[PATCH v2 0/2] accel: adxl380: Improve data reading from FIFO

[PATCH v2 0/2] accel: adxl380: Improve data reading from FIFO

[Francesco Lavra]

Patch 1 fixes a bug that might cause the adxl380 interrupt handler
to read from the sensor FIFO more entries than actually present.
Patch 2 optimizes transfer of FIFO data by minimizing transport protocol
overhead.

Changes from v1 [1]:
- replaced 2 with sizeof(*st->fifo_buf) in adxl380_irq_handler (Jonathan)

[1] https://lore.kernel.org/linux-iio/20260106193627.3989930-1-flavra@baylibre.com/T/

Francesco Lavra (2):
  iio: accel: adxl380: Avoid reading more entries than present in FIFO
  iio: accel: adxl380: Optimize reading of FIFO entries in interrupt
    handler

 drivers/iio/accel/adxl380.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

-- 
2.39.5

[PATCH v2 1/2] iio: accel: adxl380: Avoid reading more entries than present in FIFO

[Francesco Lavra]

The interrupt handler reads FIFO entries in batches of N samples, where N
is the number of scan elements that have been enabled. However, the sensor
fills the FIFO one sample at a time, even when more than one channel is
enabled. Therefore,the number of entries reported by the FIFO status
registers may not be a multiple of N; if this number is not a multiple, the
number of entries read from the FIFO may exceed the number of entries
actually present.

To fix the above issue, round down the number of FIFO entries read from the
status registers so that it is always a multiple of N.

Fixes: df36de13677a ("iio: accel: add ADXL380 driver")
Signed-off-by: Francesco Lavra <flavra@baylibre.com>
---
 drivers/iio/accel/adxl380.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/iio/accel/adxl380.c b/drivers/iio/accel/adxl380.c
index ac20fcfd4e22..650cdbffd4a7 100644
--- a/drivers/iio/accel/adxl380.c
+++ b/drivers/iio/accel/adxl380.c
@@ -964,6 +964,7 @@ static irqreturn_t adxl380_irq_handler(int irq, void  *p)
 	if (ret)
 		return IRQ_HANDLED;
 
+	fifo_entries = rounddown(fifo_entries, st->fifo_set_size);
 	for (i = 0; i < fifo_entries; i += st->fifo_set_size) {
 		ret = regmap_noinc_read(st->regmap, ADXL380_FIFO_DATA,
 					&st->fifo_buf[i],
-- 
2.39.5

[PATCH v2 2/2] iio: accel: adxl380: Optimize reading of FIFO entries in interrupt handler

[Francesco Lavra]

In order to minimize the time required for transferring FIFO data from the
sensor to the host machine, perform the read from the FIFO in a single call
to regmap_bulk_read().
This allows reading acceleration data for all 3 axes at 16 kHz
sampling frequency using a 1MHz I2C bus frequency.

Signed-off-by: Francesco Lavra <flavra@baylibre.com>
---
 drivers/iio/accel/adxl380.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/drivers/iio/accel/adxl380.c b/drivers/iio/accel/adxl380.c
index 650cdbffd4a7..e3e6b182eb3d 100644
--- a/drivers/iio/accel/adxl380.c
+++ b/drivers/iio/accel/adxl380.c
@@ -965,14 +965,12 @@ static irqreturn_t adxl380_irq_handler(int irq, void  *p)
 		return IRQ_HANDLED;
 
 	fifo_entries = rounddown(fifo_entries, st->fifo_set_size);
-	for (i = 0; i < fifo_entries; i += st->fifo_set_size) {
-		ret = regmap_noinc_read(st->regmap, ADXL380_FIFO_DATA,
-					&st->fifo_buf[i],
-					2 * st->fifo_set_size);
-		if (ret)
-			return IRQ_HANDLED;
+	ret = regmap_noinc_read(st->regmap, ADXL380_FIFO_DATA, &st->fifo_buf,
+				sizeof(*st->fifo_buf) * fifo_entries);
+	if (ret)
+		return IRQ_HANDLED;
+	for (i = 0; i < fifo_entries; i += st->fifo_set_size)
 		iio_push_to_buffers(indio_dev, &st->fifo_buf[i]);
-	}
 
 	return IRQ_HANDLED;
 }
-- 
2.39.5

Re: [PATCH v2 2/2] iio: accel: adxl380: Optimize reading of FIFO entries in interrupt handler

[Jonathan Cameron]

On Mon, 19 Jan 2026 11:23:17 +0100
Francesco Lavra <flavra@baylibre.com> wrote:

> In order to minimize the time required for transferring FIFO data from the
> sensor to the host machine, perform the read from the FIFO in a single call
> to regmap_bulk_read().
It's a call to regmap_noinc_read()  not regmap_bulk_read()
I'll fix it.

