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

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Message-ID: <aec7e5c30911252350r717393e8sd476fa7e3aeb301f@mail.gmail.com>
Date:	Thu, 26 Nov 2009 16:50:46 +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()

On Thu, Nov 26, 2009 at 4:21 PM, Grant Likely <grant.likely@...retlab.ca> wrote:
> On Wed, Nov 25, 2009 at 11:47 PM, Magnus Damm <magnus.damm@...il.com> wrote:
>> 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.

Sure, I plan on posting a V2 of the MSIOF driver. I plan to keep the
dummy txrx_word() function for now - this to disconnect the cleanup
from the driver integration, hope that sounds like a good plan.

Cheers,

/ magnus
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