linux-kernel - Re: [PATCH 1/3] spi: Add helper functions for setting up transfers

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Message-ID: <50EDD96A.5080900@metafoo.de>
Date:	Wed, 09 Jan 2013 21:56:10 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Jonathan Cameron <jic23@...nel.org>
CC:	Grant Likely <grant.likely@...retlab.ca>,
	Julia Lawall <Julia.Lawall@...6.fr>,
	spi-devel-general@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, Jonathan Cameron <jic23@....ac.uk>,
	linux-iio@...r.kernel.org
Subject: Re: [PATCH 1/3] spi: Add helper functions for setting up transfers

On 01/09/2013 08:20 PM, Jonathan Cameron wrote:
> On 01/09/2013 05:31 PM, Lars-Peter Clausen wrote:
>> Quite often the pattern used for setting up and transferring a synchronous SPI
>> transaction looks very much like the following:
>>
>> 	struct spi_message msg;
>> 	struct spi_transfer xfers[] = {
>> 		...
>> 	};
>>
>> 	spi_message_init(&msg);
>> 	spi_message_add_tail(&xfers[0], &msg);
>> 	...
>> 	spi_message_add_tail(&xfers[ARRAY_SIZE(xfers) - 1], &msg);
>>
>> 	ret = spi_sync(&msg);
>>
>> This patch adds two new helper functions for handling this case. The first
>> helper function spi_message_init_with_transfers() takes a spi_message and an
>> array of spi_transfers. It will initialize the message and then call
>> spi_message_add_tail() for each transfer in the array. E.g. the following
>>
>> 	spi_message_init(&msg);
>> 	spi_message_add_tail(&xfers[0], &msg);
>> 	...
>> 	spi_message_add_tail(&xfers[ARRAY_SIZE(xfers) - 1], &msg);
>>
>> can be rewritten as
>>
>> 	spi_message_init_with_transfers(&msg, xfers, ARRAY_SIZE(xfers));
>>
>> The second function spi_sync_transfer() takes a SPI device and an array of
>> spi_transfers. It will allocate a new spi_message (on the stack) and add all
>> transfers in the array to the message. Finally it will call spi_sync() on the
>> message.
>>
>> E.g. the follwing
>>
>> 	struct spi_message msg;
>> 	struct spi_transfer xfers[] = {
>> 		...
>> 	};
>>
>> 	spi_message_init(&msg);
>> 	spi_message_add_tail(&xfers[0], &msg);
>> 	...
>> 	spi_message_add_tail(&xfers[ARRAY_SIZE(xfers) - 1], &msg);
>>
>> 	ret = spi_sync(spi, &msg);
>>
>> can be rewritten as
>>
>> 	struct spi_transfer xfers[] = {
>> 		...
>> 	};
>>
>> 	ret = spi_sync_transfer(spi, xfers, ARRAY_SIZE(xfers));
>>
>> The patch also adds a new cocci script which can detect such sequences as
>> described above and transform them automatically to use the new helper
>> functions.
>>
>> Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>
>>
> Principle looks good to me and some nice little duplication removal
> savings.
> 
> My coccinelle isn't really up to checking that, but for the functions
> Acked-by: Jonathan Cameron <jic23@...nel.org>
> 
> When all comments are in on the code we'll have to think about how to
> merge this.  If you have much else planned that will hit those iio drivers
> then things will get uggly unless it goes through that tree.
> 
> Guess it all depends on whether others like the patch though ;)

The IIO patches can easily wait another release until the spi has made it's way
up into mainline. I just didn't want to send out the helper functions without
any realworld examples on how they can be used.

- Lars

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