> This allows reading acceleration data for all 3 axes at 16 kHz
> sampling frequency using a 1MHz I2C bus frequency.
> 
> Signed-off-by: Francesco Lavra <flavra@baylibre.com>
> ---
>  drivers/iio/accel/adxl380.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iio/accel/adxl380.c b/drivers/iio/accel/adxl380.c
> index 650cdbffd4a7..e3e6b182eb3d 100644
> --- a/drivers/iio/accel/adxl380.c
> +++ b/drivers/iio/accel/adxl380.c
> @@ -965,14 +965,12 @@ static irqreturn_t adxl380_irq_handler(int irq, void  *p)
>  		return IRQ_HANDLED;
>  
>  	fifo_entries = rounddown(fifo_entries, st->fifo_set_size);
> -	for (i = 0; i < fifo_entries; i += st->fifo_set_size) {
> -		ret = regmap_noinc_read(st->regmap, ADXL380_FIFO_DATA,
> -					&st->fifo_buf[i],
> -					2 * st->fifo_set_size);
> -		if (ret)
> -			return IRQ_HANDLED;
> +	ret = regmap_noinc_read(st->regmap, ADXL380_FIFO_DATA, &st->fifo_buf,
> +				sizeof(*st->fifo_buf) * fifo_entries);
> +	if (ret)
> +		return IRQ_HANDLED;
> +	for (i = 0; i < fifo_entries; i += st->fifo_set_size)
>  		iio_push_to_buffers(indio_dev, &st->fifo_buf[i]);
> -	}
>  
>  	return IRQ_HANDLED;
>  }

Re: [PATCH v2 2/2] iio: accel: adxl380: Optimize reading of FIFO entries in interrupt handler

[Andy Shevchenko]

On Thu, Jan 22, 2026 at 07:53:13PM +0000, Jonathan Cameron wrote:
> On Mon, 19 Jan 2026 11:23:17 +0100
> Francesco Lavra <flavra@baylibre.com> wrote:
> 
> > In order to minimize the time required for transferring FIFO data from the
> > sensor to the host machine, perform the read from the FIFO in a single call
> > to regmap_bulk_read().

> It's a call to regmap_noinc_read()  not regmap_bulk_read()
> I'll fix it.

This is interesting, does it mean the patch was never tested on the real HW?
Or maybe noninc is intentional?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2 2/2] iio: accel: adxl380: Optimize reading of FIFO entries in interrupt handler

[Jonathan Cameron]

On Fri, 23 Jan 2026 10:13:16 +0200
Andy Shevchenko <andriy.shevchenko@intel.com> wrote:

> On Thu, Jan 22, 2026 at 07:53:13PM +0000, Jonathan Cameron wrote:
> > On Mon, 19 Jan 2026 11:23:17 +0100
> > Francesco Lavra <flavra@baylibre.com> wrote:
> >   
> > > In order to minimize the time required for transferring FIFO data from the
> > > sensor to the host machine, perform the read from the FIFO in a single call
> > > to regmap_bulk_read().  
> 
> > It's a call to regmap_noinc_read()  not regmap_bulk_read()
> > I'll fix it.  
> 
> This is interesting, does it mean the patch was never tested on the real HW?
> Or maybe noninc is intentional?
> 
It's absolutely intentional.  The device presents a single register address
that has the fifo behind it (which is what we added noinc for years ago).
So patch should definitely work.  Goes from reading that register N times in
each call within a loop of M to reading it N x M.

If regcache is in use this makes a difference as avoids corrupting registers
after this point as the address increment expected in the hardware for
a bulk read doesn't happen.  Without regcache it's just "documentation" as
at least for protocols used here its the same as a bulk read on the bus.

So patch is fine, it just mentioned the wrong call in the description
I'd guess this is because someone is working with a tree that has the wrong call in
it but might be wrong.

Jonathan

Re: [PATCH v2 2/2] iio: accel: adxl380: Optimize reading of FIFO entries in interrupt handler

[Francesco Lavra]

On Fri, 2026-01-23 at 09:54 +0000, Jonathan Cameron wrote:
> On Fri, 23 Jan 2026 10:13:16 +0200
> Andy Shevchenko <andriy.shevchenko@intel.com> wrote:
> 
> > On Thu, Jan 22, 2026 at 07:53:13PM +0000, Jonathan Cameron wrote:
> > > On Mon, 19 Jan 2026 11:23:17 +0100
> > > Francesco Lavra <flavra@baylibre.com> wrote:
> > >   
> > > > In order to minimize the time required for transferring FIFO data
> > > > from the
> > > > sensor to the host machine, perform the read from the FIFO in a
> > > > single call
> > > > to regmap_bulk_read().  
> > 
> > > It's a call to regmap_noinc_read()  not regmap_bulk_read()
> > > I'll fix it.  
> > 
> > This is interesting, does it mean the patch was never tested on the
> > real HW?

