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

From: David Engraf
Date: Wed Apr 25 2018 - 11:43:16 EST

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



+ }
* When a NACK condition is detected, the I2C controller sets the NACK,