Re: [PATCH] spi: Allow using spi_bitbang_setup() with custom txrx_bufs()

[Magnus Damm <magnus.damm@gmail.com>]

On Thu, Nov 26, 2009 at 4:21 PM, Grant Likely <grant.likely@secretlab.ca> wrote:
> On Wed, Nov 25, 2009 at 11:47 PM, Magnus Damm <magnus.damm@gmail.com> wrote:
>> On Thu, Nov 26, 2009 at 7:15 AM, Grant Likely <grant.likely@secretlab.ca> wrote:
>>> On Wed, Nov 25, 2009 at 1:26 AM, Magnus Damm <magnus.damm@gmail.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