From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jonathan Cameron Subject: Re: [PATCHv2 1/3] iio: Add Nuvoton NAU7802 ADC driver Date: Sun, 23 Jun 2013 18:33:10 +0100 Message-ID: <51C73156.7040807@kernel.org> 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> <51C6FE00.8010900@metafoo.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <51C6FE00.8010900-Qo5EllUWu/uELgA04lAiVw@public.gmane.org> Sender: linux-iio-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Lars-Peter Clausen Cc: Alexandre Belloni , Shawn Guo , Grant Likely , jimwall@q.com, brian-ZKiFAVwZFM2FeswfMrDH8w@public.gmane.org, Maxime Ripard , linux-iio-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org, Jonathan Cameron , Rob Landley , Rob Herring List-Id: devicetree@vger.kernel.org On 06/23/2013 02:54 PM, Lars-Peter Clausen wrote: > 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. > I agree entirely. We can always make it controllable later as long as we keep the default the same as the value you hard code in now.