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

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Date:   Tue, 27 Feb 2018 10:41:06 +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,


On 02/27/2018 10:30 AM, George Cherian wrote:
> 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.

Since you raised concern on the patch I thought of reworking this patch.
But I can see that this patch is already applied for i2c/for-next.
Kindly let me know whether I should be sending follow-up patches on top
of i2c/for-next ?
> 
>>
>>> Add the check to make sure the bus is not busy before next transaction.
>>>
> 
> Regards,
> -George

Regards,
-George