linux-kernel - Re: [PATCH v2 2/2] i2c: qup: support SMBus block read

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Message-ID: <4ca84ab1-f558-25b1-2fa5-dbcf9e8cc2e7@codeaurora.org>
Date:	Mon, 23 May 2016 11:45:51 -0600
From:	"Christ, Austin" <austinwc@...eaurora.org>
To:	Sricharan <sricharan@...eaurora.org>,
	'Naveen Kaje' <nkaje@...eaurora.org>, wsa@...-dreams.de,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	linux-arm-msm@...r.kernel.org, rruigrok@...eaurora.org,
	timur@...eaurora.org, cov@...eaurora.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/2] i2c: qup: support SMBus block read



On 5/20/2016 2:31 AM, Sricharan wrote:
> Hi,
>
> <snip..>
>>>> @@ -1128,6 +1173,22 @@ static int qup_i2c_read_one_v2(struct
>>>> qup_i2c_dev *qup, struct i2c_msg *msg)
>>>>    			goto err;
>>>>
>>>>    		qup->blk.pos++;
>>>> +
>>>> +		/* Handle SMBus block read length */
>>>> +		if (qup_i2c_check_msg_len(msg) && (msg->len == 1)) {
>>>> +			if (msg->buf[0] > I2C_SMBUS_BLOCK_MAX) {
>>>> +				ret = -EPROTO;
>>>> +				goto err;
>>>> +			}
>>>> +			msg->len += msg->buf[0];
>>>> +			qup->pos = 0;
>>>> +			qup_i2c_set_read_mode_v2(qup, msg->len);
>>>> +			qup_i2c_issue_xfer_v2(qup, msg);
>>>> +			ret = qup_i2c_wait_for_complete(qup, msg);
>>>> +			if (ret)
>>>> +				goto err;
>>> 		Is the issue_xfer_v2 needed inside this here ?
>> No, qup_i2c_issue_xfer_v2 is needed so that we read rest of the data
>> that is indicated by the length we read earlier.
> So qup_i2c_issue_xfer_v2 writes the tags and there is one already in the loop above this
>   check. So if you just do qup_i2c_set_read_mode_v2 and qup_i2c_set_blk_data inside this
>   check, will not be enough ?
>
> Regards,
>   Sricharan
>
In testing, removing the call to qup_i2c_issue_xfer_v2() within the 
conditional statement for SMBus length causes failures. That transfer 
request is needed to read that block of data.

Thanks,
Austin