From: Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>
To: Michael Lawnick <ml.lawnick-Mmb7MZpHnFY@public.gmane.org>
Cc: Ben Dooks <ben.dooks-4yDnlxn2s6sWdaTGBSpHTA@public.gmane.org>,
linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
SH-Linux <linux-sh-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: rcar-i2c: always reads a byte
Date: Mon, 5 May 2014 15:21:11 +0200 [thread overview]
Message-ID: <20140505132111.GA13467@katana> (raw)
In-Reply-To: <53201A83.7040605-Mmb7MZpHnFY@public.gmane.org>
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> >I have noticed the following behaviour with the i2c-rcar driver
> >with the following single i2c_msg structure:
> >
> > msg[0].addr = 0x12;
> > msg[0].flags = I2C_M_RD;
> > msg[0].len = 0;
> > msg[0].buf = data;
>
> isn't this illegal?
> This should lead to 50% chance of blocked bus: After sending
> read-bit the slave ACK's and puts first data bit onto SDL.
It is not illegal, SMBUS_QUICK is described in the SMBus specs and can
bee seen as a kind of 1-bit transfer. Yet, you should only issue it for
devices which require exactly this kind of transfer. Which is true for
most I2C transaction types.
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WARNING: multiple messages have this Message-ID (diff)
From: Wolfram Sang <wsa@the-dreams.de>
To: Michael Lawnick <ml.lawnick-Mmb7MZpHnFY@public.gmane.org>
Cc: Ben Dooks <ben.dooks-4yDnlxn2s6sWdaTGBSpHTA@public.gmane.org>,
linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
SH-Linux <linux-sh-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: rcar-i2c: always reads a byte
Date: Mon, 05 May 2014 13:21:11 +0000 [thread overview]
Message-ID: <20140505132111.GA13467@katana> (raw)
In-Reply-To: <53201A83.7040605-Mmb7MZpHnFY@public.gmane.org>
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> >I have noticed the following behaviour with the i2c-rcar driver
> >with the following single i2c_msg structure:
> >
> > msg[0].addr = 0x12;
> > msg[0].flags = I2C_M_RD;
> > msg[0].len = 0;
> > msg[0].buf = data;
>
> isn't this illegal?
> This should lead to 50% chance of blocked bus: After sending
> read-bit the slave ACK's and puts first data bit onto SDL.
It is not illegal, SMBUS_QUICK is described in the SMBus specs and can
bee seen as a kind of 1-bit transfer. Yet, you should only issue it for
devices which require exactly this kind of transfer. Which is true for
most I2C transaction types.
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next prev parent reply other threads:[~2014-05-05 13:21 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-11 16:15 rcar-i2c: always reads a byte Ben Dooks
2014-03-11 16:40 ` Wolfram Sang
2014-03-11 16:40 ` Wolfram Sang
2014-03-11 16:41 ` Ben Dooks
2014-03-11 16:47 ` Wolfram Sang
2014-03-11 16:47 ` Wolfram Sang
2014-03-11 17:10 ` Ben Dooks
2014-05-05 15:51 ` Wolfram Sang
2014-05-05 15:51 ` Wolfram Sang
2014-03-11 17:24 ` Wolfram Sang
2014-03-11 17:24 ` Wolfram Sang
2014-03-11 17:31 ` Ben Dooks
2014-03-11 17:46 ` Wolfram Sang
2014-03-11 17:46 ` Wolfram Sang
[not found] ` <531F3686.7050808-4yDnlxn2s6sWdaTGBSpHTA@public.gmane.org>
2014-03-12 8:27 ` Michael Lawnick
2014-03-12 8:27 ` Michael Lawnick
2014-03-12 8:39 ` Paul Carpenter
2014-03-12 9:00 ` Michael Lawnick
2014-03-12 9:00 ` Michael Lawnick
[not found] ` <53201A83.7040605-Mmb7MZpHnFY@public.gmane.org>
2014-05-05 13:21 ` Wolfram Sang [this message]
2014-05-05 13:21 ` Wolfram Sang
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