Re: [PATCH v3 1/2] iio: adc: mt6360: Add ADC driver for MT6360

From: Gene Chen
Date: Wed Sep 09 2020 - 03:39:29 EST

Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> 於 2020年9月8日 週二 下午9:00寫道：
>
> ...
>
> > > > > > +#include <linux/completion.h>
> > > > > > +#include <linux/interrupt.h>
> > > > > > +#include <linux/iio/buffer.h>
> > > > > > +#include <linux/iio/iio.h>
> > > > > > +#include <linux/iio/trigger_consumer.h>
> > > > > > +#include <linux/iio/triggered_buffer.h>
> > > > > > +#include <linux/irq.h>
> > > > > > +#include <linux/kernel.h>
> > > > > > +#include <linux/ktime.h>
> > > > > > +#include <linux/module.h>
> > > > > > +#include <linux/mutex.h>
> > > > > > +#include <linux/platform_device.h>
> > > > > > +#include <linux/regmap.h>
> > > > > > +
> > > > > > +#define MT6360_REG_PMUCHGCTRL3 0x313
> > > > > > +#define MT6360_REG_PMUADCCFG 0x356
> > > > > > +#define MT6360_REG_PMUADCRPT1 0x35A
> > > > > > +
> > > > > > +/* PMUCHGCTRL3 0x313 */
> > > > > > +#define MT6360_AICR_MASK 0xFC
> > > > > > +#define MT6360_AICR_SHFT 2
> > > > > > +#define MT6360_AICR_400MA 0x6
> > > > > > +/* PMUADCCFG 0x356 */
> > > > > > +#define MT6360_ADCEN_MASK 0x8000
> > > > > > +/* PMUADCRPT1 0x35A */
> > > > > > +#define MT6360_PREFERCH_MASK 0xF0
> > > > > > +#define MT6360_PREFERCH_SHFT 4
> > > > > > +#define MT6360_RPTCH_MASK 0x0F
> > > > > > +
> > > > > > +enum {
> > > > > > + MT6360_CHAN_USBID = 0,
> > > > > > + MT6360_CHAN_VBUSDIV5,
> > > > > > + MT6360_CHAN_VBUSDIV2,
> > > > > > + MT6360_CHAN_VSYS,
> > > > > > + MT6360_CHAN_VBAT,
> > > > > > + MT6360_CHAN_IBUS,
> > > > > > + MT6360_CHAN_IBAT,
> > > > > > + MT6360_CHAN_CHG_VDDP,
> > > > > > + MT6360_CHAN_TEMP_JC,
> > > > > > + MT6360_CHAN_VREF_TS,
> > > > > > + MT6360_CHAN_TS,
> > > > > > + MT6360_CHAN_MAX,
> > > > > > +};
> > > > > > +
> > > > > > +struct mt6360_adc_data {
> > > > > > + struct device *dev;
> > > > > > + struct regmap *regmap;
> > > > > > + struct completion adc_complete;
> > > > > > + struct mutex adc_lock;
> > > > > > + ktime_t last_off_timestamps[MT6360_CHAN_MAX];
> > > > > > + int irq;
> > > > > > +};
> > > > > > +
> > > > > > +static inline int mt6360_adc_val_converter(int val, int multiplier, int offset, int divisor)
> > > > > > +{
> > > > > > + return ((val * multiplier) + offset) / divisor;
> > > > >
> > > > > Why could we not report these values to userspace or consumer drivers and let
> > > > > them deal with the conversion if they actually needed it?
> > > > > Mapping this to
> > > > >
> > > > > (val + new_offset) * multiplier would be a little messy, but not too bad.
> > > > >
> > > > > The advantage would be that we would then be providing the data needed
> > > > > to get real units for values read from the buffers without having to
> > > > > do all the maths in kernel (without access to floating point).
> > > > >
> > > > >
> > > >
> > > > As above, if I use formula "(val + new_offset) * multiplier",
> > > > the junction temperature channel multiplier will be floating point
> > > > 1.05, i don't know how to express.
> > >
> > > As Andy mentioned, we do this all over the place.
> > > IIO_VAL_INT_PLUS_MICRO
> > >
> > > The key is that we want to push the burden of doing this maths to the user
> > > not the source.
> >
> > ACK.
> > Can I keep IIO_CHAN_INFO_PROCESSED function be reserved for user in
> > kernel space?
> >
>
> No. We have utility functions that will apply the multiplier as needed so
> there is no significant advantage in doing this and it won't be consistent
> with the majority of other drivers.
>

ACK, I will remove IIO_CHAN_INFO_PROCESSED.

