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[PATCH 2/6] i2c: spacemit: remove stop function to avoid bus error

Troy Mitchell posted 6 patches 5 months, 2 weeks ago
[PATCH 2/6] i2c: spacemit: remove stop function to avoid bus error
Posted by Troy Mitchell 5 months, 2 weeks ago 
Previously, STOP handling was split into two separate steps:
  1) clear TB/STOP/START/ACK bits
  2) issue STOP by calling spacemit_i2c_stop()

This left a small window where the control register was updated
twice, which can confuse the controller. While this race has not
been observed with interrupt-driven transfers, it reliably causes
bus errors in PIO mode.

Inline the STOP sequence into the IRQ handler and ensure that
control register bits are updated atomically in a single writel().

Fixes: 5ea558473fa31 ("i2c: spacemit: add support for SpacemiT K1 SoC")
Signed-off-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>
---
 drivers/i2c/busses/i2c-k1.c | 28 +++++++++-------------------
 1 file changed, 9 insertions(+), 19 deletions(-)

diff --git a/drivers/i2c/busses/i2c-k1.c b/drivers/i2c/busses/i2c-k1.c
index ee08811f4087c8e709d25dd314854ed643cc5a47..d342752030d077953adf84a2886211de96e843c4 100644
--- a/drivers/i2c/busses/i2c-k1.c
+++ b/drivers/i2c/busses/i2c-k1.c
@@ -267,19 +267,6 @@ static void spacemit_i2c_start(struct spacemit_i2c_dev *i2c)
 	writel(val, i2c->base + SPACEMIT_ICR);
 }
 
-static void spacemit_i2c_stop(struct spacemit_i2c_dev *i2c)
-{
-	u32 val;
-
-	val = readl(i2c->base + SPACEMIT_ICR);
-	val |= SPACEMIT_CR_STOP | SPACEMIT_CR_ALDIE | SPACEMIT_CR_TB;
-
-	if (i2c->read)
-		val |= SPACEMIT_CR_ACKNAK;
-
-	writel(val, i2c->base + SPACEMIT_ICR);
-}
-
 static int spacemit_i2c_xfer_msg(struct spacemit_i2c_dev *i2c)
 {
 	unsigned long time_left;
@@ -412,7 +399,6 @@ static irqreturn_t spacemit_i2c_irq_handler(int irq, void *devid)
 
 	val = readl(i2c->base + SPACEMIT_ICR);
 	val &= ~(SPACEMIT_CR_TB | SPACEMIT_CR_ACKNAK | SPACEMIT_CR_STOP | SPACEMIT_CR_START);
-	writel(val, i2c->base + SPACEMIT_ICR);
 
 	switch (i2c->state) {
 	case SPACEMIT_STATE_START:
@@ -429,14 +415,18 @@ static irqreturn_t spacemit_i2c_irq_handler(int irq, void *devid)
 	}
 
 	if (i2c->state != SPACEMIT_STATE_IDLE) {
+		val |= SPACEMIT_CR_TB;
+		if (i2c->is_pio)
+			val |= SPACEMIT_CR_ALDIE;
+
 		if (spacemit_i2c_is_last_msg(i2c)) {
 			/* trigger next byte with stop */
-			spacemit_i2c_stop(i2c);
-		} else {
-			/* trigger next byte */
-			val |= SPACEMIT_CR_ALDIE | SPACEMIT_CR_TB;
-			writel(val, i2c->base + SPACEMIT_ICR);
+			val |= SPACEMIT_CR_STOP;
+
+			if (i2c->read)
+				val |= SPACEMIT_CR_ACKNAK;
 		}
+		writel(val, i2c->base + SPACEMIT_ICR);
 	}
 
 err_out:

