linux-kernel - Re: [PATCH] i2c: cadence: Handling Slave monitor mode

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Message-ID: <20150402202909.GA3501@katana>
Date:	Thu, 2 Apr 2015 22:29:09 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Harini Katakam <harinikatakamlinux@...il.com>
Cc:	Nava kishore Manne <nava.manne@...inx.com>,
	Michal Simek <michal.simek@...inx.com>,
	Sören Brinkmann <soren.brinkmann@...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>,
	anirudh@...inx.com, svemula@...inx.com,
	Nava kishore Manne <navam@...inx.com>
Subject: Re: [PATCH] i2c: cadence: Handling Slave monitor mode


> >> In slave monitor mode, the I2C interface is set up as a master and
> >> continues to attempt a transfer to a particular slave until the
> >> slave device responds with an ACK.
> >>
> >> Added this feature for zero length transfers enable the controller
> >> for slave monitor interrupt and get the status. Disable the slave
> >> monitor mode feature upon successful handling.
> >>
> >> Signed-off-by: Nava kishore Manne <navam@...inx.com>
> >> Acked-by: Harini Katakam <harinik@...inx.com>
> >
> > I am not sure this is going to work.
> >
> > How often is this access tried when there is no device? It should be
> > tried only once.
> 
> Once slave monitor is enabled in the host controller, it retries till there's an
> ACK or slave monitor is disabled. The SW wont be involved and need not

So, it is kind of flooding the bus until the timeout? That is not a
single zero byte message.

> be interrupted in this gap. The way this feature works in the controller though,
> I'm afraid there's no way to distinguish between no slave/ busy slave.
> The out is the software timeout in that case.
> Please suggest how to use this feature better.

I suggest to not use the feature and accept that this device cannot do
zero byte length messages.

Thanks,

   Wolfram


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