From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lars-Peter Clausen Subject: Re: [PATCHv2 1/3] iio: Add Nuvoton NAU7802 ADC driver Date: Sun, 23 Jun 2013 15:54:08 +0200 Message-ID: <51C6FE00.8010900@metafoo.de> References: <1371754675-12242-1-git-send-email-alexandre.belloni@free-electrons.com> <1371754675-12242-2-git-send-email-alexandre.belloni@free-electrons.com> <51C590B5.2060308@kernel.org> <51C5923D.6030609@metafoo.de> <51C5A1AF.3070404@free-electrons.com> <51C5A499.5050509@metafoo.de> <51C5A68F.3000300@free-electrons.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <51C5A68F.3000300@free-electrons.com> Sender: linux-kernel-owner@vger.kernel.org To: Alexandre Belloni Cc: Jonathan Cameron , Shawn Guo , Grant Likely , jimwall@q.com, brian@crystalfontz.com, Maxime Ripard , linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, devicetree-discuss@lists.ozlabs.org, Jonathan Cameron , Rob Landley , Rob Herring List-Id: devicetree@vger.kernel.org On 06/22/2013 03:28 PM, Alexandre Belloni wrote: > On 22/06/2013 15:20, Lars-Peter Clausen wrote: >> On 06/22/2013 03:07 PM, Alexandre Belloni wrote: >>> On 22/06/2013 14:02, Lars-Peter Clausen wrote: >>>> On 06/22/2013 01:55 PM, Jonathan Cameron wrote: >>>>> On 06/20/2013 07:57 PM, Alexandre Belloni wrote: >>>>>> The Nuvoton NAU7802 ADC is a 24-bit 2-channels I2C ADC, with adjustable >>>>>> gain and sampling rates. >>>>>> >>>>> Sorry, somewhat low on time today so only a quick review. >>>>> >>>>> 1) Missing userspace ABI documentation. Also, perhaps min_conversions is >>>>> a little vague? Not that I have a better idea! >>>> I really don't like the name min_conversions either. Isn't this effectively >>>> a decimation filter? >>> Yeah, it could be seen like that but it is only relevant and only >>> happens when switching between channels. I'm open to any ideas. >>> >> I see. Is there anything about this in the datasheet on how many conversions >> you usually need? Is this really something you need to change at runtime or >> does moving this to platform data work? >> >> > > There is actually nothing in the datasheet. The default value (6 > conversions) was found experimentally. What I did was saturating the ADC > with the higher value on one channel and the lower value on the other > one and I tried to find when reading both channel sequentially was > resulting in a correct value. > > You may not need to change it at runtime. And that value mainly depend > on the precision versus speed balance you want to achieve. If you know > that the values on both channels will not be to far apart, then you may > not need to wait at all. > > Would you think that is something I should hide in the DT ? Or maybe I > can drop that knob for now and see if it is needed in the future. > It is always a good idea to be conservative when introducing new ABI, so if you think we can get away with hardcoding this in the driver I think that's a good idea. - Lars