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Date: Mon, 24 Jun 2024 15:33:01 +0200
From: Guillaume Stols <gstols@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Lars-Peter Clausen <lars@...afoo.de>,
Michael Hennerich <Michael.Hennerich@...log.com>, linux-iio@...r.kernel.org,
linux-kernel@...r.kernel.org, jstephan@...libre.com, dlechner@...libre.com
Subject: Re: [PATCH v2] iio: adc: ad7606: remove frstdata check for serial
mode
On 6/23/24 17:54, Jonathan Cameron wrote:
> On Tue, 18 Jun 2024 13:45:00 +0000
> Guillaume Stols <gstols@...libre.com> wrote:
>
>> Frstdata pin is set high during the first sample's transmission and then
>> set low. This code chunk attempts to recover from an eventual glitch in
>> the clock by checking frstdata state after reading the first channel's
>> sample. Currently, in serial mode, this check happens AFTER the 16th
>> pulse, and if frstdata is not set it resets the device and returns EINVAL.
>> According to the datasheet, "The FRSTDATA output returns to a logic low
>> following the 16th SCLK falling edge.", thus after the 16th pulse, the
>> check will always be true, and the driver will not work as expected. Thus
>> it must be removed for serial mode.
> when you say will not work as expected, is this is normal circumstances, or
> when dealing with a clock glitch? i.e. should this have a fixes tag and
> got upstream asap or is it just cleaning up a corner case and can wait for
> now?
>
> One trivial comment inline.
>
> Jonathan
It completely prevents the driver to work when adi, first-data
(optional) is defined in the DT.
So I guess anyone having the driver working with the serial interface
right now did not define frstdata in the DT.
However, for someone new that sets adi, first-data in the DT, it is not
very straightforward to spot where the issue is.
>
>> Signed-off-by: Guillaume Stols <gstols@...libre.com>
>> ---
>> Changes in v2:
>> - Remove frstdata check only for the serial interface as suggested by
>> Michael Hennerich.
>> - Link to v1: https://lore.kernel.org/r/20240417-cleanup-ad7606-v1-1-5c2a29662c0a@baylibre.com
>> ---
>> drivers/iio/adc/ad7606.c | 28 ++-----------------------
>> drivers/iio/adc/ad7606.h | 2 ++
>> drivers/iio/adc/ad7606_par.c | 49 +++++++++++++++++++++++++++++++++++++++++---
>> 3 files changed, 50 insertions(+), 29 deletions(-)
>>
>> diff --git a/drivers/iio/adc/ad7606.c b/drivers/iio/adc/ad7606.c
>> index 3a417595294f..c321c6ef48df 100644
>> --- a/drivers/iio/adc/ad7606.c
>> +++ b/drivers/iio/adc/ad7606.c
>> @@ -49,7 +49,7 @@ static const unsigned int ad7616_oversampling_avail[8] = {
>> 1, 2, 4, 8, 16, 32, 64, 128,
>> };
>>
>> -static int ad7606_reset(struct ad7606_state *st)
>> +int ad7606_reset(struct ad7606_state *st)
>> {
>> if (st->gpio_reset) {
>> gpiod_set_value(st->gpio_reset, 1);
>> @@ -60,6 +60,7 @@ static int ad7606_reset(struct ad7606_state *st)
>>
>> return -ENODEV;
>> }
>> +EXPORT_SYMBOL_NS_GPL(ad7606_reset, IIO_AD7606);
>>
>> static int ad7606_reg_access(struct iio_dev *indio_dev,
>> unsigned int reg,
>> @@ -88,31 +89,6 @@ static int ad7606_read_samples(struct ad7606_state *st)
>> {
>> unsigned int num = st->chip_info->num_channels - 1;
>> u16 *data = st->data;
>> - int ret;
>> -
>> - /*
>> - * The frstdata signal is set to high while and after reading the sample
>> - * of the first channel and low for all other channels. This can be used
>> - * to check that the incoming data is correctly aligned. During normal
>> - * operation the data should never become unaligned, but some glitch or
>> - * electrostatic discharge might cause an extra read or clock cycle.
>> - * Monitoring the frstdata signal allows to recover from such failure
>> - * situations.
