On Thu, 5 Sep 2024 15:40:11 -0500 David Lechner <dlechner@xxxxxxxxxxxx> wrote: > On 9/5/24 10:17 AM, Angelo Dureghello wrote: > > ... One reply to a comment David made. Jonathan > > > + */ > > + if (st->single_channel) > > + clk_rate = DIV_ROUND_CLOSEST(clk_rate, 4); > > + else > > + clk_rate = DIV_ROUND_CLOSEST(clk_rate, 8); > > + > > Having the sample rate depend on how many channels are enabled in > the buffer seems a bit odd. Sampling frequency is not strictly > defined in IIO, so I think it would be fine to always return the > same value no matter how many channels are enabled. > > We will just need to document that the sampling frequency is the > rate per sample, not per channel. So if two channels are enabled, > the effective sampling rate per channel is 1/2 of the sampling > rate reported by the sysfs attribute. There is an oddity around this that we've never cleared up fully. In my head at least if there is a single sampling_frequency it applies to 'scans', not individual channel reads (so would change with the number of channels enabled). If there is a per channel attribute we do have documentation: What: /sys/bus/iio/devices/iio:deviceX/in_voltageX_sampling_frequency What: /sys/bus/iio/devices/iio:deviceX/in_powerY_sampling_frequency What: /sys/bus/iio/devices/iio:deviceX/in_currentZ_sampling_frequency KernelVersion: 5.20 Contact: linux-iio@xxxxxxxxxxxxxxx Description: Some devices have separate controls of sampling frequency for individual channels. If multiple channels are enabled in a scan, then the sampling_frequency of the scan may be computed from the per channel sampling frequencies. For many devices the sampling frequency isn't down to each sample taking N microsecs and them running back to back, it is instead a function of a periodic sampling start for samples that take the same time whatever the sampling frequency. Also for simultaneous sampling ADCs it is never channel dependent. So I think if you want to avoid the confusion, make your device fall into the description above and provide a per channel attribute rather than shared_by_all. Or keep it as things stand and have it halve when you double the channels. > > > + *val = clk_rate; > > + > > + return IIO_VAL_INT; > > + } ...
