linux-kernel - Re: [PATCH v2 2/4] iio: adc: add support for Allwinner SoCs ADC

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Message-ID: <a3928a7a-b600-27b8-a038-dc5e0c8a7a99@kernel.org>
Date:	Sat, 23 Jul 2016 08:37:47 +0200
From:	Jonathan Cameron <jic23@...nel.org>
To:	Quentin Schulz <quentin.schulz@...e-electrons.com>,
	jdelvare@...e.com, linux@...ck-us.net, knaack.h@....de,
	lars@...afoo.de, pmeerw@...erw.net,
	maxime.ripard@...e-electrons.com, wens@...e.org,
	lee.jones@...aro.org
Cc:	linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org,
	linux-iio@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	thomas.petazzoni@...e-electrons.com,
	antoine.tenart@...e-electrons.com
Subject: Re: [PATCH v2 2/4] iio: adc: add support for Allwinner SoCs ADC

On 21/07/16 14:15, Quentin Schulz wrote:
> On 20/07/2016 16:57, Jonathan Cameron wrote:
>> On 19/07/16 09:33, Quentin Schulz wrote:
>>> On 18/07/2016 15:18, Jonathan Cameron wrote:
>>>> On 15/07/16 10:59, Quentin Schulz wrote:
> [...]
>>>>> +	enable_irq(info->temp_data_irq);
>>>> Is this hardware spitting out extra irqs?  If not, much better to just
>>>> leave it enabled all the time and control whether it can occur or not
>>>> by controlling the device state..
>>>
>>> The temp_data_irq occurs every SUNXI_GPADC_TEMP_PERIOD(x) periods (in
>>> the current state of the driver: 2s). What do you mean by controlling
>>> the device state? Enabling or disabling the hardware part of the IP
>>> responsible of getting the temperature
>>> (SUNXI_GPADC_TP_TPR_TEMP_ENABLE(x) here)?
>> Yes, or something along those lines if it wakes up fast enough.
> 
> The ADC wakes up fast enough but resets its internal time clock (I don't
> know if it's the right term to use). Note that the temperature interrupt
> occurs by period of X seconds in this IP.
> 
> This means that each time we disable the ADC on the hardware side, no
> temperature interrupt will occur within the first X seconds. I don't
> think this is what we want.
I'm guessing X is non trivial ;)

So fair enough.  Could you add this justification as a comment in the
driver somewhere so that people coming back to this in a few years time
will know what the justification for this 'unusual' handling is.

Thanks,

Jonathan
> 
> [...]
> 
> Quentin
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