[PATCH 0/1] Fix ltc2983 probing

[PATCH 0/1] Fix ltc2983 probing

[Nuno Sá]

The issue was reported by Drew [1]. I tested this fix on a rpi and it
works. It would be nice to have a tested-by tag for this on your
platform Drew.

On top of the reported issue, the patch also fixes device binding and
unbinding since that would also fail (that also obviously failed on
rpi). The same goes for module unloading and loading.

[1]: https://marc.info/?l=linux-iio&m=162829198205250&w=2

Nuno Sá (1):
  iio: ltc2983: fix device probe

 drivers/iio/temperature/ltc2983.c | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

-- 
2.32.0

[PATCH 1/1] iio: ltc2983: fix device probe

[Nuno Sá]

There is no reason to assume that the irq rising edge (indicating that
the device start up phase is done) will happen after we request the irq.
If the device is already up by the time we request it, the call to
'wait_for_completion_timeout()' will timeout and we will fail the device
probe even though there's nothing wrong.

This patch fixes it by just polling the status register until we get the
indication that the device is up and running. As a side effect of this
fix, requesting the irq is also moved to after the setup function.

Fixes: f110f3188e563 ("iio: temperature: Add support for LTC2983")
Reported-by: Drew Fustini <drew@pdp7.com>
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
---
 drivers/iio/temperature/ltc2983.c | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/drivers/iio/temperature/ltc2983.c b/drivers/iio/temperature/ltc2983.c
index 3b5ba26d7d86..c6c4877bdcff 100644
--- a/drivers/iio/temperature/ltc2983.c
+++ b/drivers/iio/temperature/ltc2983.c
@@ -89,6 +89,8 @@
 
 #define	LTC2983_STATUS_START_MASK	BIT(7)
 #define	LTC2983_STATUS_START(x)		FIELD_PREP(LTC2983_STATUS_START_MASK, x)
+#define        LTC2983_STATUS_UP_MASK	GENMASK(7, 6)
+#define        LTC2983_STATUS_UP(reg)	FIELD_GET(LTC2983_STATUS_UP_MASK, reg)
 
 #define	LTC2983_STATUS_CHAN_SEL_MASK	GENMASK(4, 0)
 #define	LTC2983_STATUS_CHAN_SEL(x) \
@@ -1362,13 +1364,21 @@ static int ltc2983_parse_dt(struct ltc2983_data *st)
 
 static int ltc2983_setup(struct ltc2983_data *st, bool assign_iio)
 {
-	u32 iio_chan_t = 0, iio_chan_v = 0, chan, iio_idx = 0;
+	u32 iio_chan_t = 0, iio_chan_v = 0, chan, iio_idx = 0, status = 0;
 	int ret;
-	unsigned long time;
+	unsigned long time = 10;
 
 	/* make sure the device is up */
-	time = wait_for_completion_timeout(&st->completion,
-					    msecs_to_jiffies(250));
+	do {
+		ret = regmap_read(st->regmap, LTC2983_STATUS_REG, &status);
+		if (ret)
+			return ret;
+		/* start bit (7) is 0 and done bit (6) is 1 */
+		if (LTC2983_STATUS_UP(status) == 1)
+			break;
+
+		msleep(25);
+	} while (--time);
 
 	if (!time) {
 		dev_err(&st->spi->dev, "Device startup timed out\n");
@@ -1492,10 +1502,11 @@ static int ltc2983_probe(struct spi_device *spi)
 	ret = ltc2983_parse_dt(st);
 	if (ret)
 		return ret;
-	/*
-	 * let's request the irq now so it is used to sync the device
-	 * startup in ltc2983_setup()
-	 */
+
+	ret = ltc2983_setup(st, true);
+	if (ret)
+		return ret;
+
 	ret = devm_request_irq(&spi->dev, spi->irq, ltc2983_irq_handler,
 			       IRQF_TRIGGER_RISING, name, st);
 	if (ret) {
@@ -1503,10 +1514,6 @@ static int ltc2983_probe(struct spi_device *spi)
 		return ret;
 	}
 
-	ret = ltc2983_setup(st, true);
-	if (ret)
-		return ret;
-
 	indio_dev->name = name;
 	indio_dev->num_channels = st->iio_channels;
 	indio_dev->channels = st->iio_chan;
-- 
2.32.0

Re: [PATCH 1/1] iio: ltc2983: fix device probe

[Drew Fustini]

