Re: [PATCH v2 8/9] iio: Add channel modifiers for Quaternion Rotations

[Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>]

Hi Jonathan,
On 10/24/2013 04:18 AM, Jonathan Cameron wrote:
> On 10/23/13 20:11, Srinivas Pandruvada wrote:
>> A quaternion is composed of four components: a vector with x, y, z
>> coordinates and a w rotation. Added channel modifiers for exporting
>> these four components via user space.
>>
>> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> Quaternions are one of the 'interesting' cases that make me wonder if we need
> a slightly more generic form of read_raw.  The quaternion only has meaning
> with an associated scale.  Hence you really have to guarantee that you can grab all
> 4 components together.
>
> Do we need to rethink how the read callback works?
>
> Mind you, if we do that then we need to extend the description of the buffer element
> in the scan_mask.  We could define a compound description for a channel, but that is 'interesting'.
>
> I also don't like this being defined as type IIO_ROT - the units (such as exist are different).
> See next patch for what I'm referring to here.
I didn't receive your next patch with comments. Can you please resend?
Thanks,
Srinivas
> I've cc'd a few people who might have views on this.
>
>
>
>> ---
>>   drivers/iio/industrialio-core.c | 4 ++++
>>   include/linux/iio/types.h       | 4 ++++
>>   2 files changed, 8 insertions(+)
>>
>> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
>> index f95c697..4ffaead 100644
>> --- a/drivers/iio/industrialio-core.c
>> +++ b/drivers/iio/industrialio-core.c
>> @@ -80,6 +80,10 @@ static const char * const iio_modifier_names[] = {
>>   	[IIO_MOD_LIGHT_RED] = "red",
>>   	[IIO_MOD_LIGHT_GREEN] = "green",
>>   	[IIO_MOD_LIGHT_BLUE] = "blue",
>> +	[IIO_MOD_QUATERNION_X] = "quat_x",
>> +	[IIO_MOD_QUATERNION_Y] = "quat_y",
>> +	[IIO_MOD_QUATERNION_Z] = "quat_z",
>> +	[IIO_MOD_QUATERNION_W] = "quat_w",
>>   };
>>   
>>   /* relies on pairs of these shared then separate */
>> diff --git a/include/linux/iio/types.h b/include/linux/iio/types.h
>> index 88bf0f0..ac2345c 100644
>> --- a/include/linux/iio/types.h
>> +++ b/include/linux/iio/types.h
>> @@ -52,6 +52,10 @@ enum iio_modifier {
>>   	IIO_MOD_LIGHT_RED,
>>   	IIO_MOD_LIGHT_GREEN,
>>   	IIO_MOD_LIGHT_BLUE,
>> +	IIO_MOD_QUATERNION_X,
>> +	IIO_MOD_QUATERNION_Y,
>> +	IIO_MOD_QUATERNION_Z,
>> +	IIO_MOD_QUATERNION_W,
>>   };
>>   
>>   #define IIO_VAL_INT 1
>>