linux-kernel - Re: [RFC 01/11] i2c: add quirk structure to describe adapter flaws

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Message-ID: <1421396295.11671.50.camel@mtksdaap41>
Date:	Fri, 16 Jan 2015 16:18:15 +0800
From:	Yingjoe Chen <yingjoe.chen@...iatek.com>
To:	Wolfram Sang <wsa@...-dreams.de>
CC:	<linux-i2c@...r.kernel.org>, <linux-mips@...ux-mips.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	<linux-kernel@...r.kernel.org>,
	Ludovic Desroches <ludovic.desroches@...el.com>,
	<linuxppc-dev@...ts.ozlabs.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	Eddie Huang <eddie.huang@...iatek.com>,
	Xudong Chen <xudong.chen@...iatek.com>,
	Liguo Zhang <Liguo.Zhang@...iatek.com>
Subject: Re: [RFC 01/11] i2c: add quirk structure to describe adapter flaws

On Fri, 2015-01-09 at 18:21 +0100, Wolfram Sang wrote:
> The number of I2C adapters which are not fully I2C compatible is rising,
> sadly. Drivers usually do handle the flaws, still the user receives only
> some errno for a transfer which normally can be expected to work. This
> patch introduces a formal description of flaws. One advantage is that
> the core can check before the actual transfer if the messages could be
> transferred at all. This is done in the next patch. Another advantage is
> that we can pass this information to the user so the restrictions are
> exactly known and further actions can be based on that. This will be
> done later after some stabilization period for this description.

Hi Wolfram,

This can describe the behavior of our current upstream driver[1], which
only support combine write-then-read.

After checking with Xudong & HW guys, it seems our HW can do more. 
On MT8135, it can support at most 2 messages, no matter read or write,
with the limitation that the length of the second message must <=
31bytes.

So this RFC is enough for our driver, but it would be better if we could
also support other case.

Joe.C

[1]:
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/305468.html



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