[PATCH] i2c: at91: Read all available bytes at once

[PATCH] i2c: at91: Read all available bytes at once

[David Engraf]

With FIFO enabled it is possible to read multiple bytes
at once in the interrupt handler as long as RXRDY is
set. This may also reduce the number of interrupts.

Signed-off-by: David Engraf <david.engraf@sysgo.com>
---
 drivers/i2c/busses/i2c-at91.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
index bfd1fdff64a9..d01c2b2384bd 100644
--- a/drivers/i2c/busses/i2c-at91.c
+++ b/drivers/i2c/busses/i2c-at91.c
@@ -518,8 +518,12 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id)
 	 * the RXRDY interrupt first in order to not keep garbage data in the
 	 * Receive Holding Register for the next transfer.
 	 */
-	if (irqstatus & AT91_TWI_RXRDY)
-		at91_twi_read_next_byte(dev);
+	if (irqstatus & AT91_TWI_RXRDY) {
+		/* read all available bytes at once when FIFO is used */
+		do {
+			at91_twi_read_next_byte(dev);
+		} while (at91_twi_read(dev, AT91_TWI_SR) & AT91_TWI_RXRDY);
+	}
 
 	/*
 	 * When a NACK condition is detected, the I2C controller sets the NACK,
-- 
2.14.1

Re: [PATCH] i2c: at91: Read all available bytes at once

[Ludovic Desroches]

Hi David,

On Wed, Apr 18, 2018 at 02:40:55PM +0200, David Engraf wrote:
> With FIFO enabled it is possible to read multiple bytes
> at once in the interrupt handler as long as RXRDY is
> set. This may also reduce the number of interrupts.
> 
> Signed-off-by: David Engraf <david.engraf@sysgo.com>
> ---
>  drivers/i2c/busses/i2c-at91.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
> index bfd1fdff64a9..d01c2b2384bd 100644
> --- a/drivers/i2c/busses/i2c-at91.c
> +++ b/drivers/i2c/busses/i2c-at91.c
> @@ -518,8 +518,12 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id)
>  	 * the RXRDY interrupt first in order to not keep garbage data in the
>  	 * Receive Holding Register for the next transfer.
>  	 */
> -	if (irqstatus & AT91_TWI_RXRDY)
> -		at91_twi_read_next_byte(dev);
> +	if (irqstatus & AT91_TWI_RXRDY) {
> +		/* read all available bytes at once when FIFO is used */
> +		do {
> +			at91_twi_read_next_byte(dev);
> +		} while (at91_twi_read(dev, AT91_TWI_SR) & AT91_TWI_RXRDY);

You can avoid this check by using the RXFL field to know the number of
data you can read. Did you try to use it? If yes, did you notice some issues?

Regards

Ludovic

> +	}
>  
>  	/*
>  	 * When a NACK condition is detected, the I2C controller sets the NACK,
> -- 
> 2.14.1
> 

Re: [PATCH] i2c: at91: Read all available bytes at once

[David Engraf]

Hi Ludovic,

Am 25.04.2018 um 17:08 schrieb Ludovic Desroches:
> Hi David,
> 
> On Wed, Apr 18, 2018 at 02:40:55PM +0200, David Engraf wrote:
>> With FIFO enabled it is possible to read multiple bytes
>> at once in the interrupt handler as long as RXRDY is
>> set. This may also reduce the number of interrupts.
>>
>> Signed-off-by: David Engraf <david.engraf@sysgo.com>
>> ---
>>   drivers/i2c/busses/i2c-at91.c | 8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
>> index bfd1fdff64a9..d01c2b2384bd 100644
>> --- a/drivers/i2c/busses/i2c-at91.c
>> +++ b/drivers/i2c/busses/i2c-at91.c
>> @@ -518,8 +518,12 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id)
>>   	 * the RXRDY interrupt first in order to not keep garbage data in the
>>   	 * Receive Holding Register for the next transfer.
>>   	 */
>> -	if (irqstatus & AT91_TWI_RXRDY)
>> -		at91_twi_read_next_byte(dev);
>> +	if (irqstatus & AT91_TWI_RXRDY) {
>> +		/* read all available bytes at once when FIFO is used */
>> +		do {
>> +			at91_twi_read_next_byte(dev);
>> +		} while (at91_twi_read(dev, AT91_TWI_SR) & AT91_TWI_RXRDY);
> 
> You can avoid this check by using the RXFL field to know the number of
> data you can read. Did you try to use it? If yes, did you notice some issues?

I did a quick test by reading RXFL and it worked as well but I decided 
to use the more readable solution by polling RXRDY. Also I don't need to 
check if the FIFO has been enabled.

If you prefer using RXFL I can create a new patch.