On Tue, Aug 10, 2021 at 04:56:53PM +0200, Nuno Sá wrote:
> There is no reason to assume that the irq rising edge (indicating that
> the device start up phase is done) will happen after we request the irq.
> If the device is already up by the time we request it, the call to
> 'wait_for_completion_timeout()' will timeout and we will fail the device
> probe even though there's nothing wrong.
> 
> This patch fixes it by just polling the status register until we get the
> indication that the device is up and running. As a side effect of this
> fix, requesting the irq is also moved to after the setup function.
> 
> Fixes: f110f3188e563 ("iio: temperature: Add support for LTC2983")
> Reported-by: Drew Fustini <drew@pdp7.com>
> Signed-off-by: Nuno Sá <nuno.sa@analog.com>
> ---
>  drivers/iio/temperature/ltc2983.c | 31 +++++++++++++++++++------------
>  1 file changed, 19 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/iio/temperature/ltc2983.c b/drivers/iio/temperature/ltc2983.c
> index 3b5ba26d7d86..c6c4877bdcff 100644
> --- a/drivers/iio/temperature/ltc2983.c
> +++ b/drivers/iio/temperature/ltc2983.c
> @@ -89,6 +89,8 @@
>  
>  #define	LTC2983_STATUS_START_MASK	BIT(7)
>  #define	LTC2983_STATUS_START(x)		FIELD_PREP(LTC2983_STATUS_START_MASK, x)
> +#define        LTC2983_STATUS_UP_MASK	GENMASK(7, 6)
> +#define        LTC2983_STATUS_UP(reg)	FIELD_GET(LTC2983_STATUS_UP_MASK, reg)
>  
>  #define	LTC2983_STATUS_CHAN_SEL_MASK	GENMASK(4, 0)
>  #define	LTC2983_STATUS_CHAN_SEL(x) \
> @@ -1362,13 +1364,21 @@ static int ltc2983_parse_dt(struct ltc2983_data *st)
>  
>  static int ltc2983_setup(struct ltc2983_data *st, bool assign_iio)
>  {
> -	u32 iio_chan_t = 0, iio_chan_v = 0, chan, iio_idx = 0;
> +	u32 iio_chan_t = 0, iio_chan_v = 0, chan, iio_idx = 0, status = 0;
>  	int ret;
> -	unsigned long time;
> +	unsigned long time = 10;
>  
>  	/* make sure the device is up */
> -	time = wait_for_completion_timeout(&st->completion,
> -					    msecs_to_jiffies(250));
> +	do {
> +		ret = regmap_read(st->regmap, LTC2983_STATUS_REG, &status);
> +		if (ret)
> +			return ret;
> +		/* start bit (7) is 0 and done bit (6) is 1 */
> +		if (LTC2983_STATUS_UP(status) == 1)
> +			break;
> +
> +		msleep(25);
> +	} while (--time);
>  
>  	if (!time) {
>  		dev_err(&st->spi->dev, "Device startup timed out\n");
> @@ -1492,10 +1502,11 @@ static int ltc2983_probe(struct spi_device *spi)
>  	ret = ltc2983_parse_dt(st);
>  	if (ret)
>  		return ret;
> -	/*
> -	 * let's request the irq now so it is used to sync the device
> -	 * startup in ltc2983_setup()
> -	 */
> +
> +	ret = ltc2983_setup(st, true);
> +	if (ret)
> +		return ret;
> +
>  	ret = devm_request_irq(&spi->dev, spi->irq, ltc2983_irq_handler,
>  			       IRQF_TRIGGER_RISING, name, st);
>  	if (ret) {
> @@ -1503,10 +1514,6 @@ static int ltc2983_probe(struct spi_device *spi)
>  		return ret;
>  	}
>  
> -	ret = ltc2983_setup(st, true);
> -	if (ret)
> -		return ret;
> -
>  	indio_dev->name = name;
>  	indio_dev->num_channels = st->iio_channels;
>  	indio_dev->channels = st->iio_chan;
> -- 
> 2.32.0
> 

I have tested this on my custom Zynq-7000 board and the probe completes
okay. The read of LTC2983_STATUS_REG returns 0x40 on the first attempt
which is good. I am also able to read channels through sysfs. I have not
tried suspend and resume as that is not configured on this system.

Reviewed-by: Drew Fustini <drew@pdp7.com>
Tested-by: Drew Fustini <drew@pdp7.com>

Thanks for fixing,
Drew

RE: [PATCH 1/1] iio: ltc2983: fix device probe

[Sa, Nuno]

