linux-kernel - Re: [PATCH 02/19] staging: iio: isl29028: remove enable flag from isl29028_enable

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Message-ID: <6188afbc-08a8-a6b3-c1f1-68b414bb450a@kernel.org>
Date:   Sun, 15 Jan 2017 14:33:12 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Brian Masney <masneyb@...tation.org>
Cc:     linux-iio@...r.kernel.org, gregkh@...uxfoundation.org,
        devel@...verdev.osuosl.org, knaack.h@....de, lars@...afoo.de,
        pmeerw@...erw.net, linux-kernel@...r.kernel.org,
        ldewangan@...dia.com
Subject: Re: [PATCH 02/19] staging: iio: isl29028: remove enable flag from
 isl29028_enable_proximity()

On 14/01/17 20:00, Brian Masney wrote:
> On Sun, Dec 04, 2016 at 11:16:04AM +0000, Jonathan Cameron wrote:
>> On 04/12/16 02:19, Brian Masney wrote:
>>> isl29028_enable_proximity() has a boolean argument named enable. This
>>> function is only called once and the enable flag is set to true in that
>>> call. This patch removes the enable parameter from that function.
>>>
>>> Signed-off-by: Brian Masney <masneyb@...tation.org>
>>
>> The first thing that strikes me about this, is why do we have an enable
>> only function?
>>
>> I think the intention was probably that we also disable the proximity
>> sensing after the
>> reading was done...  Ideally we'd do this a little more cleverly,
>> perhaps using runtime
>> pm so that if someone is requesting a stream of proximity measurements,
>> we won't end up
>> powering up and down each time.
>>
>> It's a little 'interesting' as we would want to power this element down
>> even if we do
>> have a continuous stream of reads on the ALS.  As such we may need to
>> roll our own
>> equivalent of runtime pm.
>>
>> In the first instance, I'd just put a disable after the reading is
>> taken.  This will
>> make a bit of a mockery of the faster sampling frequencies but there we
>> are!
>>
>> ---------------------
>>
>> On second thoughts (stupid email is hiding somewhere to be sent when I
>> have wifi so can't reply to it) perhaps this is a coarse way of only
>> turning proximity on if the LED is present?  Not sure...
> 
> Hi Jonathan,
> 
> I chained your two replies together above. I am probably stating the
> obvious here, but I've verified with an oscilloscope that the IRDR pin
> that drives the external LED is off when the chip is first initialized
> and ALS readings are taken. The IRDR pin fluctuates between high and low
> every 100us (if memory serves me right) once the first proximity reading
> is taken until the chip is suspended.
> 
> What do you think about enabling runtime auto suspend after say 2
> seconds for the whole device? There is the situation that you describe
> where if someone is continuously polling the ALS but asks for a single
> proximity reading. The external LED will stay on in that case. Once the
> chip is suspended, and later resumes, the IRDR pin that drives the
> external LED will be off until the user asks for another proximity
> reading. That would allow for the faster sampling frequency.
> 
> If you still prefer, I'll go the route of shutting down the IRDR pin
> after a proximity reading is taken.
Perhaps runtime auto suspend for the whole thing is the simplest option.
I don't mind that much either way.

Jonathan
> 
> Brian
>