On Mon, 24 Jul 2017 10:16:00 +0200 Fabrice Gasnier <[email protected]> wrote:
> On 07/23/2017 01:00 PM, Jonathan Cameron wrote: > > On Tue, 18 Jul 2017 14:35:32 +0200 > > Fabrice Gasnier <[email protected]> wrote: > > > >> STM32 ADC allows each channel to be sampled with a different sampling time, > >> by setting SMPR registers. Basically, value depends on local electrical > >> properties. Selecting correct value for sampling time highly depends on > >> analog source impedance. There is a manual that may help in this process: > >> 'How to get the best ADC accuracy in STM32...' > >> > >> This patch allows to configure min-sample-time via device tree, either for: > >> - all channels at once: > >> min-sample-time = <10000>; /* nanosecs */ > >> > >> - independently for each channel (must match "st,adc-channels" list): > >> st,adc-channels = <0 1>; > >> min-sample-time = <5000 10000>; /* nanosecs */ > >> > >> Signed-off-by: Fabrice Gasnier <[email protected]> > > > > On question inline which may well just be down to me missing what > > happens when you query index element 2 from a 1 element device tree > > array. > > Hi Jonathan, > > I should probably comment on it, please see inline. > <snip> > >> } > >> @@ -1538,8 +1651,8 @@ static int stm32_adc_chan_of_init(struct iio_dev > >> *indio_dev) > >> struct property *prop; > >> const __be32 *cur; > >> struct iio_chan_spec *channels; > >> - int scan_index = 0, num_channels; > >> - u32 val; > >> + int scan_index = 0, num_channels, ret; > >> + u32 val, smp = 0; > >> > >> num_channels = of_property_count_u32_elems(node, "st,adc-channels"); > >> if (num_channels < 0 || > >> @@ -1548,6 +1661,13 @@ static int stm32_adc_chan_of_init(struct iio_dev > >> *indio_dev) > >> return num_channels < 0 ? num_channels : -EINVAL; > >> } > >> > >> + /* Optional sample time is provided either for each, or all channels */ > >> + ret = of_property_count_u32_elems(node, "min-sample-time"); > >> + if (ret > 1 && ret != num_channels) { > >> + dev_err(&indio_dev->dev, "Invalid min-sample-time\n"); > >> + return -EINVAL; > >> + } > >> + > >> channels = devm_kcalloc(&indio_dev->dev, num_channels, > >> sizeof(struct iio_chan_spec), GFP_KERNEL); > >> if (!channels) > >> @@ -1558,9 +1678,13 @@ static int stm32_adc_chan_of_init(struct iio_dev > >> *indio_dev) > >> dev_err(&indio_dev->dev, "Invalid channel %d\n", val); > >> return -EINVAL; > >> } > >> + > >> + of_property_read_u32_index(node, "min-sample-time", scan_index, > >> + &smp); > >> + > > I might be missing something, but doesn't this fail for the single shared > > value case? > > Yes, this fails in the single shared value case, with index >= 1. > Rewinding... when index is 0, it picks up 1st (shared) value. > Then fails for other index values. > > of_property_read_u32_index() documentation states out value remains > untouched in case of error: > /** > * of_property_read_u32_index... > [...] > * The out_value is modified only if a valid u32 value can be decoded. > > This is what I use here (as far as I tested it, it worked like a charm). > Do you wish I add a comment to describe this ? Probably best or I'll forget sometime down the line and think it looks crazy again ;) Thanks for the explanation. Jonathan > > Please let me know, > Best Regards, > Fabrice > > >> stm32_adc_chan_init_one(indio_dev, &channels[scan_index], > >> &adc_info->channels[val], > >> - scan_index); > >> + scan_index, smp); > >> scan_index++; > >> } > >> > >> @@ -1755,6 +1879,7 @@ static int stm32_adc_remove(struct platform_device > >> *pdev) > >> .clk_required = true, > >> .start_conv = stm32f4_adc_start_conv, > >> .stop_conv = stm32f4_adc_stop_conv, > >> + .smp_cycles = stm32f4_adc_smp_cycles, > >> }; > >> > >> static const struct stm32_adc_cfg stm32h7_adc_cfg = { > >> @@ -1766,6 +1891,7 @@ static int stm32_adc_remove(struct platform_device > >> *pdev) > >> .stop_conv = stm32h7_adc_stop_conv, > >> .prepare = stm32h7_adc_prepare, > >> .unprepare = stm32h7_adc_unprepare, > >> + .smp_cycles = stm32h7_adc_smp_cycles, > >> }; > >> > >> static const struct of_device_id stm32_adc_of_match[] = { > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-iio" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html
