linux-kernel - Re: [PATCH 1/2] [i2c-bcm2835] Fully clean up hardware state machine after a timeout

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Message-ID: <dfda6779-6ac7-4d4c-b249-84780b30bd42@gmx.net>
Date:   Tue, 31 Oct 2023 13:36:18 +0100
From:   Stefan Wahren <wahrenst@....net>
To:     mike.isely@...altdigital.com, Andi Shyti <andi.shyti@...nel.org>,
        Florian Fainelli <florian.fainelli@...adcom.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Phil Elwell <phil@...pberrypi.com>
Cc:     Mike Isely <isely@...ox.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] [i2c-bcm2835] Fully clean up hardware state machine
 after a timeout

[Forward to Dave and Phil]

Am 30.10.23 um 17:21 schrieb mike.isely@...altdigital.com:
> From: Mike Isely <mike.isely@...altdigital.com>
>
> When the driver detects a timeout, there's no guarantee that the ISR
> would have fired.  Thus after a timeout, it's the foreground that
> becomes responsible to reset the hardware state machine.  The change
> here just duplicates what is already implemented in the ISR.
>
> Signed-off-by: Mike Isely <isely@...ox.com>
> ---
>   drivers/i2c/busses/i2c-bcm2835.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
> index 8ce6d3f49551..96de875394e1 100644
> --- a/drivers/i2c/busses/i2c-bcm2835.c
> +++ b/drivers/i2c/busses/i2c-bcm2835.c
> @@ -345,42 +345,46 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data)
>   static int bcm2835_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
>   			    int num)
>   {
>   	struct bcm2835_i2c_dev *i2c_dev = i2c_get_adapdata(adap);
>   	unsigned long time_left;
>   	int i;
>
>   	for (i = 0; i < (num - 1); i++)
>   		if (msgs[i].flags & I2C_M_RD) {
>   			dev_warn_once(i2c_dev->dev,
>   				      "only one read message supported, has to be last\n");
>   			return -EOPNOTSUPP;
>   		}
>
>   	i2c_dev->curr_msg = msgs;
>   	i2c_dev->num_msgs = num;
>   	reinit_completion(&i2c_dev->completion);
>
>   	bcm2835_i2c_start_transfer(i2c_dev);
>
>   	time_left = wait_for_completion_timeout(&i2c_dev->completion,
>   						adap->timeout);
>
>   	bcm2835_i2c_finish_transfer(i2c_dev);
>
>   	if (!time_left) {
> +		/* Since we can't trust the ISR to have cleaned up, do the
> +		 * full cleanup here... */
>   		bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C,
>   				   BCM2835_I2C_C_CLEAR);
> +		bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_S, BCM2835_I2C_S_CLKT |
> +				   BCM2835_I2C_S_ERR | BCM2835_I2C_S_DONE);
>   		dev_err(i2c_dev->dev, "i2c transfer timed out\n");
>   		return -ETIMEDOUT;
>   	}
>
>   	if (!i2c_dev->msg_err)
>   		return num;
>
>   	dev_dbg(i2c_dev->dev, "i2c transfer failed: %x\n", i2c_dev->msg_err);
>
>   	if (i2c_dev->msg_err & BCM2835_I2C_S_ERR)
>   		return -EREMOTEIO;
>
>   	return -EIO;
>   }