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SubjectRe: [PATCH] iio: mma8452: add power mode sysfs co nfiguration
Am 14.11.2017 05:56 schrieb harinath Nampally:
> Hi Martin,
>
>> But given your concerns, I would strip down this patch to only offer
>> the
>> already documented "low_noise" and "low_power" modes. It wouldn't be
>> worth it to extend the ABI just because of this!
> OK then we can map 'low_noise' to high resolution mode. But I am afraid
> I can't test the functionality because I don't have proper instruments
> to
> measure the current draw(in microAmps) accurately.
>
>> I would like "oversampling" more than this "power_mode" too. For this
>> driver it would be far more complicated to implement though. I doubt
>> that it'll be done. power_mode is basically already there implicitely,
>> and given that there *is* the ABI, we could offer it for free.
> I think 'oversampling' is already implemented, as I see
> 'case IIO_CHAN_INFO_OVERSAMPLING_RATIO:'
> being handled which is basically setting the all 4 different power
> modes.
> If we also add 'power_mode', I think it would be like having two
> different user interfaces for
> same functionality. So I don't see much of value adding 'power_mode' as
> well.
> Please correct me if I am wrong.
>
> Thanks,
> Harinath
>

You're right. I should've looked more closely. oversampling is there and
seems to
work. No need to blow up this driver or let alone extend an ABI now.
Let's drop
this patch.

thanks
martin


> On Sun, Nov 12, 2017 at 7:28 AM, Martin Kepplinger <martink@posteo.de>
> wrote:
>> On 2017-11-11 01:33, Jonathan Cameron wrote:
>>> On Mon, 6 Nov 2017 08:19:58 +0100
>>> Martin Kepplinger <martink@posteo.de> wrote:
>>>
>>>> This adds the power_mode sysfs interface to the device as documented
>>>> in
>>>> sysfs-bus-iio.
>>>>
>>>> ---
>>>>
>>>> Note that I explicitely don't sign off on this.
>>>>
>>>> This is a starting point for anybody who can test it and check for
>>>> correct
>>>> API usage, and ABI correctness, as documented in
>>>> Documentation/ABI/testing/sys-bus-iio
>>>> (grep it for "power_mode"). The ABI doc probably would need an
>>>> addition
>>>> too, if the 4 power modes here seem generally useful (there are only
>>>> 2 listed there)!
>>>>
>>>> So, if you can test this, feel free to set up a proper patch or
>>>> two, and I'm happy to review.
>>>>
>>>> Please note that this patch is quite old. It really should be that
>>>> simple
>>>> as far as my understanding back then. We always list the available
>>>> frequencies
>>>> of the given power mode we are in, for example, already, and
>>>> everything
>>>> basically is in place except for the user interface.
>>>
>>> Hmm. A lot of devices support something along these lines. The issue
>>> has always been - how is userspace to figure out what to do with it?
>>> It's all very vague...
>>>
>>> Funnily enough - this used to be really common, but is becoming less
>>> so
>>> now - presumably because no one was using it much (or maybe I am
>>> reading
>>> too much into that ;)
>>>
>>> Now the question is whether it can be tied to better defined things?
>>>
>>> Here low noise restricts the range to 4g. Issue is that we don't
>>> actually
>>> have writeable _available attributes (which correspond to range in
>>> this case).
>>>
>>
>> Does it? Isn't it merely less oversampling.
>>
>>> Low power mode... This one is apparently oversampling. If possible
>>> support
>>> it as that as we have well defined interfaces for that.
>>>
>>> Jonathan.
>>
>> Ah, I remember; the oversampling settings was actually a reason why I
>> hadn't submitted the patch :) The oversampling API would definitely be
>> more accurate.
>>
>> I would like "oversampling" more than this "power_mode" too. For this
>> driver it would be far more complicated to implement though. I doubt
>> that it'll be done. power_mode is basically already there implicitely,
>> and given that there *is* the ABI, we could offer it for free.
>>
>> But given your concerns, I would strip down this patch to only offer
>> the
>> already documented "low_noise" and "low_power" modes. It wouldn't be
>> worth it to extend the ABI just because of this!
>>
>> Users would have a simple switch if they don't really *want* to know
>> the
>> details. I think it can be useful to just say "I don't care about
>> power
>> consuption. Be as accurate as possible" or "I just want this think to
>> work. Use a little power as possible." Sure it's vage, but would it be
>> useless?

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