[PATCH] i2c: cadence: Implement timeout

[PATCH] i2c: cadence: Implement timeout

[shubhrajyoti.datta]

From: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>

In some cases we are waiting in a loop. Replace the infinite wait with
the  timeout.

Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
---
 drivers/i2c/busses/i2c-cadence.c | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
index b136057..9c38278 100644
--- a/drivers/i2c/busses/i2c-cadence.c
+++ b/drivers/i2c/busses/i2c-cadence.c
@@ -209,6 +209,7 @@ static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
 	struct cdns_i2c *id = ptr;
 	/* Signal completion only after everything is updated */
 	int done_flag = 0;
+	unsigned int timeout;
 	irqreturn_t status = IRQ_NONE;
 
 	isr_status = cdns_i2c_readreg(CDNS_I2C_ISR_OFFSET);
@@ -235,6 +236,7 @@ static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
 	    ((isr_status & CDNS_I2C_IXR_COMP) ||
 	     (isr_status & CDNS_I2C_IXR_DATA))) {
 		/* Read data if receive data valid is set */
+		timeout = 1000;
 		while (cdns_i2c_readreg(CDNS_I2C_SR_OFFSET) &
 		       CDNS_I2C_SR_RXDV) {
 			/*
@@ -253,6 +255,16 @@ static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
 
 			if (cdns_is_holdquirk(id, hold_quirk))
 				break;
+			timeout--;
+			if (timeout)
+				mdelay(1);
+			else
+				break;
+		}
+		if (!timeout) {
+			id->err_status = -ETIMEDOUT;
+			complete(&id->xfer_done);
+			return IRQ_HANDLED;
 		}
 
 		/*
@@ -262,12 +274,22 @@ static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
 		 * maintain transfer size non-zero while performing a large
 		 * receive operation.
 		 */
+		timeout = 1000;
 		if (cdns_is_holdquirk(id, hold_quirk)) {
 			/* wait while fifo is full */
-			while (cdns_i2c_readreg(CDNS_I2C_XFER_SIZE_OFFSET) !=
-			       (id->curr_recv_count - CDNS_I2C_FIFO_DEPTH))
-				;
-
+			while ((cdns_i2c_readreg(CDNS_I2C_XFER_SIZE_OFFSET) !=
+			       (id->curr_recv_count - CDNS_I2C_FIFO_DEPTH))) {
+				timeout--;
+				if (timeout)
+					mdelay(1);
+				else
+					break;
+			}
+			if (!timeout) {
+				id->err_status = -ETIMEDOUT;
+				complete(&id->xfer_done);
+				return IRQ_HANDLED;
+			}
 			/*
 			 * Check number of bytes to be received against maximum
 			 * transfer size and update register accordingly.
-- 
2.1.1

Re: [PATCH] i2c: cadence: Implement timeout

[Russell King - ARM Linux]

On Wed, Oct 24, 2018 at 04:20:03PM +0530, shubhrajyoti.datta@gmail.com wrote:
> From: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
> 
> In some cases we are waiting in a loop. Replace the infinite wait with
> the  timeout.
> 
> Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
> ---
>  drivers/i2c/busses/i2c-cadence.c | 30 ++++++++++++++++++++++++++----
>  1 file changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
> index b136057..9c38278 100644
> --- a/drivers/i2c/busses/i2c-cadence.c
> +++ b/drivers/i2c/busses/i2c-cadence.c
> @@ -209,6 +209,7 @@ static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
>  	struct cdns_i2c *id = ptr;
>  	/* Signal completion only after everything is updated */
>  	int done_flag = 0;
> +	unsigned int timeout;
>  	irqreturn_t status = IRQ_NONE;
>  
>  	isr_status = cdns_i2c_readreg(CDNS_I2C_ISR_OFFSET);
> @@ -235,6 +236,7 @@ static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
>  	    ((isr_status & CDNS_I2C_IXR_COMP) ||
>  	     (isr_status & CDNS_I2C_IXR_DATA))) {
>  		/* Read data if receive data valid is set */
> +		timeout = 1000;
>  		while (cdns_i2c_readreg(CDNS_I2C_SR_OFFSET) &
>  		       CDNS_I2C_SR_RXDV) {
>  			/*
> @@ -253,6 +255,16 @@ static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
>  
>  			if (cdns_is_holdquirk(id, hold_quirk))
>  				break;
> +			timeout--;
> +			if (timeout)
> +				mdelay(1);
> +			else
> +				break;
> +		}
> +		if (!timeout) {
> +			id->err_status = -ETIMEDOUT;
> +			complete(&id->xfer_done);
> +			return IRQ_HANDLED;

Good kernel programming principle: Always check for the success
condition when exiting due to timeout rather than the fact that we
timed out.

Also, is this _really_ a loop that needs a timeout condition?  Looking
at the original code, it looks like the purpose of the loop is to read
more than one byte, and you are introducing a 1ms delay between the
read of each byte.

-- 
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Re: [PATCH] i2c: cadence: Implement timeout

[Shubhrajyoti Datta]

On Wed, Oct 24, 2018 at 4:29 PM Russell King - ARM Linux
<linux@armlinux.org.uk> wrote:
>
> On Wed, Oct 24, 2018 at 04:20:03PM +0530, shubhrajyoti.datta@gmail.com wrote:
> > From: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
> >
> > In some cases we are waiting in a loop. Replace the infinite wait with
> > the  timeout.
> >
> > Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
> > ---
> >  drivers/i2c/busses/i2c-cadence.c | 30 ++++++++++++++++++++++++++----
> >  1 file changed, 26 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
> > index b136057..9c38278 100644
> > --- a/drivers/i2c/busses/i2c-cadence.c
> > +++ b/drivers/i2c/busses/i2c-cadence.c
> > @@ -209,6 +209,7 @@ static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
> >       struct cdns_i2c *id = ptr;
> >       /* Signal completion only after everything is updated */
> >       int done_flag = 0;
> > +     unsigned int timeout;
> >       irqreturn_t status = IRQ_NONE;
> >
> >       isr_status = cdns_i2c_readreg(CDNS_I2C_ISR_OFFSET);
> > @@ -235,6 +236,7 @@ static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
> >           ((isr_status & CDNS_I2C_IXR_COMP) ||
> >            (isr_status & CDNS_I2C_IXR_DATA))) {
> >               /* Read data if receive data valid is set */
> > +             timeout = 1000;
> >               while (cdns_i2c_readreg(CDNS_I2C_SR_OFFSET) &
> >                      CDNS_I2C_SR_RXDV) {
> >                       /*
> > @@ -253,6 +255,16 @@ static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
> >
> >                       if (cdns_is_holdquirk(id, hold_quirk))
> >                               break;
> > +                     timeout--;
> > +                     if (timeout)
> > +                             mdelay(1);
> > +                     else
> > +                             break;
> > +             }
> > +             if (!timeout) {
> > +                     id->err_status = -ETIMEDOUT;
> > +                     complete(&id->xfer_done);
> > +                     return IRQ_HANDLED;
>
> Good kernel programming principle: Always check for the success
> condition when exiting due to timeout rather than the fact that we
> timed out.
>
> Also, is this _really_ a loop that needs a timeout condition?  Looking
> at the original code, it looks like the purpose of the loop is to read
> more than one byte, and you are introducing a 1ms delay between the
> read of each byte.
Thanks for the review.
I agree will skip this patch.