linux-kernel - Re: [PATCH] BMP085 : Change the macro to swap

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Date:	Thu, 24 Jun 2010 13:52:51 +0100
From:	Jonathan Cameron <kernel@...23.retrosnub.co.uk>
To:	"Datta, Shubhrajyoti" <shubhrajyoti@...com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Christoph Mair <christoph.mair@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] BMP085  : Change the macro to swap

On 06/24/10 13:41, Datta, Shubhrajyoti wrote:
> 
> Changing the macro to swap the bytes as the reason that the first byte is the MSB and the next is LSB.
Are you sure on this one?

The swap would be right if you were using an i2c function that is aware that it is
reading word data (16bit).

Here it just thinks it is reading a string of bytes.  Hence the bytes will indeed
come out big endian.  So if you have a big endian machine this patch will swap the
bytes round incorrectly.

Of course I might just be half asleep today ;)
> 
> Signed-off-by: Shubhrajyoti D <shubhrajyoti@...com>
> ---
>  drivers/misc/bmp085.c |   41 +++++++++++++++++++++++++++++------------
>  1 files changed, 29 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/misc/bmp085.c b/drivers/misc/bmp085.c
> index 8af6f1b..74c5b12 100644
> --- a/drivers/misc/bmp085.c
> +++ b/drivers/misc/bmp085.c
> @@ -79,18 +79,35 @@ static s32 bmp085_read_calibration_data(struct i2c_client *client)
>  
>  	if (status != BMP085_CALIBRATION_DATA_LENGTH*sizeof(u16))
>  		return -EIO;
> -
> -	cali->AC1 =  be16_to_cpu(tmp[0]);
> -	cali->AC2 =  be16_to_cpu(tmp[1]);
> -	cali->AC3 =  be16_to_cpu(tmp[2]);
> -	cali->AC4 =  be16_to_cpu(tmp[3]);
> -	cali->AC5 =  be16_to_cpu(tmp[4]);
> -	cali->AC6 = be16_to_cpu(tmp[5]);
> -	cali->B1 = be16_to_cpu(tmp[6]);
> -	cali->B2 = be16_to_cpu(tmp[7]);
> -	cali->MB = be16_to_cpu(tmp[8]);
> -	cali->MC = be16_to_cpu(tmp[9]);
> -	cali->MD = be16_to_cpu(tmp[10]);
> +/*
> + * From the datasheet
> + *
> + * BMP085 Reg Addr
> + * parameter	|	MSB	|	LSB
> + * AC1		|	0xAA	|	0xAB
> + * AC2		|	0xAC	|	0xAD
> + * AC3		|	0xAE	|	0xAF
> + * AC4		|	0xB0	|	0xB1
> + * AC5		|	0xB2	|	0xB3
> + * AC6		|	0xB4	|	0xB5
> + * B1		|	0xB6	|	0xB7
> + * B2		|	0xB8	|	0xB9
> + * MB		|	0xBA	|	0xBB
> + * MC		|	0xBC	|	0xBD
> + * MC		|	0xBE	|	0xBF
> + *
> + */
> +	cali->AC1 =  swab16(tmp[0]);
> +	cali->AC2 =  swab16(tmp[1]);
> +	cali->AC3 =  swab16(tmp[2]);
> +	cali->AC4 =  swab16(tmp[3]);
> +	cali->AC5 =  swab16(tmp[4]);
> +	cali->AC6 = swab16(tmp[5]);
> +	cali->B1 = swab16(tmp[6]);
> +	cali->B2 = swab16(tmp[7]);
> +	cali->MB = swab16(tmp[8]);
> +	cali->MC = swab16(tmp[9]);
> +	cali->MD = swab16(tmp[10]);
>  	return 0;
>  }
>  

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