> -----Original Message-----
> From: Drew Fustini <drew@pdp7.com>
> Sent: Wednesday, August 11, 2021 12:03 AM
> To: Sa, Nuno <Nuno.Sa@analog.com>
> Cc: linux-iio@vger.kernel.org; =Jonathan Cameron <jic23@kernel.org>;
> Lars-Peter Clausen <lars@metafoo.de>
> Subject: Re: [PATCH 1/1] iio: ltc2983: fix device probe
>  
> On Tue, Aug 10, 2021 at 04:56:53PM +0200, Nuno Sá wrote:
> > There is no reason to assume that the irq rising edge (indicating that
> > the device start up phase is done) will happen after we request the
> irq.
> > If the device is already up by the time we request it, the call to
> > 'wait_for_completion_timeout()' will timeout and we will fail the
> device
> > probe even though there's nothing wrong.
> >
> > This patch fixes it by just polling the status register until we get the
> > indication that the device is up and running. As a side effect of this
> > fix, requesting the irq is also moved to after the setup function.
> >
> > Fixes: f110f3188e563 ("iio: temperature: Add support for LTC2983")
> > Reported-by: Drew Fustini <drew@pdp7.com>
> > Signed-off-by: Nuno Sá <nuno.sa@analog.com>
> > ---
> >  drivers/iio/temperature/ltc2983.c | 31 +++++++++++++++++++------
> ------
> >  1 file changed, 19 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/iio/temperature/ltc2983.c
> b/drivers/iio/temperature/ltc2983.c
> > index 3b5ba26d7d86..c6c4877bdcff 100644
> > --- a/drivers/iio/temperature/ltc2983.c
> > +++ b/drivers/iio/temperature/ltc2983.c
> > @@ -89,6 +89,8 @@
> >
> >  #define	LTC2983_STATUS_START_MASK	BIT(7)
> >  #define	LTC2983_STATUS_START(x)
> 	FIELD_PREP(LTC2983_STATUS_START_MASK, x)
> > +#define        LTC2983_STATUS_UP_MASK	GENMASK(7, 6)
> > +#define        LTC2983_STATUS_UP(reg)
> 	FIELD_GET(LTC2983_STATUS_UP_MASK, reg)
> >
> >  #define	LTC2983_STATUS_CHAN_SEL_MASK	GENMASK(4, 0)
> >  #define	LTC2983_STATUS_CHAN_SEL(x) \
> > @@ -1362,13 +1364,21 @@ static int ltc2983_parse_dt(struct
> ltc2983_data *st)
> >
> >  static int ltc2983_setup(struct ltc2983_data *st, bool assign_iio)
> >  {
> > -	u32 iio_chan_t = 0, iio_chan_v = 0, chan, iio_idx = 0;
> > +	u32 iio_chan_t = 0, iio_chan_v = 0, chan, iio_idx = 0, status = 0;
> >  	int ret;
> > -	unsigned long time;
> > +	unsigned long time = 10;
> >
> >  	/* make sure the device is up */
> > -	time = wait_for_completion_timeout(&st->completion,
> > -					    msecs_to_jiffies(250));
> > +	do {
> > +		ret = regmap_read(st->regmap,
> LTC2983_STATUS_REG, &status);
> > +		if (ret)
> > +			return ret;
> > +		/* start bit (7) is 0 and done bit (6) is 1 */
> > +		if (LTC2983_STATUS_UP(status) == 1)
> > +			break;
> > +
> > +		msleep(25);
> > +	} while (--time);
> >
> >  	if (!time) {
> >  		dev_err(&st->spi->dev, "Device startup timed out\n");
> > @@ -1492,10 +1502,11 @@ static int ltc2983_probe(struct spi_device
> *spi)
> >  	ret = ltc2983_parse_dt(st);
> >  	if (ret)
> >  		return ret;
> > -	/*
> > -	 * let's request the irq now so it is used to sync the device
> > -	 * startup in ltc2983_setup()
> > -	 */
> > +
> > +	ret = ltc2983_setup(st, true);
> > +	if (ret)
> > +		return ret;
> > +
> >  	ret = devm_request_irq(&spi->dev, spi->irq,
> ltc2983_irq_handler,
> >  			       IRQF_TRIGGER_RISING, name, st);
> >  	if (ret) {
> > @@ -1503,10 +1514,6 @@ static int ltc2983_probe(struct spi_device
> *spi)
> >  		return ret;
> >  	}
> >
> > -	ret = ltc2983_setup(st, true);
> > -	if (ret)
> > -		return ret;
> > -
> >  	indio_dev->name = name;
> >  	indio_dev->num_channels = st->iio_channels;
> >  	indio_dev->channels = st->iio_chan;
> > --
> > 2.32.0
> >
> 
> I have tested this on my custom Zynq-7000 board and the probe
> completes
> okay. The read of LTC2983_STATUS_REG returns 0x40 on the first
> attempt
> which is good. I am also able to read channels through sysfs. I have not
> tried suspend and resume as that is not configured on this system.