The driver has been tested (by me) on real hardware, both before and after
this patch.

> > Or maybe noninc is intentional?
> > 
> It's absolutely intentional.  The device presents a single register
> address
> that has the fifo behind it (which is what we added noinc for years ago).
> So patch should definitely work.  Goes from reading that register N times
> in
> each call within a loop of M to reading it N x M.
> 
> If regcache is in use this makes a difference as avoids corrupting
> registers
> after this point as the address increment expected in the hardware for
> a bulk read doesn't happen.  Without regcache it's just "documentation"
> as
> at least for protocols used here its the same as a bulk read on the bus.
> 
> So patch is fine, it just mentioned the wrong call in the description
> I'd guess this is because someone is working with a tree that has the
> wrong call in
> it but might be wrong.

I have this patch applied also to older kernel versions where
regmap_noinc_read() doesn't exist, so this is just a copy-paste error in
the commit message. Sorry about that.

Re: [PATCH v2 2/2] iio: accel: adxl380: Optimize reading of FIFO entries in interrupt handler

[Andy Shevchenko]

On Fri, Jan 23, 2026 at 12:09:36PM +0100, Francesco Lavra wrote:
> On Fri, 2026-01-23 at 09:54 +0000, Jonathan Cameron wrote:
> > On Fri, 23 Jan 2026 10:13:16 +0200
> > Andy Shevchenko <andriy.shevchenko@intel.com> wrote:
> > > On Thu, Jan 22, 2026 at 07:53:13PM +0000, Jonathan Cameron wrote:
> > > > On Mon, 19 Jan 2026 11:23:17 +0100
> > > > Francesco Lavra <flavra@baylibre.com> wrote:
> > > >   
> > > > > In order to minimize the time required for transferring FIFO data
> > > > > from the
> > > > > sensor to the host machine, perform the read from the FIFO in a
> > > > > single call
> > > > > to regmap_bulk_read().  
> > > 
> > > > It's a call to regmap_noinc_read()  not regmap_bulk_read()
> > > > I'll fix it.  
> > > 
> > > This is interesting, does it mean the patch was never tested on the
> > > real HW?
> 
> The driver has been tested (by me) on real hardware, both before and after
> this patch.
> 
> > > Or maybe noninc is intentional?
> > > 
> > It's absolutely intentional.  The device presents a single register
> > address
> > that has the fifo behind it (which is what we added noinc for years ago).
> > So patch should definitely work.  Goes from reading that register N times
> > in
> > each call within a loop of M to reading it N x M.
> > 
> > If regcache is in use this makes a difference as avoids corrupting
> > registers
> > after this point as the address increment expected in the hardware for
> > a bulk read doesn't happen.  Without regcache it's just "documentation"
> > as
> > at least for protocols used here its the same as a bulk read on the bus.
> > 
> > So patch is fine, it just mentioned the wrong call in the description
> > I'd guess this is because someone is working with a tree that has the
> > wrong call in
> > it but might be wrong.
> 
> I have this patch applied also to older kernel versions where
> regmap_noinc_read() doesn't exist, so this is just a copy-paste error in
> the commit message. Sorry about that.

Thanks for clarifying this!

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2 0/2] accel: adxl380: Improve data reading from FIFO

[Jonathan Cameron]

On Mon, 19 Jan 2026 11:23:15 +0100
Francesco Lavra <flavra@baylibre.com> wrote:

> Patch 1 fixes a bug that might cause the adxl380 interrupt handler
> to read from the sensor FIFO more entries than actually present.
> Patch 2 optimizes transfer of FIFO data by minimizing transport protocol
> overhead.
> 
> Changes from v1 [1]:
> - replaced 2 with sizeof(*st->fifo_buf) in adxl380_irq_handler (Jonathan)
> 
> [1] https://lore.kernel.org/linux-iio/20260106193627.3989930-1-flavra@baylibre.com/T/
Series applied.

Given timing I've queued it up on the testing (soon to be togreg) branch of iio.git
but marked the first patch for stable so that it'll get backported after the merge
window.

Thanks,

Jonathan

> 
> Francesco Lavra (2):
>   iio: accel: adxl380: Avoid reading more entries than present in FIFO
>   iio: accel: adxl380: Optimize reading of FIFO entries in interrupt
>     handler
> 
>  drivers/iio/accel/adxl380.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
>