linux-kernel - RE: [PATCH] i2c-cadence: Do not let signals interrupt I2C transfers

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Message-ID: <b6f0755f-cfc9-4962-851f-5eeac767e93e@AM1EHSMHS008.ehs.local>
Date:	Tue, 11 Mar 2014 04:49:16 +0000
From:	Suneel Garapati <suneel.garapati@...inx.com>
To:	Soren Brinkmann <sorenb@...inx.com>,
	Mike Looijmans <mike.looijmans@...ic.nl>,
	Michal Simek <michals@...inx.com>
CC:	git <git@...inx.com>, "wsa@...-dreams.de" <wsa@...-dreams.de>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] i2c-cadence: Do not let signals interrupt I2C transfers

Hi Mike/Soren,

> -----Original Message-----
> From: Sören Brinkmann [mailto:soren.brinkmann@...inx.com]
> Sent: Tuesday, March 11, 2014 03:30
> To: Mike Looijmans; Michal Simek
> Cc: git; wsa@...-dreams.de; linux-i2c@...r.kernel.org; linux-
> kernel@...r.kernel.org
> Subject: Re: [PATCH] i2c-cadence: Do not let signals interrupt I2C transfers
>
> Hi Mike,
>
> The cadence driver is not in mainline yet. I think for our vendor tree we can
> pretty much take it this way.
> Regarding getting this into mainline, I'll send another iteration of the change
> set and include these changes.
>
> On Mon, 2014-03-10 at 12:12PM +0100, Mike Looijmans wrote:
> > Pressing CTRL-C while communicating with an I2C device leads to
> > erratic behaviour. The cause is that the controller will interrupt the
> > I2C transfer in progress, and leave the client device in an undefined
> > state. Many drivers do not handle error return codes on I2C transfers.
> > The calling driver has no way of telling how much of the transfer has
> > actually completed, so it cannot reliably determine the device's state.
> >
> > The best solution here is to not handle signals in the I2C bus driver
> > at all, but always complete a transaction before returning control.
> >
> > See for a related patch and discussion on this topic:
> > http://lkml.org/lkml/2014/1/9/246
>
> Can we get your Signed-off-by, please?
>
> > ---
> >  drivers/i2c/busses/i2c-cadence.c |   12 ++++--------
> >  1 file changed, 4 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-cadence.c
> > b/drivers/i2c/busses/i2c-cadence.c
> > index 86713d6..32ce2ee 100644
> > --- a/drivers/i2c/busses/i2c-cadence.c
> > +++ b/drivers/i2c/busses/i2c-cadence.c
> > @@ -452,16 +452,12 @@ static int cdns_i2c_process_msg(struct cdns_i2c
> *id, struct i2c_msg *msg,
> >                     cdns_i2c_msend(id);
> >
> >             /* Wait for the signal of completion */
> > -           ret = wait_for_completion_interruptible_timeout(
> > -                                                   &id->xfer_done, HZ);
> > -           if (ret < 1) {
> > +           ret = wait_for_completion_timeout(&id->xfer_done, HZ);
> > +           if (ret == 0) {
>
> To match the style used throughout the file this should just be
>       if (!ret) {
Instead of discarding Ctrl+C, Can we wait until the current msg transfer completes
[to avoid client undefined state or re-init the host to a known state]

I see da-vinci driver handling in a similar way.

Regards,
Suneel

>
>
> Acked-by: Soren Brinkmann <soren.brinkmann@...inx.com>
>
>       Thanks,
>       Sören



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