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

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Date:	Sun, 16 May 2010 15:25:34 -0400
From:	Mike Frysinger <vapier.adi@...il.com>
To:	Oskar Schirmer <os@...ix.com>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Daniel Glöckner <dg@...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 Sat, May 15, 2010 at 14:15, Oskar Schirmer wrote:
> 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.

imo, unsupported board settings should always be detected & rejected.
all SPI master drivers do this (detect & reject unsupported SPI slave
settings).
-mike
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