linux-kernel - Re: [PATCH V2] spi: remove check for bits_per

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Date:	Thu, 20 Dec 2012 11:33:47 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Grant Likely <grant.likely@...retlab.ca>
CC:	"broonie@...nsource.wolfsonmicro.com" 
	<broonie@...nsource.wolfsonmicro.com>,
	"ben-linux@...ff.org" <ben-linux@...ff.org>,
	"kgene.kim@...sung.com" <kgene.kim@...sung.com>,
	"baohua.song@....com" <baohua.song@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"spi-devel-general@...ts.sourceforge.net" 
	<spi-devel-general@...ts.sourceforge.net>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"jonas.gorski@...il.com" <jonas.gorski@...il.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH V2] spi: remove check for bits_per_word on transfer from
 low level driver

On Wednesday 19 December 2012 09:54 PM, Grant Likely wrote:
> On Tue, 18 Dec 2012 14:25:43 +0530, Laxman Dewangan<ldewangan@...dia.com>  wrote:
>> The spi core make sure that each transfer structure have the proper
>> setting for bits_per_word before calling low level transfer APIs.
>>
>> Hence it is no more require to check again in low level driver for
>> this field whether this is set correct or not. Removing such code
>> from low level driver.
>>
>> Signed-off-by: Laxman Dewangan<ldewangan@...dia.com>
> [...]
>> */
>>
>>   		if (prev_speed_hz != speed_hz
>> @@ -316,9 +315,8 @@ static int txx9spi_transfer(struct spi_device *spi, struct spi_message *m)
>>   	/* check each transfer's parameters */
>>   	list_for_each_entry (t,&m->transfers, transfer_list) {
>>   		u32 speed_hz = t->speed_hz ? : spi->max_speed_hz;
>> -		u8 bits_per_word = t->bits_per_word ? : spi->bits_per_word;
>> +		u8 bits_per_word = t->bits_per_word;
>>
>> -		bits_per_word = bits_per_word ? : 8;
> Have you verified here that bits_per_word can never be '0' here? What is
> the path that ensures spi->bits_per_word (and hence t->bits_per_word) is
> set to 8 here?
>
> Otherwise the patch looks good. Thanks for doing this work.


When we do the spi_add_device(), the spi_setup() get called.
In spi_setup, it make  sure that spi->bits_per_word is not zero.

in spi_setup(spi.c)

if (!spi->bits_per_word)
                 spi->bits_per_word = 8;


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