linux-kernel - Re: [PATCH 4/4] i2c: xlp9xx: Check for Bus state after every transfer

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Message-ID: <a96c4bb2-fbc5-3e21-f6b5-4da75fac3c01@caviumnetworks.com>
Date:   Tue, 27 Feb 2018 10:30:31 +0530
From:   George Cherian <gcherian@...iumnetworks.com>
To:     Wolfram Sang <wsa@...-dreams.de>,
        George Cherian <george.cherian@...ium.com>
Cc:     linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH 4/4] i2c: xlp9xx: Check for Bus state after every transfer

Hi Wolfram,

Thanks for the review.

On 02/27/2018 01:52 AM, Wolfram Sang wrote:
> 
> On Thu, Jan 18, 2018 at 05:39:24AM +0000, George Cherian wrote:
>> I2C bus enters the STOP condition after the DATA_DONE interrupt is raised.
>> Essentially the driver should be checking the bus state before sending
>> the next transaction.
> 
> Yes.
> 
>> In case the next transaction is initiated while the
>> bus is busy, the prior transactions stop condition is not achieved.
> 
> I didn't fully get why you can't check the BUSY bit and wait a little
> just before you push out the next message?
Yes, I am checking for the BUSY bit and looping.
Here for reference

+	while (last_msg && busy_timeout) {
+		status = xlp9xx_read_i2c_reg(priv, XLP9XX_I2C_STATUS);
+		if ((status & XLP9XX_I2C_STATUS_BUSY) == 0)
+			break;
+
+		busy_timeout--;
+		udelay(1);
+	}
+
+	if (!busy_timeout) {
+		dev_dbg(priv->dev, "i2c bus busy for too long after transfer\n");
+		return -EIO;
+	}

Did you mean to eliminate the udelay and use msleep?
In any case I will re-post another version of the patch, since
I have found some more issues and need to be fixed.

> 
>> Add the check to make sure the bus is not busy before next transaction.
>>

Regards,
-George