-- 
2.50.1
Re: [PATCH 2/6] i2c: spacemit: remove stop function to avoid bus error
Posted by Aurelien Jarno 4 months, 2 weeks ago 
On 2025-08-27 15:39, Troy Mitchell wrote:
> Previously, STOP handling was split into two separate steps:
>   1) clear TB/STOP/START/ACK bits
>   2) issue STOP by calling spacemit_i2c_stop()
> 
> This left a small window where the control register was updated
> twice, which can confuse the controller. While this race has not
> been observed with interrupt-driven transfers, it reliably causes
> bus errors in PIO mode.
> 
> Inline the STOP sequence into the IRQ handler and ensure that
> control register bits are updated atomically in a single writel().
> 
> Fixes: 5ea558473fa31 ("i2c: spacemit: add support for SpacemiT K1 SoC")
> Signed-off-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>
> ---
>  drivers/i2c/busses/i2c-k1.c | 28 +++++++++-------------------
>  1 file changed, 9 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-k1.c b/drivers/i2c/busses/i2c-k1.c
> index ee08811f4087c8e709d25dd314854ed643cc5a47..d342752030d077953adf84a2886211de96e843c4 100644
> --- a/drivers/i2c/busses/i2c-k1.c
> +++ b/drivers/i2c/busses/i2c-k1.c
> @@ -267,19 +267,6 @@ static void spacemit_i2c_start(struct spacemit_i2c_dev *i2c)
>  	writel(val, i2c->base + SPACEMIT_ICR);
>  }
>  
> -static void spacemit_i2c_stop(struct spacemit_i2c_dev *i2c)
> -{
> -	u32 val;
> -
> -	val = readl(i2c->base + SPACEMIT_ICR);
> -	val |= SPACEMIT_CR_STOP | SPACEMIT_CR_ALDIE | SPACEMIT_CR_TB;
> -
> -	if (i2c->read)
> -		val |= SPACEMIT_CR_ACKNAK;
> -
> -	writel(val, i2c->base + SPACEMIT_ICR);
> -}
> -
>  static int spacemit_i2c_xfer_msg(struct spacemit_i2c_dev *i2c)
>  {
>  	unsigned long time_left;
> @@ -412,7 +399,6 @@ static irqreturn_t spacemit_i2c_irq_handler(int irq, void *devid)
>  
>  	val = readl(i2c->base + SPACEMIT_ICR);
>  	val &= ~(SPACEMIT_CR_TB | SPACEMIT_CR_ACKNAK | SPACEMIT_CR_STOP | SPACEMIT_CR_START);
> -	writel(val, i2c->base + SPACEMIT_ICR);
>  
>  	switch (i2c->state) {
>  	case SPACEMIT_STATE_START:
> @@ -429,14 +415,18 @@ static irqreturn_t spacemit_i2c_irq_handler(int irq, void *devid)
>  	}
>  
>  	if (i2c->state != SPACEMIT_STATE_IDLE) {
> +		val |= SPACEMIT_CR_TB;
> +		if (i2c->is_pio)
> +			val |= SPACEMIT_CR_ALDIE;
> +

This needs to be moved to the last patch introducing PIO support.

>  		if (spacemit_i2c_is_last_msg(i2c)) {
>  			/* trigger next byte with stop */
> -			spacemit_i2c_stop(i2c);
> -		} else {
> -			/* trigger next byte */
> -			val |= SPACEMIT_CR_ALDIE | SPACEMIT_CR_TB;
> -			writel(val, i2c->base + SPACEMIT_ICR);
> +			val |= SPACEMIT_CR_STOP;
> +
> +			if (i2c->read)
> +				val |= SPACEMIT_CR_ACKNAK;
>  		}
> +		writel(val, i2c->base + SPACEMIT_ICR);
>  	}
>  
>  err_out:

Otherwise sounds good.

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                     http://aurel32.net
Re: [PATCH 2/6] i2c: spacemit: remove stop function to avoid bus error
Posted by Troy Mitchell 4 months, 2 weeks ago 
On Mon, Sep 22, 2025 at 10:55:57PM +0200, Aurelien Jarno wrote:
> On 2025-08-27 15:39, Troy Mitchell wrote:
> > Previously, STOP handling was split into two separate steps:
> >   1) clear TB/STOP/START/ACK bits
> >   2) issue STOP by calling spacemit_i2c_stop()
> > 
> > This left a small window where the control register was updated
> > twice, which can confuse the controller. While this race has not
> > been observed with interrupt-driven transfers, it reliably causes
> > bus errors in PIO mode.
> > 
> > Inline the STOP sequence into the IRQ handler and ensure that
> > control register bits are updated atomically in a single writel().
> > 
> > Fixes: 5ea558473fa31 ("i2c: spacemit: add support for SpacemiT K1 SoC")
> > Signed-off-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>
> > ---
> >  drivers/i2c/busses/i2c-k1.c | 28 +++++++++-------------------
> >  1 file changed, 9 insertions(+), 19 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-k1.c b/drivers/i2c/busses/i2c-k1.c
> > index ee08811f4087c8e709d25dd314854ed643cc5a47..d342752030d077953adf84a2886211de96e843c4 100644
> > --- a/drivers/i2c/busses/i2c-k1.c
> > +++ b/drivers/i2c/busses/i2c-k1.c
> > @@ -429,14 +415,18 @@ static irqreturn_t spacemit_i2c_irq_handler(int irq, void *devid)
> >  	}
> >  
> >  	if (i2c->state != SPACEMIT_STATE_IDLE) {
> > +		val |= SPACEMIT_CR_TB;
> > +		if (i2c->is_pio)
> > +			val |= SPACEMIT_CR_ALDIE;
> > +
> 
> This needs to be moved to the last patch introducing PIO support.
Nice catch!
I'll fix it and send v2 today.
> 
> >  		if (spacemit_i2c_is_last_msg(i2c)) {
> >  			/* trigger next byte with stop */
> > -			spacemit_i2c_stop(i2c);
> > -		} else {
> > -			/* trigger next byte */
> > -			val |= SPACEMIT_CR_ALDIE | SPACEMIT_CR_TB;
> > -			writel(val, i2c->base + SPACEMIT_ICR);
> > +			val |= SPACEMIT_CR_STOP;
> > +
> > +			if (i2c->read)
> > +				val |= SPACEMIT_CR_ACKNAK;
> >  		}
> > +		writel(val, i2c->base + SPACEMIT_ICR);
> >  	}
> >  
> >  err_out:
> 
> Otherwise sounds good.
> 
> -- 
> Aurelien Jarno                          GPG: 4096R/1DDD8C9B
> aurelien@aurel32.net                     http://aurel32.net
>

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