linux-kernel - Re: [PATCH] spi: Allow using spi_bitbang_setup() with custom txrx

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Date:	Thu, 26 Nov 2009 00:21:29 -0700
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Magnus Damm <magnus.damm@...il.com>
Cc:	spi-devel-general@...ts.sourceforge.net,
	dbrownell@...rs.sourceforge.net, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] spi: Allow using spi_bitbang_setup() with custom 
	txrx_bufs()

On Wed, Nov 25, 2009 at 11:47 PM, Magnus Damm <magnus.damm@...il.com> wrote:
> Hi Grant,
>
> On Thu, Nov 26, 2009 at 7:15 AM, Grant Likely <grant.likely@...retlab.ca> wrote:
>> On Wed, Nov 25, 2009 at 1:26 AM, Magnus Damm <magnus.damm@...il.com> wrote:
>>>        /* per-word shift register access, in hardware or bitbanging */
>>> -       cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)];
>>> -       if (!cs->txrx_word)
>>> -               return -EINVAL;
>>> +       if (bitbang->txrx_bufs == spi_bitbang_bufs) {
>>> +               cs->txrx_word = bitbang->txrx_word[spi->mode & mode_mask];
>>> +               if (!cs->txrx_word)
>>> +                       return -EINVAL;
>>> +       }
>>
>> Hmmm... this smells like an ugly hack to me.  It seems to me that if
>> some bitbang backend drivers don't want this code, then it should be
>> encoded into a callback so it can be overridden.  Thoughts.
>
> Yeah, it's far from clean. I want to make use of spi_bitbang_setup()
> in my MSIOF driver, but I want to avoid dummy txtx_word[] callbacks
> that will be unused since i'm using a driver specific
> bitbang->txrx_bufs function.
>
> I guess the attached patch is slightly cleaner? I like the idea of
> letting bitbang drivers use shared code for
> spi_bitbang_setup()/spi_bitbang_cleanup() with their private
> setup_transfer() function which in turn calls
> spi_bitbang_setup_transfer(). My impression is that there's quite a
> bit of duplicated setup()/cleanup() code.

This is certainly less ugly.  But with the points brought up in the
other thread, I want to have a close look at spi-bitbang before I
start applying stuff.  It seems nasty.  Give me a few days.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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