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." >> >> 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
