linux-kernel - Re: [PATCH 2/4] i2c: pasemi: Improve error recovery

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Message-ID: <mp77oombs4xgr6sjj44ne7muybfrwejgehzv5xupeanh6udui3@ymgfesctindh>
Date: Thu, 20 Mar 2025 01:17:21 +0100
From: Andi Shyti <andi.shyti@...nel.org>
To: sven@...npeter.dev
Cc: Janne Grunau <j@...nau.net>, Alyssa Rosenzweig <alyssa@...enzweig.io>, 
	Madhavan Srinivasan <maddy@...ux.ibm.com>, Michael Ellerman <mpe@...erman.id.au>, 
	Nicholas Piggin <npiggin@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>, 
	Naveen N Rao <naveen@...nel.org>, linuxppc-dev@...ts.ozlabs.org, asahi@...ts.linux.dev, 
	linux-arm-kernel@...ts.infradead.org, linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Hector Martin <marcan@...can.st>
Subject: Re: [PATCH 2/4] i2c: pasemi: Improve error recovery

Hi Sven,

On Sat, Feb 22, 2025 at 01:38:34PM +0000, Sven Peter via B4 Relay wrote:
> The hardware (supposedly) has a 25ms timeout for clock stretching
> and the driver uses 100ms which should be plenty.

Can we add this lines as a comment to the define you are adding?

> The error
> reocvery itself is however lacking.

...

> -static void pasemi_smb_clear(struct pasemi_smbus *smbus)
> +static int pasemi_smb_clear(struct pasemi_smbus *smbus)
>  {
>  	unsigned int status;
> +	int timeout = TRANSFER_TIMEOUT_MS;
>  
>  	status = reg_read(smbus, REG_SMSTA);
> +
> +	/* First wait for the bus to go idle */
> +	while ((status & (SMSTA_XIP | SMSTA_JAM)) && timeout--) {
> +		msleep(1);

Please, use usleep_range for 1 millisecond timeout.

> +		status = reg_read(smbus, REG_SMSTA);
> +	}

You could use here readx_poll_timeout() here.

> +
> +	if (timeout < 0) {
> +		dev_warn(smbus->dev, "Bus is still stuck (status 0x%08x)\n", status);

if it's an error, please use an error.

> +		return -EIO;
> +	}
> +
> +	/* If any badness happened or there is data in the FIFOs, reset the FIFOs */
> +	if ((status & (SMSTA_MRNE | SMSTA_JMD | SMSTA_MTO | SMSTA_TOM | SMSTA_MTN | SMSTA_MTA)) ||
> +		!(status & SMSTA_MTE))

Please, fixe the alignment here.

> +		pasemi_reset(smbus);
> +
> +	/* Clear the flags */
>  	reg_write(smbus, REG_SMSTA, status);
> +
> +	return 0;
>  }
>  
>  static int pasemi_smb_waitready(struct pasemi_smbus *smbus)
>  {
> -	int timeout = 100;
> +	int timeout = TRANSFER_TIMEOUT_MS;
>  	unsigned int status;
>  
>  	if (smbus->use_irq) {
>  		reinit_completion(&smbus->irq_completion);
> -		reg_write(smbus, REG_IMASK, SMSTA_XEN | SMSTA_MTN);
> -		wait_for_completion_timeout(&smbus->irq_completion, msecs_to_jiffies(100));
> +		/* XEN should be set when a transaction terminates, whether due to error or not */
> +		reg_write(smbus, REG_IMASK, SMSTA_XEN);
> +		wait_for_completion_timeout(&smbus->irq_completion, msecs_to_jiffies(timeout));

what happens if the timeout expires?

>  		reg_write(smbus, REG_IMASK, 0);
>  		status = reg_read(smbus, REG_SMSTA);
>  	} else {

...

>  	struct pasemi_smbus *smbus = adapter->algo_data;
>  	int ret, i;
>  
> -	pasemi_smb_clear(smbus);
> +	if (pasemi_smb_clear(smbus))
> +		return -EIO;

Can we use

	ret = ...
	if (ret)
		return ret;

This way we return whatever comes from pasemi_smb_clear().

>  
>  	ret = 0;

This way we can remove this line, as well.

Andi