Best regards
- David


> Regards
> 
> Ludovic
> 
>> +	}
>>   
>>   	/*
>>   	 * When a NACK condition is detected, the I2C controller sets the NACK,
>> -- 
>> 2.14.1
>>

Re: [PATCH] i2c: at91: Read all available bytes at once

[Ludovic Desroches]

Hi David,

On Wed, Apr 25, 2018 at 05:43:09PM +0200, David Engraf wrote:
> Hi Ludovic,
> 
> Am 25.04.2018 um 17:08 schrieb Ludovic Desroches:
> > Hi David,
> > 
> > On Wed, Apr 18, 2018 at 02:40:55PM +0200, David Engraf wrote:
> > > With FIFO enabled it is possible to read multiple bytes
> > > at once in the interrupt handler as long as RXRDY is
> > > set. This may also reduce the number of interrupts.
> > > 
> > > Signed-off-by: David Engraf <david.engraf@sysgo.com>
> > > ---
> > >   drivers/i2c/busses/i2c-at91.c | 8 ++++++--
> > >   1 file changed, 6 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
> > > index bfd1fdff64a9..d01c2b2384bd 100644
> > > --- a/drivers/i2c/busses/i2c-at91.c
> > > +++ b/drivers/i2c/busses/i2c-at91.c
> > > @@ -518,8 +518,12 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id)
> > >   	 * the RXRDY interrupt first in order to not keep garbage data in the
> > >   	 * Receive Holding Register for the next transfer.
> > >   	 */
> > > -	if (irqstatus & AT91_TWI_RXRDY)
> > > -		at91_twi_read_next_byte(dev);
> > > +	if (irqstatus & AT91_TWI_RXRDY) {
> > > +		/* read all available bytes at once when FIFO is used */
> > > +		do {
> > > +			at91_twi_read_next_byte(dev);
> > > +		} while (at91_twi_read(dev, AT91_TWI_SR) & AT91_TWI_RXRDY);
> > 
> > You can avoid this check by using the RXFL field to know the number of
> > data you can read. Did you try to use it? If yes, did you notice some issues?
> 
> I did a quick test by reading RXFL and it worked as well but I decided to
> use the more readable solution by polling RXRDY. Also I don't need to check
> if the FIFO has been enabled.
> 
> If you prefer using RXFL I can create a new patch.

Honestly, I have no strong opinion about it. As you said you approach is
simple and easy to read.

About performances, I assume that both solutions are pretty the same for
small number of data. If the number increases, using the RXFL field
should give better results.

So I would say, maybe add a note in the commit log or in the code to
keep in mind there is this solution to go further.

Otherwise
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>

Regards

Ludovic

> 
> Best regards
> - David
> 
> 
> > Regards
> > 
> > Ludovic
> > 
> > > +	}
> > >   	/*
> > >   	 * When a NACK condition is detected, the I2C controller sets the NACK,
> > > -- 
> > > 2.14.1
> > > 
> 

[PATCH v2] i2c: at91: Read all available bytes at once

[David Engraf]

With FIFO enabled it is possible to read multiple bytes
at once in the interrupt handler as long as RXRDY is
set. This may also reduce the number of interrupts.

This patch polls RXRDY and reads all available bytes at
once.

Signed-off-by: David Engraf <david.engraf@sysgo.com>
---
 drivers/i2c/busses/i2c-at91.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
index bfd1fdff64a9..9caee5b79eac 100644
--- a/drivers/i2c/busses/i2c-at91.c
+++ b/drivers/i2c/busses/i2c-at91.c
@@ -518,8 +518,16 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id)
 	 * the RXRDY interrupt first in order to not keep garbage data in the
 	 * Receive Holding Register for the next transfer.
 	 */
-	if (irqstatus & AT91_TWI_RXRDY)
-		at91_twi_read_next_byte(dev);
+	if (irqstatus & AT91_TWI_RXRDY) {
+		/*
+		 * Read all available bytes at once by polling RXRDY usable w/ and w/o
+		 * FIFO. With FIFO enabled we could also read RXFL and avoid polling
+		 * RXRDY.
+		 */
+		do {
+			at91_twi_read_next_byte(dev);
+		} while (at91_twi_read(dev, AT91_TWI_SR) & AT91_TWI_RXRDY);
+	}
 
 	/*
 	 * When a NACK condition is detected, the I2C controller sets the NACK,
-- 
2.14.1

Re: [PATCH v2] i2c: at91: Read all available bytes at once

[Ludovic Desroches]

On Thu, Apr 26, 2018 at 11:53:14AM +0200, David Engraf wrote:
> With FIFO enabled it is possible to read multiple bytes
> at once in the interrupt handler as long as RXRDY is
> set. This may also reduce the number of interrupts.
> 
> This patch polls RXRDY and reads all available bytes at
> once.
> 
> Signed-off-by: David Engraf <david.engraf@sysgo.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>

Thanks a lot David.