> > >
> > > Often what is actually of interest is whether a temperature passed a threshold.
> > > In that case, you can transform the threshold into the units of the ADC (so the
> > > reverse directly to you would do with processed data) and only have to do the
> > > maths once per change of the threshold instead of for every sample.
> > >
> > > There are helper functions to do the maths for you, should you actually
> > > need SI units.
> > >
> >
> > ACK
> >
> > > >
> > > > > > +}
> > > > > > +
> > > > > > +static int mt6360_adc_convert_processed_val(struct mt6360_adc_data *info, int chan_idx, int *val)
> > > > > > +{
> > > > > > + unsigned int regval = 0;
> > > > > > + const struct converter {
> > > > > > + int multiplier;
> > > > > > + int offset;
> > > > > > + int divisor;
> > > > > > + } adc_converter[MT6360_CHAN_MAX] = {
> > > > > > + { 1250, 0, 1}, /* USBID */
> > > > > > + { 6250, 0, 1}, /* VBUSDIV5 */
> > > > > > + { 2500, 0, 1}, /* VBUSDIV2 */
> > > > > > + { 1250, 0, 1}, /* VSYS */
> > > > > > + { 1250, 0, 1}, /* VBAT */
> > > > > > + { 2500, 0, 1}, /* IBUS */
> > > > > > + { 2500, 0, 1}, /* IBAT */
> > > > > > + { 1250, 0, 1}, /* CHG_VDDP */
> > > > > > + { 105, -8000, 100}, /* TEMP_JC */
> > > > > > + { 1250, 0, 1}, /* VREF_TS */
> > > > > > + { 1250, 0, 1}, /* TS */
> > > > > > + }, sp_ibus_adc_converter = { 1900, 0, 1 }, *sel_converter;
> > > > > > + int ret;
> > > > > > +
> > > > > > + sel_converter = adc_converter + chan_idx;
> > > > > > + if (chan_idx == MT6360_CHAN_IBUS) {
> > > > > > + /* ibus chan will be affected by aicr config */
> > > > > > + /* if aicr < 400, apply the special ibus converter */
> > > > > > + ret = regmap_read(info->regmap, MT6360_REG_PMUCHGCTRL3, &regval);
> > > > > > + if (ret)
> > > > > > + return ret;
> > > > > > +
> > > > > > + regval = (regval & MT6360_AICR_MASK) >> MT6360_AICR_SHFT;
> > > > > > + if (regval < MT6360_AICR_400MA)
> > > > > > + sel_converter = &sp_ibus_adc_converter;
> > > > > > + }
> > > > > > +
> > > > > > + *val = mt6360_adc_val_converter(*val, sel_converter->multiplier, sel_converter->offset,
> > > > > > + sel_converter->divisor);
> > > > > > +
> > > > > > + return 0;
> > > > > > +}
> > > > > > +
> > > > > > +static int mt6360_adc_read_processed(struct mt6360_adc_data *mad, int channel, int *val)
> > > > > > +{
> > > > > > + u16 adc_enable;
> > > > > > + u8 rpt[3];
> > > > > > + ktime_t start_t, predict_end_t;
> > > > > > + long timeout;
> > > > > > + int value, ret;
> > > > > > +
> > > > > > + mutex_lock(&mad->adc_lock);
> > > > > > +
> > > > > > + /* select preferred channel that we want */
> > > > > > + ret = regmap_update_bits(mad->regmap, MT6360_REG_PMUADCRPT1, MT6360_PREFERCH_MASK,
> > > > > > + channel << MT6360_PREFERCH_SHFT);
> > > > > > + if (ret)
> > > > > > + goto out_adc;
> > > > > > +
> > > > > > + /* enable adc channel we want and adc_en */
> > > > > > + adc_enable = MT6360_ADCEN_MASK | BIT(channel);
> > > > > > + adc_enable = cpu_to_be16(adc_enable);
> > > > >
> > > > > Use a local be16 to store that. It will make it a little clearer
> > > > > that we are doing something 'unusual' here. Perhaps a comment on
> > > > > why this odd code exists would also help?
> > > > >
> > > >
> > > > ACK
> > > >
> > > > > > + ret = regmap_raw_write(mad->regmap, MT6360_REG_PMUADCCFG, (void *)&adc_enable, sizeof(u16));
> > > > > > + if (ret)
> > > > > > + goto out_adc;
> > > > > > +
> > > > > > + start_t = ktime_get();
> > > > > > + predict_end_t = ktime_add_ms(mad->last_off_timestamps[channel], 50);
> > > > > > +
> > > > > > + if (ktime_after(start_t, predict_end_t))
> > > > > > + predict_end_t = ktime_add_ms(start_t, 25);
> > > > > > + else
> > > > > > + predict_end_t = ktime_add_ms(start_t, 75);
> > > > > > +
> > > > > > + enable_irq(mad->irq);
> > > > > > +adc_retry:
> > > > > > + reinit_completion(&mad->adc_complete);
> > > > > > +
> > > > > > + /* wait for conversion to complete */
> > > > > > + timeout = wait_for_completion_timeout(&mad->adc_complete, msecs_to_jiffies(200));
> > > > > > + if (timeout == 0) {
> > > > > > + ret = -ETIMEDOUT;
> > > > > > + goto out_adc_conv;
> > > > > > + } else if (timeout < 0) {
> > > > > > + ret = -EINTR;
> > > > > > + goto out_adc_conv;
> > > > > > + }
> > > > > > +
> > > > > > + ret = regmap_raw_read(mad->regmap, MT6360_REG_PMUADCRPT1, rpt, sizeof(rpt));
> > > > > > + if (ret)
> > > > > > + goto out_adc_conv;
> > > > > > +
> > > > > > + /* check the current reported channel */
> > > > > > + if ((rpt[0] & MT6360_RPTCH_MASK) != channel) {
> > > > > > + dev_dbg(mad->dev, "not wanted channel report [%02x]\n", rpt[0]);
> > > > >
> > > > > This and the one below feel like error messages rather than debug ones.
> > > > >
> > > >
> > > > We have two function "battery zero current voltage(ZCV)" and "TypeC
> > > > OTP" will auto run ADC at background.
> > > > ZCV_EN will run VBAT_ADC when TA plug in, TypeC OTP will run TS_ADC
> > > > when TypeC attach.
> > > > We need to check report channel for ADC report data match is our desire channel.
> > >
> > > So there is firmware messing with it underneath? Oh goody.
> > > Add a comment explaining this.
> > >
> >
> > ACK, I try to write a comment as below
> >
> > /*
> > * There are two functions, ZCV and TypeC OTP, running ADC
> > VBAT and TS in background,
> > * and ADC samples are taken on a fixed frequency no matter
> > read the previous one or not.
> > * To avoid conflict need set minimum time threshold after
> > enable ADC and check report
> > * channel is the same.
> > * The worst case is run the same ADC twice and background
> > function is also running,
> > * ADC conversion sequence is desire channel before start ADC,
> > background ADC, desire
> > * channel after start ADC. So the minimum correct data is
> > three times of typical
> > * conversion time.
> > */
>
> Looks good.
>

