linux-kernel - Re: [PATCH v4 3/6] i2c: npcm: Modify timeout evaluation mechanism

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Message-ID: <z4g5alkk3cug7v5bsmrmzspgvo4hhu2ebtykht72ewwhsqxqgq@kg2tlpvz3ctp>
Date: Wed, 25 Sep 2024 22:24:25 +0200
From: Andi Shyti <andi.shyti@...nel.org>
To: warp5tw@...il.com
Cc: avifishman70@...il.com, tmaimon77@...il.com, tali.perry1@...il.com, 
	venture@...gle.com, yuenn@...gle.com, benjaminfair@...gle.com, 
	andriy.shevchenko@...ux.intel.com, wsa@...nel.org, rand.sec96@...il.com, 
	wsa+renesas@...g-engineering.com, tali.perry@...oton.com, Avi.Fishman@...oton.com, 
	tomer.maimon@...oton.com, KWLIU@...oton.com, JJLIU0@...oton.com, kfting@...oton.com, 
	openbmc@...ts.ozlabs.org, linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/6] i2c: npcm: Modify timeout evaluation mechanism

Hi Tyrone,

...

> diff --git a/drivers/i2c/busses/i2c-npcm7xx.c b/drivers/i2c/busses/i2c-npcm7xx.c
> index 2d034503d8bc..68f3d47323ab 100644
> --- a/drivers/i2c/busses/i2c-npcm7xx.c
> +++ b/drivers/i2c/busses/i2c-npcm7xx.c
> @@ -2132,19 +2132,12 @@ static int npcm_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
>  		}
>  	}
>  
> -	/*
> -	 * Adaptive TimeOut: estimated time in usec + 100% margin:
> -	 * 2: double the timeout for clock stretching case
> -	 * 9: bits per transaction (including the ack/nack)
> -	 */
> -	timeout_usec = (2 * 9 * USEC_PER_SEC / bus->bus_freq) * (2 + nread + nwrite);
> -	timeout = max_t(unsigned long, bus->adap.timeout, usecs_to_jiffies(timeout_usec));
>  	if (nwrite >= 32 * 1024 || nread >= 32 * 1024) {
>  		dev_err(bus->dev, "i2c%d buffer too big\n", bus->num);
>  		return -EINVAL;
>  	}
>  
> -	time_left = jiffies + timeout + 1;
> +	time_left = jiffies + bus->adap.timeout / bus->adap.retries + 1;
>  	do {
>  		/*
>  		 * we must clear slave address immediately when the bus is not
> @@ -2183,6 +2176,14 @@ static int npcm_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
>  	if (npcm_i2c_master_start_xmit(bus, slave_addr, nwrite, nread,
>  				       write_data, read_data, read_PEC,
>  				       read_block)) {
> +		/*
> +		 * Adaptive TimeOut: estimated time in usec + 100% margin:
> +		 * 2: double the timeout for clock stretching case
> +		 * 9: bits per transaction (including the ack/nack)
> +		 */
> +		timeout_usec = (2 * 9 * USEC_PER_SEC / bus->bus_freq) * (2 + nread + nwrite);
> +		timeout = max_t(unsigned long, bus->adap.timeout / bus->adap.retries,
> +				usecs_to_jiffies(timeout_usec));
>  		time_left = wait_for_completion_timeout(&bus->cmd_complete,
>  							timeout);
>  
> @@ -2308,7 +2309,7 @@ static int npcm_i2c_probe_bus(struct platform_device *pdev)
>  	adap = &bus->adap;
>  	adap->owner = THIS_MODULE;
>  	adap->retries = 3;
> -	adap->timeout = msecs_to_jiffies(35);
> +	adap->timeout = 2 * HZ;

Same here, I need some good description of why timeout is set to
2 seconds. If the datasheet says 35ms, I do not exclude that
someone in the future will send a patch saying "we don't need to
wait 2 seconds, wait 35ms as per datasheet".

Thanks,
Andi

>  	adap->algo = &npcm_i2c_algo;
>  	adap->quirks = &npcm_i2c_quirks;
>  	adap->algo_data = bus;
> -- 
> 2.34.1
>