Re: [PATCH 7/9] iio: mma8452: change iio event type to IIO_EV_TYPE_MAG

[Martin Kepplinger <martink@posteo.de>]

Am 2015-07-07 um 09:05 schrieb Jonathan Cameron:
> 
> 
> On 6 July 2015 09:39:12 BST, Martin Fuzzey <mfuzzey@parkeon.com> wrote:
>> On 05/07/15 13:50, Jonathan Cameron wrote:
>>> On 04/07/15 14:55, Martin Kepplinger wrote:
>>>> IIO_EV_TYPE_THRESH in rising direction describes an event where the
>>>> threshold is crossed in rising direction, positive or negative
>> values
>>>> being possible. This is not the case here.
>>>>
>>>> Since the threshold is no signed value and only the magnitude is
>> compared,
>>>> IIO_EV_TYPE_MAG is what describes the behaviour of these devices,
>> see the
>>>> sysfs-bus-iio ABI Documentation.
>>
>> Fwiw there was some discussion of this before the initial submission:
>>
>> http://www.spinics.net/lists/linux-iio/msg14039.html
>>
>> Initially I used a magnitude too but Jonathan convinced me it should be
>>
>> a threshold.
>>
>> "
>>
>> The  moment you know the sign of the magnitude it stops being a
>> magnitude
>> and becomes a generic threshold.  Report it as such and control it as
>> such.
>>
>> "
>>
>> Thing is that the hardware indeed only compares the absolute value for 
>> the threshold *but* indicates with the event the sign.
>> However it is true that the driver doesn't currently do anything with 
>> the sign information.
> Ah. That explains the confusion.
> This is a common enough case. 
> Usual approach is the slightly hacky option of having two threshold events. Setting limit on either effects both.
> Enabling either effects both (or you can eat the wrong one in driver if you prefer
>  when only one is enabled)

I tried to implement THRESH somehow but it gets too messy. Yes, what you
*can* read for an event is positive or negative acceleration value (g,
whatever). But, say, positive g doesn't at all indicate THRESH RISING .
It could be negative g in freefall mode on one axis, and so on...

So the sign of the current value doesn't help you turning MAG into
TRESH. Really I think, MAG is what describes these devices.

>>
>>
>>>> Signed-off-by: Martin Kepplinger
>> <martin.kepplinger@theobroma-systems.com>
>>>> Signed-off-by: Christoph Muellner
>> <christoph.muellner@theobroma-systems.com>
>>> This is a fix and so should have been the first patch in the series. 
>> It will
>>> want to go via a different tree (iio-fixes) and probably be marked
>> for stable.
>>>
>>> I would however like Peter's ack on this as well before taking it.
>>>> ---
>>>>   drivers/iio/accel/mma8452.c | 10 +++++-----
>>>>   1 file changed, 5 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/drivers/iio/accel/mma8452.c
>> b/drivers/iio/accel/mma8452.c
>>>> index 7f6e3b4..e23ebd0 100644
>>>> --- a/drivers/iio/accel/mma8452.c
>>>> +++ b/drivers/iio/accel/mma8452.c
>>>> @@ -598,21 +598,21 @@ static void mma8452_transient_interrupt(struct
>> iio_dev *indio_dev)
>>>>   	if (src & data->chip_info->ev_src_xe)
>>>>   		iio_push_event(indio_dev,
>>>>   			       IIO_MOD_EVENT_CODE(IIO_ACCEL, 0, IIO_MOD_X,
>>>> -						  IIO_EV_TYPE_THRESH,
>>>> +						  IIO_EV_TYPE_MAG,
>>>>   						  IIO_EV_DIR_RISING),
>>>>   			       ts);
>>>>   
>>>>   	if (src & data->chip_info->ev_src_ye)
>>>>   		iio_push_event(indio_dev,
>>>>   			       IIO_MOD_EVENT_CODE(IIO_ACCEL, 0, IIO_MOD_Y,
>>>> -						  IIO_EV_TYPE_THRESH,
>>>> +						  IIO_EV_TYPE_MAG,
>>>>   						  IIO_EV_DIR_RISING),
>>>>   			       ts);
>>>>   
>>>>   	if (src & data->chip_info->ev_src_ze)
>>>>   		iio_push_event(indio_dev,
>>>>   			       IIO_MOD_EVENT_CODE(IIO_ACCEL, 0, IIO_MOD_Z,
>>>> -						  IIO_EV_TYPE_THRESH,
>>>> +						  IIO_EV_TYPE_MAG,
>>>>   						  IIO_EV_DIR_RISING),
>>>>   			       ts);
>>>>   }
>>>> @@ -689,7 +689,7 @@ static int mma8452_reg_access_dbg(struct iio_dev
>> *indio_dev,
>>>>   
>>>>   static const struct iio_event_spec mma8452_transient_event[] = {
>>>>   	{
>>>> -		.type = IIO_EV_TYPE_THRESH,
>>>> +		.type = IIO_EV_TYPE_MAG,
>>>>   		.dir = IIO_EV_DIR_RISING,
>>>>   		.mask_separate = BIT(IIO_EV_INFO_ENABLE),
>>>>   		.mask_shared_by_type = BIT(IIO_EV_INFO_VALUE) |
>>>> @@ -700,7 +700,7 @@ static const struct iio_event_spec
>> mma8452_transient_event[] = {
>>>>   
>>>>   static const struct iio_event_spec mma8452_motion_event[] = {
>>>>   	{
>>>> -		.type = IIO_EV_TYPE_THRESH,
>>>> +		.type = IIO_EV_TYPE_MAG,
>>>>   		.dir = IIO_EV_DIR_RISING,
>>>>   		.mask_separate = BIT(IIO_EV_INFO_ENABLE),
>>>>   		.mask_shared_by_type = BIT(IIO_EV_INFO_VALUE) |
>>>>
>>
>> --
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>