linux-kernel - Re: [PATCH] i2c: sprd: use a specific timeout to avoid system hang up issue

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Message-ID: <20201211145335.GC1990@kunai>
Date:   Fri, 11 Dec 2020 15:53:35 +0100
From:   Wolfram Sang <wsa@...nel.org>
To:     Chunyan Zhang <zhang.lyra@...il.com>
Cc:     Baolin Wang <baolin.wang7@...il.com>,
        Orson Zhai <orsonzhai@...il.com>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Chunyan Zhang <chunyan.zhang@...soc.com>,
        Linhua Xu <linhua.xu@...soc.com>
Subject: Re: [PATCH] i2c: sprd: use a specific timeout to avoid system hang
 up issue

Hi,

thanks for your patch!

> If the i2c device SCL bus being pulled up due to some exception before
> message transfer done, the system cannot receive the completing interrupt
> signal any more, it would not exit waiting loop until MAX_SCHEDULE_TIMEOUT
> jiffies eclipse, that would make the system seemed hang up. To avoid that
> happen, this patch adds a specific timeout for message transfer.

Yes.

> Fixes: 8b9ec0719834 ("i2c: Add Spreadtrum I2C controller driver")
> Original-by: Linhua Xu <linhua.xu@...soc.com>

I can't find this tag documented. Maybe "Co-developed by"? Or just
"Signed-off-by"?

> +	unsigned long timeout = msecs_to_jiffies(I2C_XFER_TIMEOUT);
>  
>  	i2c_dev->msg = msg;
>  	i2c_dev->buf = msg->buf;
> @@ -273,7 +276,9 @@ static int sprd_i2c_handle_msg(struct i2c_adapter *i2c_adap,
>  
>  	sprd_i2c_opt_start(i2c_dev);
>  
> -	wait_for_completion(&i2c_dev->complete);
> +	timeout = wait_for_completion_timeout(&i2c_dev->complete, timeout);
> +	if (!timeout)
> +		return -EIO;

Basically OK, but readability can be improved. Because it reads "if not
timeout, then return error". But it IS a timeout :) What about this:

	time_left = wait_for_completion_timeout(&i2c_dev->complete,
						msecs_to_jiffies(I2C_XFER_TIMEOUT));
	if (!time_left)
		...

and the rest adjusted accordingly. What do you think?

Kind regards,

   Wolfram


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