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Subject: Re: [PATCH 9/9 v2] iio: pressure: bmp280: read calibration data once
To: Linus Walleij <linus.walleij@linaro.org>
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From: Jonathan Cameron <jic23@kernel.org>
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Date: Mon, 27 Jun 2016 19:59:15 +0100
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On 27/06/16 13:11, Linus Walleij wrote:
> On Sun, Jun 26, 2016 at 12:21 PM, Jonathan Cameron <jic23@kernel.org> wrote:
>> On 22/06/16 21:53, Linus Walleij wrote:
>>> The calibration data is described as coming from an E2PROM and that
>>> means it does not change. Just read it once at probe time and store
>>> it in the device state container. Also toss the calibration data
>>> into the entropy pool since it is device unique.
>>>
>>> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
>>
>> One nitpick inline, but it's minor enough I'm just being grumpy
>> about it so don't bother fixing it unless you want to.
>>
>> On the adding entropy bit, any idea who to sanity check that with?
>> It's not something we've done before, so I just want a bit of
>> reassurance ideally;)
> 
> I've done it in a few places whenever I ran into device-unique numbers,
> actually sensors often have device-unique calibration and are thus well
> suited to toss into the entropy pool.
> 
> The data from devices isn't really trusted to increase entropy: it may,
> but it's not relied on by the algorithm, just mixed in, see:
> http://lwn.net/Articles/507115/
Fair enough then.

J
> 
>>>       ret = regmap_bulk_read(data->regmap, BMP180_REG_CALIB_START, buf,
>>>                              sizeof(buf));
>>> -
>> Good but unrelated change.  Should have been in a different patch...
> 
> Dropped unrelated whitespace fix.
> 
> Yours,
> Linus Walleij
>