linux-kernel - Re: [PATCH v4 2/2] i2c: cadence: Check for errata condition involving master receive

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Date:	Wed, 10 Dec 2014 09:45:54 -0800
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Harini Katakam <harini.katakam@...inx.com>
CC:	<wsa@...-dreams.de>, <mark.rutland@....com>,
	<michal.simek@...inx.com>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<harinikatakamlinux@...il.com>, <harinik@...inx.com>,
	Vishnu Motghare <vishnum@...inx.com>
Subject: Re: [PATCH v4 2/2] i2c: cadence: Check for errata condition
 involving master receive

On Wed, 2014-12-10 at 05:14PM +0530, Harini Katakam wrote:
> Cadence I2C controller has the following bugs:
> - completion indication is not given to the driver at the end of
> a read/receive transfer with HOLD bit set.
> - Invalid read transaction are generated on the bus when HW timeout
> condition occurs with HOLD bit set.
> 
> As a result of the above, if a set of messages to be transferred with
> repeated start includes any transfer following a read transfer,
> completion is never indicated and timeout occurs.
> Hence a check is implemented to return -EOPNOTSUPP for such sequences.
> 
> Signed-off-by: Harini Katakam <harinik@...inx.com>
> Signed-off-by: Vishnu Motghare <vishnum@...inx.com>
> ---
> 
> v4:
> Use single dev_warn and make message grep-able.
> 
> v3:
> Add warning in case of unsupported transfer.
> 
> v2:
> Dont defeteature repeated start. Just check for unsupported conditions in the
> driver and return error.
> 
> ---
>  drivers/i2c/busses/i2c-cadence.c |   14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
> index 5f5d4fa..f9269a6 100644
> --- a/drivers/i2c/busses/i2c-cadence.c
> +++ b/drivers/i2c/busses/i2c-cadence.c
> @@ -541,6 +541,20 @@ static int cdns_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
>  	 * processed with a repeated start.
>  	 */
>  	if (num > 1) {
> +		/*
> +		 * This controller does not give completion interrupt after a
> +		 * master receive transfer if HOLD bit is set (repeated start),
> +		 * resulting in SW timeout. Hence, if a receive transfer is
> +		 * followed by any other transfer, an error is returned
> +		 * indicating that this sequence is not supported.
> +		 */
> +		for (count = 0; count < num-1; count++) {
> +			if (msgs[count].flags & I2C_M_RD)
> +				dev_warn(adap->dev.parent, "No support for "
> +					 "repeated start when receive is "
> +					 "followed by a transfer\n");

Still not grepable. There must be no line breaks in the string!

	Sören
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