From mboxrd@z Thu Jan 1 00:00:00 1970 From: quentin.schulz@free-electrons.com (Quentin Schulz) Date: Wed, 20 Jul 2016 14:37:40 +0200 Subject: [PATCH v2 2/4] iio: adc: add support for Allwinner SoCs ADC In-Reply-To: References: <1468576754-3273-1-git-send-email-quentin.schulz@free-electrons.com> <1468576754-3273-3-git-send-email-quentin.schulz@free-electrons.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 18/07/2016 15:18, Jonathan Cameron wrote: [...] >> + >> + if (!wait_for_completion_timeout(&info->completion, >> + msecs_to_jiffies(100))) { >> + ret = -ETIMEDOUT; >> + goto out; >> + } >> + >> + if (info->flags & SUNXI_GPADC_ARCH_SUN4I) >> + *val = info->temp_data * 133 - 257000; > Why report as processed? I'd just report them as raw with the scale > and offset provided. It's not a big thing, but if we can leave it so > that the conversion only occurs when desired, why not? > > For in kernel users, this all happen 'automagically' anyway ;) > Mmmmh, in the code above we apply the scale on the raw value and then the offset. While in iio_convert_raw_to_processed (http://lxr.free-electrons.com/source/drivers/iio/inkern.c#L507), the offset is applied before the scale. The way would be to factorize the computation by scale: Now: *val = raw * scale + offset Then: *val = (raw + offset/scale) * scale But the offset is an integer and offset/scale is therefore rounded. Currently, we have the following values: sun4i: -257000/133 = -1932.3308270676691 sun5i: -144700/100 = -1447 sun6i: -271000/167 = -1622.754491017964 Do we accept such rounding? If not, we either stay with the processed value in read_raw or patch inkern to add an offset to apply after having applied the scale to the raw value (val2 from iio_channel_read is yet unused with IIO_CHAN_INFO_OFFSET for example, we could use that to specify an offset2 to apply after the switch(scale_type)-case). [...] Quentin -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 819 bytes Desc: OpenPGP digital signature URL: