[PATCH v2 0/1] i2c: i2c-xiic: fix clearing of bnb irq

[PATCH v2 0/1] i2c: i2c-xiic: fix clearing of bnb irq

[Thilo Zirnstein]

Dear all,

This patch fixes the clearing routine for the bus not busy (bnb) irq.
The bnb is used to indicate that the current transfer is done.
A high level view of the software flow for tx:

* init i2c controller
* prepare all registers ( fill fifo, enable irqs, ... )
* start i2c txfer
* clear and enable bnb
* wait for completion
* ( serve interrupts )
* ( bnb interrupt ): complete completion

The datasheet ( pg090-axi-iic, Interrupt-Status-Register ISR)
states that the bnb bit can only be cleared if
the bus busy bit in the status register is set.
So the iic controller must have recognized that their is some activity
on the bus. ( Start condition )

Currently the bnb bit is cleared without checking or waiting for this
condition. This can lead to spurious bnb interrupts.

I am kind of unsure which branch to use for handing in my patch, 
this one is based i2c/i2c-fixes. 

Kind regards, 

Thilo Zirnstein
---

Changes in v2: 
- Unintentional changes removed .

Thilo Zirnstein (1):
  i2c: i2c-xiic: fix clearing of bnb irq

 drivers/i2c/busses/i2c-xiic.c | 42 +++++++++++++++++++++++++++--------
 1 file changed, 33 insertions(+), 9 deletions(-)

-- 
2.43.0

[PATCH v2 1/1] i2c: i2c-xiic: fix clearing of bnb irq

[Thilo Zirnstein]

Add a function for clearing the bnb bit,
It waits for all preconditions before clearing the bnb bit or times out.

Tested on Zynqmp dev board with some custom logic.
Tested-by: Thilo Zirnstein <thi.zirnstein@gmail.com>

Signed-off-by: Thilo Zirnstein <thi.zirnstein@gmail.com>
---
 drivers/i2c/busses/i2c-xiic.c | 42 +++++++++++++++++++++++++++--------
 1 file changed, 33 insertions(+), 9 deletions(-)

diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
index 5e397a7e63f6..da9cedb86f94 100644
--- a/drivers/i2c/busses/i2c-xiic.c
+++ b/drivers/i2c/busses/i2c-xiic.c
@@ -230,7 +230,9 @@ static const struct timing_regs timing_reg_values[] = {
 
 #define XIIC_RESET_MASK             0xAUL
 
-#define XIIC_PM_TIMEOUT		1000	/* ms */
+#define XIIC_PM_TIMEOUT 1000 /* ms */
+/* timeout waiting for bus busy */
+#define XIIC_BB_TIMEOUT		(msecs_to_jiffies(1))
 /* timeout waiting for the controller to respond */
 #define XIIC_I2C_TIMEOUT	(msecs_to_jiffies(1000))
 /* timeout waiting for the controller finish transfers */
@@ -392,6 +394,30 @@ static int xiic_wait_tx_empty(struct xiic_i2c *i2c)
 	return 0;
 }
 
+static int xiic_clear_en_bnb(struct xiic_i2c *i2c)
+{
+	u8 sr = 0, isr = 0;
+	unsigned long timeout;
+
+	timeout = jiffies + XIIC_BB_TIMEOUT;
+	for (isr = xiic_getreg8(i2c, XIIC_IISR_OFFSET);
+		(isr & XIIC_INTR_BNB_MASK);
+		isr = xiic_getreg8(i2c, XIIC_IISR_OFFSET)) {
+
+		sr = xiic_getreg8(i2c, XIIC_SR_REG_OFFSET);
+		if (sr & XIIC_SR_BUS_BUSY_MASK)
+			xiic_setreg8(i2c, XIIC_IISR_OFFSET, XIIC_INTR_BNB_MASK);
+
+		if (time_after(jiffies, timeout)) {
+			dev_err(i2c->dev, "Failed to clear bnb\n");
+			return -ETIMEDOUT;
+		}
+	}
+
+	xiic_irq_en(i2c, XIIC_INTR_BNB_MASK);
+	return 0;
+}
+
 /**
  * xiic_setclk - Sets the configured clock rate
  * @i2c: Pointer to the xiic device structure
@@ -881,9 +907,6 @@ static irqreturn_t xiic_process(int irq, void *dev_id)
 	}
 
 	if (pend & XIIC_INTR_BNB_MASK) {
-		/* IIC bus has transitioned to not busy */
-		clr |= XIIC_INTR_BNB_MASK;
-
 		/* The bus is not busy, disable BusNotBusy interrupt */
 		xiic_irq_dis(i2c, XIIC_INTR_BNB_MASK);
 
@@ -1028,7 +1051,7 @@ static void xiic_start_recv(struct xiic_i2c *i2c)
 
 		xiic_setreg16(i2c, XIIC_DTR_REG_OFFSET, val);
 
-		xiic_irq_clr_en(i2c, XIIC_INTR_BNB_MASK);
+		xiic_clear_en_bnb(i2c);
 	} else {
 		/*
 		 * If previous message is Tx, make sure that Tx FIFO is empty
@@ -1095,7 +1118,7 @@ static void xiic_start_recv(struct xiic_i2c *i2c)
 
 	if (i2c->nmsgs == 1)
 		/* very last, enable bus not busy as well */
-		xiic_irq_clr_en(i2c, XIIC_INTR_BNB_MASK);
+		xiic_clear_en_bnb(i2c);
 
 	/* the message is tx:ed */
 	i2c->tx_pos = msg->len;
@@ -1179,11 +1202,11 @@ static void xiic_start_send(struct xiic_i2c *i2c)
 		/* Clear any pending Tx empty, Tx Error and then enable them */
 		xiic_irq_clr_en(i2c, XIIC_INTR_TX_EMPTY_MASK |
 				XIIC_INTR_TX_ERROR_MASK |
-				XIIC_INTR_BNB_MASK |
 				((i2c->nmsgs > 1 || xiic_tx_space(i2c)) ?
 				XIIC_INTR_TX_HALF_MASK : 0));
 
 		xiic_fill_tx_fifo(i2c);
+		xiic_clear_en_bnb(i2c);
 	} else {
 		/*
 		 * If previous message is Tx, make sure that Tx FIFO is empty
@@ -1225,8 +1248,9 @@ static void xiic_start_send(struct xiic_i2c *i2c)
 
 		/* Clear any pending Tx empty, Tx Error and then enable them */
 		xiic_irq_clr_en(i2c, XIIC_INTR_TX_EMPTY_MASK |
-				XIIC_INTR_TX_ERROR_MASK |
-				XIIC_INTR_BNB_MASK);
+						XIIC_INTR_TX_ERROR_MASK);
+
+		xiic_clear_en_bnb(i2c);
 	}
 
 	i2c->prev_msg_tx = true;
-- 
2.43.0

Re: [PATCH v2 1/1] i2c: i2c-xiic: fix clearing of bnb irq

[Andi Shyti]

Hi Thilo,

On Thu, Oct 15, 2026 at 10:11:27AM +0200, Thilo Zirnstein wrote:
> Add a function for clearing the bnb bit,
> It waits for all preconditions before clearing the bnb bit or times out.
> 
> Tested on Zynqmp dev board with some custom logic.
> Tested-by: Thilo Zirnstein <thi.zirnstein@gmail.com>
> 

Please, don't leave blank lines between tags. Moreover in this
case I don't need your Tested-by, I believe you tested your patch
before sending.

> Signed-off-by: Thilo Zirnstein <thi.zirnstein@gmail.com>

I'd need here an ack from Michal.

> ---
>  drivers/i2c/busses/i2c-xiic.c | 42 +++++++++++++++++++++++++++--------
>  1 file changed, 33 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
> index 5e397a7e63f6..da9cedb86f94 100644
> --- a/drivers/i2c/busses/i2c-xiic.c
> +++ b/drivers/i2c/busses/i2c-xiic.c
> @@ -230,7 +230,9 @@ static const struct timing_regs timing_reg_values[] = {
>  
>  #define XIIC_RESET_MASK             0xAUL
>  
> -#define XIIC_PM_TIMEOUT		1000	/* ms */
> +#define XIIC_PM_TIMEOUT 1000 /* ms */

Why this change?

> +/* timeout waiting for bus busy */
> +#define XIIC_BB_TIMEOUT		(msecs_to_jiffies(1))

I don't see much benefit from this define as it's used only once.
It just makes it more difficult to read.

>  /* timeout waiting for the controller to respond */
>  #define XIIC_I2C_TIMEOUT	(msecs_to_jiffies(1000))
>  /* timeout waiting for the controller finish transfers */
> @@ -392,6 +394,30 @@ static int xiic_wait_tx_empty(struct xiic_i2c *i2c)
>  	return 0;
>  }
>  
> +static int xiic_clear_en_bnb(struct xiic_i2c *i2c)

Why do you need to return an error value if you ignore it
everywhere?

> +{
> +	u8 sr = 0, isr = 0;
> +	unsigned long timeout;
> +
> +	timeout = jiffies + XIIC_BB_TIMEOUT;
> +	for (isr = xiic_getreg8(i2c, XIIC_IISR_OFFSET);
> +		(isr & XIIC_INTR_BNB_MASK);
> +		isr = xiic_getreg8(i2c, XIIC_IISR_OFFSET)) {

this for loop is quite ugly. I believe that with a do...while()
you can write a clearer code.

> +
> +		sr = xiic_getreg8(i2c, XIIC_SR_REG_OFFSET);
> +		if (sr & XIIC_SR_BUS_BUSY_MASK)
> +			xiic_setreg8(i2c, XIIC_IISR_OFFSET, XIIC_INTR_BNB_MASK);
> +
> +		if (time_after(jiffies, timeout)) {

If this is called in a context where interrupts are disabled,
jiffies might not be incremented and you end up looping forever.
How about using read_poll_timeout_atomic() instead?

> +			dev_err(i2c->dev, "Failed to clear bnb\n");
> +			return -ETIMEDOUT;
> +		}
> +	}
> +
> +	xiic_irq_en(i2c, XIIC_INTR_BNB_MASK);
> +	return 0;
> +}
> +
>  /**
>   * xiic_setclk - Sets the configured clock rate
>   * @i2c: Pointer to the xiic device structure

...

> @@ -1225,8 +1248,9 @@ static void xiic_start_send(struct xiic_i2c *i2c)
>  
>  		/* Clear any pending Tx empty, Tx Error and then enable them */
>  		xiic_irq_clr_en(i2c, XIIC_INTR_TX_EMPTY_MASK |
> -				XIIC_INTR_TX_ERROR_MASK |
> -				XIIC_INTR_BNB_MASK);
> +						XIIC_INTR_TX_ERROR_MASK);
> +

this needs to be aligned properly.

Andi

> +		xiic_clear_en_bnb(i2c);
>  	}
>  
>  	i2c->prev_msg_tx = true;
> -- 
> 2.43.0
> 

Re: [PATCH v2 1/1] i2c: i2c-xiic: fix clearing of bnb irq

[Thilo Zirnstein]

Hi Andi, 

Thanks for your review and feedback.

On Fri, Oct 16, 2026 at 01:51:35AM +0200, Andi Shyti wrote:
> Hi Thilo,
> 
> On Thu, Oct 15, 2026 at 10:11:27AM +0200, Thilo Zirnstein wrote:
> > Add a function for clearing the bnb bit,
> > It waits for all preconditions before clearing the bnb bit or times out.
> > 
> > Tested on Zynqmp dev board with some custom logic.
> > Tested-by: Thilo Zirnstein <thi.zirnstein@gmail.com>
> > 
> 
> Please, don't leave blank lines between tags. Moreover in this
> case I don't need your Tested-by, I believe you tested your patch
> before sending.

Ack

> 
> > Signed-off-by: Thilo Zirnstein <thi.zirnstein@gmail.com>
> 
> I'd need here an ack from Michal.

Ok, but this is nothing i can steer somehow - right ? 

> 
> > ---
> >  drivers/i2c/busses/i2c-xiic.c | 42 +++++++++++++++++++++++++++--------
> >  1 file changed, 33 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
> > index 5e397a7e63f6..da9cedb86f94 100644
> > --- a/drivers/i2c/busses/i2c-xiic.c
> > +++ b/drivers/i2c/busses/i2c-xiic.c
> > @@ -230,7 +230,9 @@ static const struct timing_regs timing_reg_values[] = {
> >  
> >  #define XIIC_RESET_MASK             0xAUL
> >  
> > -#define XIIC_PM_TIMEOUT		1000	/* ms */
> > +#define XIIC_PM_TIMEOUT 1000 /* ms */
> 
> Why this change?

Unintentionally, :/ 

> 
> > +/* timeout waiting for bus busy */
> > +#define XIIC_BB_TIMEOUT		(msecs_to_jiffies(1))
> 
> I don't see much benefit from this define as it's used only once.
> It just makes it more difficult to read.

I think it is a question of personal preference,  
I prefer to read a meaningfull name instead of a "magical" number. 
The driver code has some other defines which are just used one time
( XIIC_PM_TIMEOUT, XIIC_XFER_TIMEOUT_US ), so it fits to the code base too. 

If you not insist, i keep it.

> 
> >  /* timeout waiting for the controller to respond */
> >  #define XIIC_I2C_TIMEOUT	(msecs_to_jiffies(1000))
> >  /* timeout waiting for the controller finish transfers */
> > @@ -392,6 +394,30 @@ static int xiic_wait_tx_empty(struct xiic_i2c *i2c)
> >  	return 0;
> >  }
> >  
> > +static int xiic_clear_en_bnb(struct xiic_i2c *i2c)
> 
> Why do you need to return an error value if you ignore it
> everywhere?
> 
> > +{
> > +	u8 sr = 0, isr = 0;
> > +	unsigned long timeout;
> > +
> > +	timeout = jiffies + XIIC_BB_TIMEOUT;
> > +	for (isr = xiic_getreg8(i2c, XIIC_IISR_OFFSET);
> > +		(isr & XIIC_INTR_BNB_MASK);
> > +		isr = xiic_getreg8(i2c, XIIC_IISR_OFFSET)) {
> 
> this for loop is quite ugly. I believe that with a do...while()
> you can write a clearer code.

Ack, I can get rid of this whole loop if using 
read_poll_timeout_atomic()
A readback after clearing the bit is not needed.

> 
> > +
> > +		sr = xiic_getreg8(i2c, XIIC_SR_REG_OFFSET);
> > +		if (sr & XIIC_SR_BUS_BUSY_MASK)
> > +			xiic_setreg8(i2c, XIIC_IISR_OFFSET, XIIC_INTR_BNB_MASK);
> > +
> > +		if (time_after(jiffies, timeout)) {
> 
> If this is called in a context where interrupts are disabled,
> jiffies might not be incremented and you end up looping forever.
> How about using read_poll_timeout_atomic() instead?

Ack, good catch, i will fix that.

> 
> > +			dev_err(i2c->dev, "Failed to clear bnb\n");
> > +			return -ETIMEDOUT;
> > +		}
> > +	}
> > +
> > +	xiic_irq_en(i2c, XIIC_INTR_BNB_MASK);
> > +	return 0;
> > +}
> > +
> >  /**
> >   * xiic_setclk - Sets the configured clock rate
> >   * @i2c: Pointer to the xiic device structure
> 
> ...
> 
> > @@ -1225,8 +1248,9 @@ static void xiic_start_send(struct xiic_i2c *i2c)
> >  
> >  		/* Clear any pending Tx empty, Tx Error and then enable them */
> >  		xiic_irq_clr_en(i2c, XIIC_INTR_TX_EMPTY_MASK |
> > -				XIIC_INTR_TX_ERROR_MASK |
> > -				XIIC_INTR_BNB_MASK);
> > +						XIIC_INTR_TX_ERROR_MASK);
> > +
> 
> this needs to be aligned properly.

Ack

> 
> Andi
> 
> > +		xiic_clear_en_bnb(i2c);
> >  	}
> >  
> >  	i2c->prev_msg_tx = true;
> > -- 
> > 2.43.0
> >

Kind regards,

Thilo

Re: [PATCH v2 1/1] i2c: i2c-xiic: fix clearing of bnb irq

[Michal Simek]

+Shubhrajyoti, Venkatesh

On 10/16/26 12:04, Thilo Zirnstein wrote:
> Hi Andi,
> 
> Thanks for your review and feedback.
> 
> On Fri, Oct 16, 2026 at 01:51:35AM +0200, Andi Shyti wrote:
>> Hi Thilo,
>>
>> On Thu, Oct 15, 2026 at 10:11:27AM +0200, Thilo Zirnstein wrote:
>>> Add a function for clearing the bnb bit,
>>> It waits for all preconditions before clearing the bnb bit or times out.
>>>
>>> Tested on Zynqmp dev board with some custom logic.
>>> Tested-by: Thilo Zirnstein <thi.zirnstein@gmail.com>
>>>
>>
>> Please, don't leave blank lines between tags. Moreover in this
>> case I don't need your Tested-by, I believe you tested your patch
>> before sending.
> 
> Ack
> 
>>
>>> Signed-off-by: Thilo Zirnstein <thi.zirnstein@gmail.com>
>>
>> I'd need here an ack from Michal.
> 
> Ok, but this is nothing i can steer somehow - right ?

Just give us some time to look at it.

Shubhrajyoti: Can you please look at the patch?

Venkatesh: Can you please test it on boards?

Thanks,
Michal