Regards

Ludovic

> ---
>  drivers/i2c/busses/i2c-at91.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
> index bfd1fdff64a9..9caee5b79eac 100644
> --- a/drivers/i2c/busses/i2c-at91.c
> +++ b/drivers/i2c/busses/i2c-at91.c
> @@ -518,8 +518,16 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id)
>  	 * the RXRDY interrupt first in order to not keep garbage data in the
>  	 * Receive Holding Register for the next transfer.
>  	 */
> -	if (irqstatus & AT91_TWI_RXRDY)
> -		at91_twi_read_next_byte(dev);
> +	if (irqstatus & AT91_TWI_RXRDY) {
> +		/*
> +		 * Read all available bytes at once by polling RXRDY usable w/ and w/o
> +		 * FIFO. With FIFO enabled we could also read RXFL and avoid polling
> +		 * RXRDY.
> +		 */
> +		do {
> +			at91_twi_read_next_byte(dev);
> +		} while (at91_twi_read(dev, AT91_TWI_SR) & AT91_TWI_RXRDY);
> +	}
>  
>  	/*
>  	 * When a NACK condition is detected, the I2C controller sets the NACK,
> -- 
> 2.14.1
> 

Re: [PATCH v2] i2c: at91: Read all available bytes at once

[Wolfram Sang]

[-- Attachment #1: Type: text/plain, Size: 625 bytes --]

On Thu, Apr 26, 2018 at 11:53:14AM +0200, David Engraf wrote:
> With FIFO enabled it is possible to read multiple bytes
> at once in the interrupt handler as long as RXRDY is
> set. This may also reduce the number of interrupts.
> 
> This patch polls RXRDY and reads all available bytes at
> once.
> 
> Signed-off-by: David Engraf <david.engraf@sysgo.com>

checkpatch said twice:

WARNING: line over 80 characters

While I am not super-strict with this limit, it makes sense here IMO.
The comment stays readable, and we don't even lose a line.

Fixed it this time for you.

Applied to for-next, thanks!


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH v2] i2c: at91: Read all available bytes at once

[David Engraf]

Am 28.04.2018 um 14:38 schrieb Wolfram Sang:
> On Thu, Apr 26, 2018 at 11:53:14AM +0200, David Engraf wrote:
>> With FIFO enabled it is possible to read multiple bytes
>> at once in the interrupt handler as long as RXRDY is
>> set. This may also reduce the number of interrupts.
>>
>> This patch polls RXRDY and reads all available bytes at
>> once.
>>
>> Signed-off-by: David Engraf <david.engraf@sysgo.com>
> 
> checkpatch said twice:
> 
> WARNING: line over 80 characters
> 
> While I am not super-strict with this limit, it makes sense here IMO.
> The comment stays readable, and we don't even lose a line.

Sorry for that.

> Fixed it this time for you.

Thanks
- David

> Applied to for-next, thanks!
> 

Re: [PATCH] i2c: at91: Read all available bytes at once

[David Engraf]

Hi Ludovic,

Am 25.04.2018 um 17:08 schrieb Ludovic Desroches:
> Hi David,
> 
> On Wed, Apr 18, 2018 at 02:40:55PM +0200, David Engraf wrote:
>> With FIFO enabled it is possible to read multiple bytes
>> at once in the interrupt handler as long as RXRDY is
>> set. This may also reduce the number of interrupts.
>>
>> Signed-off-by: David Engraf <david.engraf@sysgo.com>
>> ---
>>   drivers/i2c/busses/i2c-at91.c | 8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
>> index bfd1fdff64a9..d01c2b2384bd 100644
>> --- a/drivers/i2c/busses/i2c-at91.c
>> +++ b/drivers/i2c/busses/i2c-at91.c
>> @@ -518,8 +518,12 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id)
>>   	 * the RXRDY interrupt first in order to not keep garbage data in the
>>   	 * Receive Holding Register for the next transfer.
>>   	 */
>> -	if (irqstatus & AT91_TWI_RXRDY)
>> -		at91_twi_read_next_byte(dev);
>> +	if (irqstatus & AT91_TWI_RXRDY) {
>> +		/* read all available bytes at once when FIFO is used */
>> +		do {
>> +			at91_twi_read_next_byte(dev);
>> +		} while (at91_twi_read(dev, AT91_TWI_SR) & AT91_TWI_RXRDY);
> 
> You can avoid this check by using the RXFL field to know the number of
> data you can read. Did you try to use it? If yes, did you notice some issues?

I did a quick test by reading RXFL and it worked as well but I decided 
to use the more readable solution by polling RXRDY. Also I don't need to 
check if the FIFO has been enabled.

If you prefer using RXFL I can create a new patch.

Best regards
- David


> Regards
> 
> Ludovic
> 
>> +	}
>>   
>>   	/*
>>   	 * When a NACK condition is detected, the I2C controller sets the NACK,
>> -- 
>> 2.14.1
>>

-- 
Mit freundlichen Grüßen/Best regards,

David Engraf
Product Engineer

SYSGO AG
Office Mainz
Am Pfaffenstein 14 / D-55270 Klein-Winternheim / Germany

Phone: +49-6136-9948-0 / Fax: +49-6136-9948-10
E-mail: david.engraf@sysgo.com
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