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@xxxxxxxxx>
> > ---
> >   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