linux-kernel - Re: [lm-sensors] [PATCH V1] fix adc to voltage calculation in da9052 power driver

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Message-ID: <20131219181049.GA6854@roeck-us.net>
Date:	Thu, 19 Dec 2013 10:10:49 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	Anthony Olech <anthony.olech.opensource@...semi.com>,
	lm-sensors@...sensors.org, Anton Vorontsov <anton@...msg.org>,
	David Woodhouse <dwmw2@...radead.org>,
	linux-kernel@...r.kernel.org,
	David Dajun Chen <david.chen@...semi.com>
Subject: Re: [lm-sensors] [PATCH V1] fix adc to voltage calculation in da9052
 power driver

On Thu, Dec 19, 2013 at 03:54:54PM +0100, Jean Delvare wrote:
> Hi Anthony,
> 
[ ... ]
> 
> BTW, you (and we) probably shouldn't waste too much energy on this.
> ADCs are only accurate to some degree anyway. If you take the
> components connected to the input into consideration, the accuracy gets
> even worse. For example, if the input voltage must be scaled down to
> fit in the ADC's range, you need at least one resistor, which in best
> cases will have a 1% accurate value (known as tolerance.) That's ten
> times the LSB of your 10-bit ADC, at which point / 1023 or / 1024
> really makes no practical difference. Sub-percent tolerant resistors are
> expensive and rare in consumer electronics in my experience.
> 
True, but on the other side (and after looking into the datasheet)
the driver already calculated the voltage on adc4..6 correctly,
so unless you disagree I would like to apply the hwmon patch to -next
for consistency.

Thanks,
Guenter
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