ACK

> >
> > > >
> > > > > > + goto adc_retry;
> > > > > > + }
> > > > > > +
> > > > > > + if (!ktime_after(ktime_get(), predict_end_t)) {
> > > > > > + dev_dbg(mad->dev, "time is not after one adc_conv_t\n");
> > > > >
> > > > > Does this actually happen? If feels like we are being a bit over protective
> > > > > here. I'd definitely like to see a comment saying why this protection
> > > > > might be needed.
> > > > >
> > > >
> > > > When ADC_EN and MT6360_CHANx_EN is enable, the channel x will keep
> > > > running again and again
> > > > I supposed to get immediate data which is generated after I start it.
> > >
> > > Just to check my understanding.
> > >
> > > This is an edge triggered interrupt and it triggers every time a new sample
> > > is taken. Those samples are taken on a fixed frequency irrespective of whether
> > > we have read the previous one?
> > >
> >
> > Yes.
> > I use LEVEL_LOW trigger in latest review MFD patch.
>
> I'm not sure I follow that comment. How can you do that if it's a repeating
> edge trigger?
>

I implement "struct regmap_irq_chip" handle_post_irq ops,
In the end of handle irq, I set the re-trigger bit which will pull irq
high to low again if irq pin is low.

-static int mt6360_pmu_handle_post_irq(void *irq_drv_data)
-{
- struct mt6360_pmu_info *mpi = irq_drv_data;
-
- return regmap_update_bits(mpi->regmap,
- MT6360_PMU_IRQ_SET, MT6360_IRQ_RETRIG, MT6360_IRQ_RETRIG);
-}
-

> >
> > > >
> > > > When I disable ADC_CHANx_EN, the H/W logical ADC is still running.
> > > > If I run the same ADC immediately, I may get the old result about this channel.
> > > > MT6360 ADC typical conversation time is about 25ms.
> > > > So We need ignore which irq trigger below 25ms.
> > >
> > > Normal trick for this sort of case is to just not use the interrupt.
> > > Just read after 25+delta msecs and you are guaranteed to get the right answer.
> > >
> > >
> >
> > ACK, I will try to use polling
> > Is the pseudocode correct?
> >
> > mdelay(predict_end_t);
> > while (true) {
> > read adc event is occured
> > check report channel is the same
> > if the same, read report ADC data and break while loop
> > else msleep(per ADC conversion time)
> > }
>
> Looks correct to me. We should 'know' the event has happened but
> still need to check the channel is the expected one.
>

There is a comment in our internal discuss.
If I use msleep as polling interval, the worst case will cause
additional wait time nearly one polling interval.
Can I keep using interrupt for saving time?

> ...
>