>> - */
>> -
>> - if (st->gpio_frstdata) {
>> - ret = st->bops->read_block(st->dev, 1, data);
>> - if (ret)
>> - return ret;
>> -
>> - if (!gpiod_get_value(st->gpio_frstdata)) {
>> - ad7606_reset(st);
>> - return -EIO;
>> - }
>> -
>> - data++;
>> - num--;
>> - }
>>
>> return st->bops->read_block(st->dev, num, data);
>> }
>> diff --git a/drivers/iio/adc/ad7606.h b/drivers/iio/adc/ad7606.h
>> index 0c6a88cc4695..6649e84d25de 100644
>> --- a/drivers/iio/adc/ad7606.h
>> +++ b/drivers/iio/adc/ad7606.h
>> @@ -151,6 +151,8 @@ int ad7606_probe(struct device *dev, int irq, void __iomem *base_address,
>> const char *name, unsigned int id,
>> const struct ad7606_bus_ops *bops);
>>
>> +int ad7606_reset(struct ad7606_state *st);
>> +
>> enum ad7606_supported_device_ids {
>> ID_AD7605_4,
>> ID_AD7606_8,
>> diff --git a/drivers/iio/adc/ad7606_par.c b/drivers/iio/adc/ad7606_par.c
>> index d8408052262e..1f7050297b64 100644
>> --- a/drivers/iio/adc/ad7606_par.c
>> +++ b/drivers/iio/adc/ad7606_par.c
>> @@ -7,6 +7,7 @@
>>
>> #include <linux/mod_devicetable.h>
>> #include <linux/module.h>
>> +#include <linux/gpio/consumer.h>
>> #include <linux/platform_device.h>
>> #include <linux/types.h>
>> #include <linux/err.h>
>> @@ -21,8 +22,30 @@ static int ad7606_par16_read_block(struct device *dev,
>> struct iio_dev *indio_dev = dev_get_drvdata(dev);
>> struct ad7606_state *st = iio_priv(indio_dev);
>>
>> - insw((unsigned long)st->base_address, buf, count);
>>
>> + /*
>> + * On the parallel interface, the frstdata signal is set to high while
>> + * and after reading the sample of the first channel and low for all
>> + * other channels. This can be used to check that the incoming data is
>> + * correctly aligned. During normal operation the data should never
>> + * become unaligned, but some glitch or electrostatic discharge might
>> + * cause an extra read or clock cycle. Monitoring the frstdata signal
>> + * allows to recover from such failure situations.
>> + */
>> + int num = count;
>> + u16 *_buf = buf;
>> +
>> + if (st->gpio_frstdata) {
>> + insw((unsigned long)st->base_address, _buf, 1);
>> + if (!gpiod_get_value(st->gpio_frstdata)) {
>> + ad7606_reset(st);
>> + return -EIO;
>> + }
>> + _buf++;
>> + num--;
>> + }
>> + insw((unsigned long)st->base_address, _buf, num)
>> +;
> Seems this slipped onto the next line.
> Make sure to run checkpatch which I would have thought would catch this.
>
>> return 0;
>> }
>>
>> @@ -35,8 +58,28 @@ static int ad7606_par8_read_block(struct device *dev,
>> {
>> struct iio_dev *indio_dev = dev_get_drvdata(dev);
>> struct ad7606_state *st = iio_priv(indio_dev);
>> -
>> - insb((unsigned long)st->base_address, buf, count * 2);
>> + /*
>> + * On the parallel interface, the frstdata signal is set to high while
>> + * and after reading the sample of the first channel and low for all
>> + * other channels. This can be used to check that the incoming data is
>> + * correctly aligned. During normal operation the data should never
>> + * become unaligned, but some glitch or electrostatic discharge might
>> + * cause an extra read or clock cycle. Monitoring the frstdata signal
>> + * allows to recover from such failure situations.
>> + */
>> + int num = count;
>> + u16 *_buf = buf;
>> +
>> + if (st->gpio_frstdata) {
>> + insb((unsigned long)st->base_address, _buf, 2);
>> + if (!gpiod_get_value(st->gpio_frstdata)) {
>> + ad7606_reset(st);
>> + return -EIO;
>> + }
>> + _buf++;
>> + num--;
>> + }
>> + insb((unsigned long)st->base_address, _buf, num * 2);
>>
>> return 0;
>> }
>>
>> ---
>> base-commit: 07d4d0bb4a8ddcc463ed599b22f510d5926c2495
>> change-id: 20240416-cleanup-ad7606-161e2ed9818b
>>
>> Best regards,
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