linux-kernel - Re: [RESEND2 PATCH v4 2/2] i2c: sunxi: add P2WI (Push/Pull 2 Wire Interface) controller support

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Message-ID: <5396C848.8020701@pcserviceselectronics.co.uk>
Date:	Tue, 10 Jun 2014 09:56:40 +0100
From:	Paul Carpenter <paul@...erviceselectronics.co.uk>
To:	Wolfram Sang <wsa@...-dreams.de>
CC:	Boris BREZILLON <boris.brezillon@...e-electrons.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Hans de Goede <hdegoede@...hat.com>,
	Shuge <shuge@...winnertech.com>, kevin@...winnertech.com,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-i2c@...r.kernel.org
Subject: Re: [RESEND2 PATCH v4 2/2] i2c: sunxi: add P2WI (Push/Pull 2 Wire
 Interface) controller support

Wolfram Sang wrote:
> On Tue, Jun 03, 2014 at 10:49:52AM +0200, Boris BREZILLON wrote:
>> The P2WI looks like an SMBus controller which only supports byte data
>> transfers. But, it differs from standard SMBus protocol on several
>> aspects:
>> - it supports only one slave device, and thus drop the address field
>> - it adds a parity bit every 8bits of data
>> - only one read access is required to read a byte (instead of a read
>>   followed by a write access in standard SMBus protocol)

Minor quibble should be
"(instead of a write followed by a read access in standard SMBus
   protocol)"

That being similar to EEPROM and other types of devices write internal
address followed by read access from internal address.

>> - there's no Ack bit after each byte transfer
>>
>> This means this bus cannot be used to interface with standard SMBus
>> devices (the only known device to support this interface is the AXP221
>> PMIC).
> 
> Good description. Should be a comment at the top of the driver to spread
> the word.

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