On 07/02/2013 05:21 PM, Lars-Peter Clausen wrote: > On 07/02/2013 04:55 PM, Hector Palacios wrote: >> Hello, >> >> On 07/02/2013 03:28 PM, Alexandre Belloni wrote: >>> On 02/07/2013 14:58, Lars-Peter Clausen wrote: >>>> On 07/02/2013 12:49 PM, Hector Palacios wrote: >>>>> Greetings, >>>>> >>>>> The mxs-lradc has some hardware specific features like the DIVIDE_BY_TWO (an >>>>> analog divide by two circuit that can be activated per channel). >>>>> This is not currently implemented in the driver and I was wondering what would >>>>> be the way to expose and control such setting. A specific sysfs entry? Somehow >>>>> through the device tree? >>>>> >>>>> Is there any example of how to control a hw-specific feature in other similar >>>>> iio drivers? >>>>> >>>> >>>> This sounds as if the channel scale is programmable. There are quite a few >>>> drivers for devices which have similar features, just make the scale property >>>> writable and provide a scale_available. >>>> >>> >>> I was looking at that yesterday as I had to had a scale for the >>> temperature sensors. You'll have to be careful because the maximum >>> measured voltage when DIVIDE_BY_TWO is not set is 1.85V and when it is >>> set, it becomes VDDIO - 50mv. > > I had a quick peak at the datasheet and I think that's a typo. VDDIO is 3.3V. > This sentence also doesn't make much sense if divide by two would actually > lower the range. "For input channels (other than BATT, 5V, or VDDIO) with > signals larger than 1.85 V, the divide-by-two option should be set." Uhm, ignore this, parse error on my side. I thought the dash was a hyphen not a minus. > >>> >>> Also, scaling for quite a lot of channels is fixed. You'll also get >>> channels with a fixed divider that can take DIVIDE_BY_TWO. That is quite >>> a mess ;) >> >> Thank you, I checked and it's easy to add custom sysfs attributes using >> IIO_DEVICE_ATTR(). I was thinking whether adding a divide_by_two attribute per >> channel: >> >> divide_by_two0 >> divide_by_two1 >> ... >> divide_by_two7 >> >> or a unique divide_by_two descriptor that admits a mask value for all channels. >> I think the first approach (one per channel) is cleaner. Opinions? > > Just use the scale attribute for this. That's the standard way to handle this, > don't invent custom interfaces if there is already a generic one. > > - Lars > -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
