wrote:
> > On Fri, May 7, 2010 at 05:41, Daniel Glöckner wrote:
> > > On 05/06/2010 08:26 PM, Mike Frysinger wrote:
> > >> i think it'd be a better idea to do something like:
> > >>   if (spi->bits_per_word != 16) {
> > >>     if (spi->bits_per_word) {
> > >>       dev_err(&spi->dev, "Invalid SPI settings; bits_per_word must be 16\n");
> > >>       return -EINVAL;
> > >>     }
> > >>     spi->bits_per_word = 16;
> > >>     spi_setup(spi);
> > >>   }
> > >
> > > There is no way to set bits_per_word using struct spi_board_info. The
> > > description of that structure in spi.h explicitly lists the wordsize as
> > > one of the parameters drivers should set themself in probe().
> > >
> > > Only struct bfin5xx_spi_chip allows to set this value in the board code.
> > 
> > an obvious shortcoming in the SPI framework that should be fixed, but
> > that doesnt make any difference to the above code now does it ?  it'll
> > operate correctly regardless of the SPI bus master.
> 
> So is the updated patch coming?

The basic question I see is, whether it is in the
responsibility of ad7877 to check a wrong setting
possibly caused in board specific code. If so,
then the proposal by Mike should be used, but if not
so, it would introduce unneeded code.

Remember: both versions end up in correctly setting
bits_per_word, with the difference merely in feedback
level.

This is a design decision, I'ld say. So what are the
opinions on it, has it been taken yet, previously?

  Oskar
-- 
oskar schirmer, emlix gmbh, http://www.emlix.com
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