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

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Message-ID: <aec7e5c30911252247i344f5bf3pb0240b9c23878bf5@mail.gmail.com>
Date:	Thu, 26 Nov 2009 15:47:17 +0900
From:	Magnus Damm <magnus.damm@...il.com>
To:	Grant Likely <grant.likely@...retlab.ca>
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()

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:
>> This patch modifies the shared spi bitbanging code
>> to allow using spi_bitbang_setup() even though the
>> txrx_word[] callbacks are unset. Useful for drivers
>> that want to make use of spi_bitbang_setup() but
>> have their own txrx_bufs() callback.

>> @@ -196,9 +205,11 @@ int spi_bitbang_setup(struct spi_device
>>        }
>>
>>        /* 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.

/ magnus

Download attachment "linux-2.6.33-pre-spi-word-mode-setup-20091126.patch" of type "application/octet-stream" (3503 bytes)