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

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Message-ID: <cab9e509-a506-5852-6b0d-ed3e4751eeb6@sysgo.com>
Date:   Wed, 25 Apr 2018 17:43:09 +0200
From:   David Engraf <david.engraf@...go.com>
To:     nicolas.ferre@...rochip.com, alexandre.belloni@...tlin.com,
        linux-i2c@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: at91: Read all available bytes at once

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@...go.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
>>