[PATCH 0/2] firmware: exynos-acpm: allow use during system shutdown

[PATCH 0/2] firmware: exynos-acpm: allow use during system shutdown

[André Draszik]

One user of this ACPM driver is a PMIC driver that needs to communicate
with the PMIC during late system shutdown and at that time we are not
allowed to sleep anymore.

This series address this by switching the code to using udelay() in the
specific case of system shutdown. This approach was inspired by I2C's
i2c_in_atomic_xfer_mode(), which has to deal with a similar corner
case.

Signed-off-by: André Draszik <andre.draszik@linaro.org>
---
André Draszik (2):
      firmware: exynos-acpm: use ktime APIs for timeout detection
      firmware: exynos-acpm: allow use during system shutdown

 drivers/firmware/samsung/exynos-acpm.c | 34 +++++++++++++++++++++++++---------
 1 file changed, 25 insertions(+), 9 deletions(-)
---
base-commit: c4d4884b67802c41fd67399747165d65c770621a
change-id: 20250321-acpm-atomic-033775b051ef

Best regards,
-- 
André Draszik <andre.draszik@linaro.org>

[PATCH 1/2] firmware: exynos-acpm: use ktime APIs for timeout detection

[André Draszik]

acpm_dequeue_by_polling() uses a loop counter and assumes that each
iteration of the loop takes 20us. It may take longer, though, because
usleep_range() may sleep a different amount.

Switch to using ktime_get() / ktime_after() to detect the timeout
condition more reliably.

This change also makes the code easier to follow and it allows us to
adjust the sleep without having to adjust the loop counter exit
condition. This will come in useful in a follow-up patch that changes
the delays.

Signed-off-by: André Draszik <andre.draszik@linaro.org>
---
 drivers/firmware/samsung/exynos-acpm.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/firmware/samsung/exynos-acpm.c b/drivers/firmware/samsung/exynos-acpm.c
index a85b2dbdd9f0d7b1f327f54a0a283e4f32587a98..d7ed6b77a957af5db5beba7deecce13ac7b30fd2 100644
--- a/drivers/firmware/samsung/exynos-acpm.c
+++ b/drivers/firmware/samsung/exynos-acpm.c
@@ -32,8 +32,7 @@
 
 #define ACPM_PROTOCOL_SEQNUM		GENMASK(21, 16)
 
-/* The unit of counter is 20 us. 5000 * 20 = 100 ms */
-#define ACPM_POLL_TIMEOUT		5000
+#define ACPM_POLL_TIMEOUT_US		(100 * USEC_PER_MSEC)
 #define ACPM_TX_TIMEOUT_US		500000
 
 #define ACPM_GS101_INITDATA_BASE	0xa000
@@ -284,12 +283,13 @@ static int acpm_dequeue_by_polling(struct acpm_chan *achan,
 				   const struct acpm_xfer *xfer)
 {
 	struct device *dev = achan->acpm->dev;
-	unsigned int cnt_20us = 0;
+	ktime_t timeout;
 	u32 seqnum;
 	int ret;
 
 	seqnum = FIELD_GET(ACPM_PROTOCOL_SEQNUM, xfer->txd[0]);
 
+	timeout = ktime_add_us(ktime_get(), ACPM_POLL_TIMEOUT_US);
 	do {
 		ret = acpm_get_rx(achan, xfer);
 		if (ret)
@@ -300,11 +300,10 @@ static int acpm_dequeue_by_polling(struct acpm_chan *achan,
 
 		/* Determined experimentally. */
 		usleep_range(20, 30);
-		cnt_20us++;
-	} while (cnt_20us < ACPM_POLL_TIMEOUT);
+	} while (!ktime_after(ktime_get(), timeout));
 
-	dev_err(dev, "Timeout! ch:%u s:%u bitmap:%lx, cnt_20us = %d.\n",
-		achan->id, seqnum, achan->bitmap_seqnum[0], cnt_20us);
+	dev_err(dev, "Timeout! ch:%u s:%u bitmap:%lx.\n",
+		achan->id, seqnum, achan->bitmap_seqnum[0]);
 
 	return -ETIME;
 }

-- 
2.49.0.395.g12beb8f557-goog

Re: [PATCH 1/2] firmware: exynos-acpm: use ktime APIs for timeout detection

[Tudor Ambarus]

On 3/21/25 4:40 PM, André Draszik wrote:
> acpm_dequeue_by_polling() uses a loop counter and assumes that each
> iteration of the loop takes 20us. It may take longer, though, because
> usleep_range() may sleep a different amount.
> 
> Switch to using ktime_get() / ktime_after() to detect the timeout
> condition more reliably.
> 
> This change also makes the code easier to follow and it allows us to
> adjust the sleep without having to adjust the loop counter exit
> condition. This will come in useful in a follow-up patch that changes
> the delays.
> 
> Signed-off-by: André Draszik <andre.draszik@linaro.org>
> ---
>  drivers/firmware/samsung/exynos-acpm.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/firmware/samsung/exynos-acpm.c b/drivers/firmware/samsung/exynos-acpm.c
> index a85b2dbdd9f0d7b1f327f54a0a283e4f32587a98..d7ed6b77a957af5db5beba7deecce13ac7b30fd2 100644
> --- a/drivers/firmware/samsung/exynos-acpm.c
> +++ b/drivers/firmware/samsung/exynos-acpm.c
> @@ -32,8 +32,7 @@
>  
>  #define ACPM_PROTOCOL_SEQNUM		GENMASK(21, 16)
>  
> -/* The unit of counter is 20 us. 5000 * 20 = 100 ms */
> -#define ACPM_POLL_TIMEOUT		5000
> +#define ACPM_POLL_TIMEOUT_US		(100 * USEC_PER_MSEC)
>  #define ACPM_TX_TIMEOUT_US		500000
>  
>  #define ACPM_GS101_INITDATA_BASE	0xa000
> @@ -284,12 +283,13 @@ static int acpm_dequeue_by_polling(struct acpm_chan *achan,
>  				   const struct acpm_xfer *xfer)
>  {
>  	struct device *dev = achan->acpm->dev;
> -	unsigned int cnt_20us = 0;
> +	ktime_t timeout;

#include <linux/ktime.h>

>  	u32 seqnum;
>  	int ret;
>  
>  	seqnum = FIELD_GET(ACPM_PROTOCOL_SEQNUM, xfer->txd[0]);
>  
> +	timeout = ktime_add_us(ktime_get(), ACPM_POLL_TIMEOUT_US);
>  	do {
>  		ret = acpm_get_rx(achan, xfer);
>  		if (ret)
> @@ -300,11 +300,10 @@ static int acpm_dequeue_by_polling(struct acpm_chan *achan,
>  
>  		/* Determined experimentally. */
>  		usleep_range(20, 30);
> -		cnt_20us++;
> -	} while (cnt_20us < ACPM_POLL_TIMEOUT);
> +	} while (!ktime_after(ktime_get(), timeout));

ktime_before()

With these addressed:
Reviewed-by: Tudor Ambarus <tudor.ambarus@linaro.org>

[PATCH 2/2] firmware: exynos-acpm: allow use during system shutdown

[André Draszik]

We need to access the PMIC during late system shutdown and at that time
we are not allowed to sleep anymore.

To make this case work, detect this condition and use busy waiting via
udelay() instead of usleep_range() in that situation.

The code isn't switched over to udelay() unconditionally so as to not
waste resources during normal operation. acpm_may_sleep() was heavily
inspired by the I2C subsystem's i2c_in_atomic_xfer_mode().

Signed-off-by: André Draszik <andre.draszik@linaro.org>

---
udelay(10) causes a checkpatch warning (it suggests to use
usleep_range() instead for usec >= 10), but that's exactly what we can
not do.
Reducing the udelay to be smaller will generally cause the loop to be
iterated more than once, which I wanted to avoid.
I could reflow the code to hide the actual value from checkpatch, e.g.
with the help of a local variable if that is preferred to ignoring the
checkpatch warning.
---
 drivers/firmware/samsung/exynos-acpm.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/samsung/exynos-acpm.c b/drivers/firmware/samsung/exynos-acpm.c
index d7ed6b77a957af5db5beba7deecce13ac7b30fd2..33cde6e88e2c0773fdd36c80927c77d3bcb44135 100644
--- a/drivers/firmware/samsung/exynos-acpm.c
+++ b/drivers/firmware/samsung/exynos-acpm.c
@@ -15,6 +15,8 @@
 #include <linux/firmware/samsung/exynos-acpm-protocol.h>
 #include <linux/io.h>
 #include <linux/iopoll.h>
+#include <linux/irqflags.h>
+#include <linux/kernel.h>
 #include <linux/mailbox/exynos-message.h>
 #include <linux/mailbox_client.h>
 #include <linux/module.h>
@@ -24,6 +26,7 @@
 #include <linux/of_address.h>
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
+#include <linux/preempt.h>
 #include <linux/slab.h>
 #include <linux/types.h>
 
@@ -272,6 +275,17 @@ static int acpm_get_rx(struct acpm_chan *achan, const struct acpm_xfer *xfer)
 	return 0;
 }
 
+/*
+ * When ACPM transfers happen very late, e.g. to access a PMIC when powering
+ * down, we can not sleep. We do want to sleep in the normal case, though, to
+ * avoid wasting CPU cycles!
+ */
+static bool acpm_may_sleep(void)
+{
+	return system_state <= SYSTEM_RUNNING ||
+		(IS_ENABLED(CONFIG_PREEMPT_COUNT) ? preemptible() : !irqs_disabled());
+}
+
 /**
  * acpm_dequeue_by_polling() - RX dequeue by polling.
  * @achan:	ACPM channel info.
@@ -299,7 +313,10 @@ static int acpm_dequeue_by_polling(struct acpm_chan *achan,
 			return 0;
 
 		/* Determined experimentally. */
-		usleep_range(20, 30);
+		if (!acpm_may_sleep())
+			udelay(10);
+		else
+			usleep_range(20, 30);
 	} while (!ktime_after(ktime_get(), timeout));
 
 	dev_err(dev, "Timeout! ch:%u s:%u bitmap:%lx.\n",

-- 
2.49.0.395.g12beb8f557-goog

Re: [PATCH 2/2] firmware: exynos-acpm: allow use during system shutdown

[Tudor Ambarus]

On 3/21/25 4:40 PM, André Draszik wrote:
> We need to access the PMIC during late system shutdown and at that time
> we are not allowed to sleep anymore.
> 
> To make this case work, detect this condition and use busy waiting via
> udelay() instead of usleep_range() in that situation.
> 
> The code isn't switched over to udelay() unconditionally so as to not
> waste resources during normal operation. acpm_may_sleep() was heavily
> inspired by the I2C subsystem's i2c_in_atomic_xfer_mode().
> 
> Signed-off-by: André Draszik <andre.draszik@linaro.org>

Reviewed-by: Tudor Ambarus <tudor.ambarus@linaro.org>
> 
> ---
> udelay(10) causes a checkpatch warning (it suggests to use
> usleep_range() instead for usec >= 10), but that's exactly what we can
> not do.
> Reducing the udelay to be smaller will generally cause the loop to be
> iterated more than once, which I wanted to avoid.
> I could reflow the code to hide the actual value from checkpatch, e.g.
> with the help of a local variable if that is preferred to ignoring the
> checkpatch warning.
> ---
>  drivers/firmware/samsung/exynos-acpm.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/samsung/exynos-acpm.c b/drivers/firmware/samsung/exynos-acpm.c
> index d7ed6b77a957af5db5beba7deecce13ac7b30fd2..33cde6e88e2c0773fdd36c80927c77d3bcb44135 100644
> --- a/drivers/firmware/samsung/exynos-acpm.c
> +++ b/drivers/firmware/samsung/exynos-acpm.c
> @@ -15,6 +15,8 @@
>  #include <linux/firmware/samsung/exynos-acpm-protocol.h>
>  #include <linux/io.h>
>  #include <linux/iopoll.h>
> +#include <linux/irqflags.h>
> +#include <linux/kernel.h>
>  #include <linux/mailbox/exynos-message.h>
>  #include <linux/mailbox_client.h>
>  #include <linux/module.h>
> @@ -24,6 +26,7 @@
>  #include <linux/of_address.h>
>  #include <linux/of_platform.h>
>  #include <linux/platform_device.h>
> +#include <linux/preempt.h>
>  #include <linux/slab.h>
>  #include <linux/types.h>
>  
> @@ -272,6 +275,17 @@ static int acpm_get_rx(struct acpm_chan *achan, const struct acpm_xfer *xfer)
>  	return 0;
>  }
>  
> +/*
> + * When ACPM transfers happen very late, e.g. to access a PMIC when powering
> + * down, we can not sleep. We do want to sleep in the normal case, though, to
> + * avoid wasting CPU cycles!
> + */
> +static bool acpm_may_sleep(void)
> +{
> +	return system_state <= SYSTEM_RUNNING ||
> +		(IS_ENABLED(CONFIG_PREEMPT_COUNT) ? preemptible() : !irqs_disabled());
> +}
> +
>  /**
>   * acpm_dequeue_by_polling() - RX dequeue by polling.
>   * @achan:	ACPM channel info.
> @@ -299,7 +313,10 @@ static int acpm_dequeue_by_polling(struct acpm_chan *achan,
>  			return 0;
>  
>  		/* Determined experimentally. */
> -		usleep_range(20, 30);
> +		if (!acpm_may_sleep())
> +			udelay(10);
> +		else
> +			usleep_range(20, 30);
>  	} while (!ktime_after(ktime_get(), timeout));
>  
>  	dev_err(dev, "Timeout! ch:%u s:%u bitmap:%lx.\n",
>