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

[Jonathan Cameron <jic23@kernel.org>]

On 10/24/13 16:17, Srinivas Pandruvada wrote:
> 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,
Sorry for not being clear, I simply meant the IIO_ROT bit was in the next batch,
but as it is connected to my comment here, didn't want to start another discussion
in reply to that patch.

(hence I never replied to that patch)
> 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
>>>
> 
> -- 
> To unsubscribe from this list: send the line "unsubscribe linux-iio" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html