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

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Date:	Thu, 11 Dec 2014 09:28:59 -0800
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Harini Katakam <harinikatakamlinux@...il.com>
CC:	Harini Katakam <harini.katakam@...inx.com>,
	"wsa@...-dreams.de" <wsa@...-dreams.de>,
	Mark Rutland <mark.rutland@....com>,
	Michal Simek <michal.simek@...inx.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Vishnu Motghare <vishnum@...inx.com>
Subject: Re: [PATCH v4 2/2] i2c: cadence: Check for errata condition
 involving master receive

On Thu, 2014-12-11 at 12:46PM +0530, Harini Katakam wrote:
> Hi Soren,
> 
> On Wed, Dec 10, 2014 at 11:15 PM, Sören Brinkmann
> <soren.brinkmann@...inx.com> wrote:
> > 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!
> 
> This message will be printed in one single line.
> Do you want this string to be grepable in the driver? Why is that necessary?

It's about grepping the sources.
I pointed you to the paragraph in the Codingstyle rules, please read
it.

	Sören
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