linux-kernel - Re: [PATCH 3/8 v3] i2c: i801: check INTR after every transaction

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Message-ID: <20120702171620.5628d044@endymion.delvare>
Date:	Mon, 2 Jul 2012 17:16:20 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	Daniel Kurtz <djkurtz@...omium.org>
Cc:	Ben Dooks <ben-linux@...ff.org>,
	Wolfram Sang <w.sang@...gutronix.de>,
	Seth Heasley <seth.heasley@...el.com>,
	Olof Johansson <olof@...om.net>,
	Benson Leung <bleung@...omium.org>, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8 v3] i2c: i801: check INTR after every transaction

On Mon, 2 Jul 2012 12:08:14 +0200, Jean Delvare wrote:
> On Mon, 2 Jul 2012 09:19:24 +0800, Daniel Kurtz wrote:
> > My understanding is that the INTR wait is really waiting for the
> > entire transaction to complete (ie., including i2c STOP condition),
> > not just the byte transfer phase.
> 
> This is my understanding as well, but I'm fairly certain that this is
> the case of the BUSY flag as well. I think BUSY gets cleared at the
> same time INTR (or any of the error status bits) gets set. Which is why
> I think checking BUSY is redundant. As a matter of fact, we ignore BUSY
> completely in i801_block_transaction_byte_by_byte(), so I see no reason
> why we couldn't do the same in i2c_transaction().

To be complete, I made some testing and error bits can be set before
BUSY is cleared. I spotted several transitions 0x41 -> 0x45 -> 0x44
when accessing non-existent devices. On success, I never witnessed INTR
and BUSY being set at the same time, transition is always 0x41 -> 0x42.

-- 
Jean Delvare
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