Hi Jonathan,
On Sun, Jan 09, 2022 at 04:00:09PM +0000, Jonathan Cameron wrote:
> On Fri, 7 Jan 2022 10:35:27 +0100
> Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> wrote:
>
> > Add read_raw() support to make use of iio_hwmon and other iio clients.
> >
> > Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
> Hi Oleksij
>
> Main questions in here are around settling time and the interface used for that.
>
> > ---
> > drivers/iio/adc/ti-tsc2046.c | 114 ++++++++++++++++++++++++++++++++---
> > 1 file changed, 106 insertions(+), 8 deletions(-)
> >
> > @@ -252,16 +266,47 @@ static u16 tsc2046_adc_get_value(struct tsc2046_adc_atom *buf)
> > static int tsc2046_adc_read_one(struct tsc2046_adc_priv *priv, int ch_idx,
> > u32 *effective_speed_hz)
> > {
> > + struct tsc2046_adc_ch_cfg *ch = &priv->ch_cfg[ch_idx];
> > + struct tsc2046_adc_atom *rx_buf, *tx_buf;
> > + unsigned int val, val_normalized = 0;
> > + int ret, i, count_skip = 0, max_count;
> > struct spi_transfer xfer;
> > struct spi_message msg;
> > - int ret;
> > + u8 cmd;
> > +
> > + if (!effective_speed_hz) {
> > + count_skip = tsc2046_adc_time_to_count(priv, ch->settling_time_us);
> > + max_count = count_skip + ch->oversampling_ratio;
> > + } else {
> > + max_count = 1;
> > + }
> > +
> > + tx_buf = kcalloc(max_count, sizeof(*tx_buf), GFP_KERNEL);
> > + if (!tx_buf)
> > + return -ENOMEM;
> > +
> > + rx_buf = kcalloc(max_count, sizeof(*rx_buf), GFP_KERNEL);
> > + if (!rx_buf) {
> > + ret = -ENOMEM;
> > + goto free_tx;
> > + }
>
> I guess these are fine to do everytime because you expect this to be used in
> paths which aren't called at a particularly high frequency?
Yes, this was my assumption as well. Instead of preallocating buffer of
max size, I hope it is less ugly.
> These buffers could get rather large so maybe you need a cap on settling time?
What do you mean by "cap on settling"?
>
> > +
> > + /*
> > + * Do not enable automatic power down on working samples. Otherwise the
> > + * plates will never be completely charged.
> > + */
> > + cmd = tsc2046_adc_get_cmd(priv, ch_idx, true);
> > +
> > + for (i = 0; i < max_count - 1; i++)
> > + tx_buf[i].cmd = cmd;
> > +
> > + /* automatically power down on last sample */
> > + tx_buf[i].cmd = tsc2046_adc_get_cmd(priv, ch_idx, false);
> >
> > memset(&xfer, 0, sizeof(xfer));
> > - priv->tx_one->cmd = tsc2046_adc_get_cmd(priv, ch_idx, false);
> > - priv->tx_one->data = 0;
> > - xfer.tx_buf = priv->tx_one;
> > - xfer.rx_buf = priv->rx_one;
>
> Are these used for anything else? If not probably need to drop them and
> their allocation.
done
> > - xfer.len = sizeof(*priv->tx_one);
> > + xfer.tx_buf = tx_buf;
> > + xfer.rx_buf = rx_buf;
> > + xfer.len = sizeof(*tx_buf) * max_count;
>
> This could be very big and more than possible some spi controllers will fail
> it (or does the SPI core handle splitting very large transfers?) Maybe a loop
> is needed with smaller fixed size transfers?
I can't exclude possible issue with some of SPI drivers. But SPI level
optimizations should be done on SPI driver or framework level.
> > spi_message_init_with_transfers(&msg, &xfer, 1);
> >
> > /*
> > @@ -272,13 +317,25 @@ static int tsc2046_adc_read_one(struct tsc2046_adc_priv *priv, int ch_idx,
> > if (ret) {
> > dev_err_ratelimited(&priv->spi->dev, "SPI transfer failed %pe\n",
> > ERR_PTR(ret));
> > + *val2 = chan->scan_type.realbits;
> > + return IIO_VAL_FRACTIONAL_LOG2;
> > + case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> > + *val = priv->ch_cfg[chan->channel].oversampling_ratio;
> > + return IIO_VAL_INT;
> > + case IIO_CHAN_INFO_DEBOUNCE_COUNT:
>
> These are unusual. I think they've only been used for the more literal bounce suppression
> of a human step counting algorithm.
>
> I'd probably not expect to see the both even if we decide this is applicable.
Ok, i do not need this information so far. I'll remove it
> > + *val = tsc2046_adc_time_to_count(priv,
> > + priv->ch_cfg[chan->channel].settling_time_us);
>
> Setting time is often about external circuitry so it's a bit unusual to expose
> it to userspace rather than making it a device tree property and just making
> sure the driver doesn't provide a reading until appropriate debounce has passed.
> Here is coming from DT anyway, so what benefit do these two read only channel
> properties provide?
No benefit. Will remove it.
Regards,
Oleksij
--
Pengutronix e.K. | |
Steuerwalder Str. 21 | http://www.pengutronix.de/ |
31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