Hi,

Thanks for testing. During my tests I kind of emulated this by adding
a devm_action which would put the device to sleep on the unbind path.
Hence, unbinding + binding the device will cause a sleep + wake up on it.
In this case I saw  ~75 ms for it to come up. I read some 0's, 0x80 
(as specified in the datasheet) and lastly 0x40.


Jonathan, I noticed some odd indentation in the new defines. If there's
no other reason for a v2, it would be nice if you could fix this when applying :)

As a side note, I'm also aware that you prefer to see FIELD_{PREP|GET} applied
inline in the code but in this case I made it like this to be consistent with the 
rest of the driver.

- Nuno Sá

RE: [PATCH 1/1] iio: ltc2983: fix device probe

[Sa, Nuno]

> -----Original Message-----
> From: Andy Shevchenko <andy.shevchenko@gmail.com>
> Sent: Wednesday, August 11, 2021 8:15 AM
> To: Sa, Nuno <Nuno.Sa@analog.com>
> Cc: linux-iio@vger.kernel.org; =Jonathan Cameron <jic23@kernel.org>;
> Lars-Peter Clausen <lars@metafoo.de>; Drew Fustini
> <drew@pdp7.com>
> Subject: Re: [PATCH 1/1] iio: ltc2983: fix device probe
>  
> 
> 
> On Tuesday, August 10, 2021, Nuno Sá <nuno.sa@analog.com
> <mailto:nuno.sa@analog.com> > wrote:
> 
> 
> 	There is no reason to assume that the irq rising edge (indicating
> that
> 	the device start up phase is done) will happen after we request
> the irq.
> 	If the device is already up by the time we request it, the call to
> 	'wait_for_completion_timeout()' will timeout and we will fail
> the device
> 	probe even though there's nothing wrong.
> 
> 	This patch fixes it by just polling the status register until we get
> the
> 	indication that the device is up and running. As a side effect of
> this
> 	fix, requesting the irq is also moved to after the setup function.
> 
> 	Fixes: f110f3188e563 ("iio: temperature: Add support for
> LTC2983")
> 	Reported-by: Drew Fustini <drew@pdp7.com
> <mailto:drew@pdp7.com> >
> 	Signed-off-by: Nuno Sá <nuno.sa@analog.com
> <mailto:nuno.sa@analog.com> >
> 	---
> 	 drivers/iio/temperature/ltc2983.c | 31
> +++++++++++++++++++------------
> 	 1 file changed, 19 insertions(+), 12 deletions(-)
> 
> 	diff --git a/drivers/iio/temperature/ltc2983.c
> b/drivers/iio/temperature/ltc2983.c
> 	index 3b5ba26d7d86..c6c4877bdcff 100644
> 	--- a/drivers/iio/temperature/ltc2983.c
> 	+++ b/drivers/iio/temperature/ltc2983.c
> 	@@ -89,6 +89,8 @@
> 
> 	 #define        LTC2983_STATUS_START_MASK       BIT(7)
> 	 #define        LTC2983_STATUS_START(x)
> FIELD_PREP(LTC2983_STATUS_START_MASK, x)
> 	+#define        LTC2983_STATUS_UP_MASK  GENMASK(7, 6)
> 	+#define        LTC2983_STATUS_UP(reg)
> FIELD_GET(LTC2983_STATUS_UP_MASK, reg)
> 
> 	 #define        LTC2983_STATUS_CHAN_SEL_MASK
> GENMASK(4, 0)
> 	 #define        LTC2983_STATUS_CHAN_SEL(x) \
> 	@@ -1362,13 +1364,21 @@ static int ltc2983_parse_dt(struct
> ltc2983_data *st)
> 
> 	 static int ltc2983_setup(struct ltc2983_data *st, bool assign_iio)
> 	 {
> 	-       u32 iio_chan_t = 0, iio_chan_v = 0, chan, iio_idx = 0;
> 	+       u32 iio_chan_t = 0, iio_chan_v = 0, chan, iio_idx = 0, status
> = 0;
> 	        int ret;
> 	-       unsigned long time;
> 	+       unsigned long time = 10;
> 
> 	        /* make sure the device is up */
> 	-       time = wait_for_completion_timeout(&st->completion,
> 	-                                           msecs_to_jiffies(250));
> 	+       do {
> 	+               ret = regmap_read(st->regmap,
> LTC2983_STATUS_REG, &status);
> 	+               if (ret)
> 	+                       return ret;
> 	+               /* start bit (7) is 0 and done bit (6) is 1 */
> 	+               if (LTC2983_STATUS_UP(status) == 1)
> 	+                       break;
> 	+
> 	+               msleep(25);
> 	+       } while (--time);
> 
> 
> 
> NIH regmap_read_poll_timeout()

Nice helper. Will send a v2 with it...

- Nuno Sá