linux-kernel - Re: PCF857x and 16-bit GPIO expanders

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Message-ID: <523AF014.5040806@newflow.co.uk>
Date:	Thu, 19 Sep 2013 13:37:40 +0100
From:	Mark Jackson <mpfj-list@...flow.co.uk>
To:	George Cherian <george.cherian@...com>
CC:	Nishanth Menon <nm@...com>, balbi@...com,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>
Subject: Re: PCF857x and 16-bit GPIO expanders

On 19/09/13 13:20, George Cherian wrote:
> On 9/19/2013 5:37 PM, Nishanth Menon wrote:
>> On 09/19/2013 03:13 AM, George Cherian wrote:
>>> On 9/18/2013 11:06 PM, Felipe Balbi wrote:
>>>> Hi,
>>>>
>>>> On Wed, Sep 18, 2013 at 07:18:04PM +0200, Laurent Pinchart wrote:
>>>>> On Wednesday 18 September 2013 13:16:27 Linus Walleij wrote:
>>>>>> On Tue, Sep 17, 2013 at 9:07 PM, Felipe Balbi <balbi@...com> wrote:
>>>>>>> has anyone ever successfully using gpio-pcf857x.c driver with 16-bit
>>>>>>> gpio expanders ? We're having some issues here where toggling the last
>>>>>>> gpio pin (gpio 15) on a PCF8575 device causes platform to hang and I
>>>>>>> can't come up with any explanation of why would it hang...
>>>>>> Bouncing the question to George, Laurent and Kuninori...
>>>>> I've got a board with a PCF8575 chip, but it uses I/Os 8 to 14 only as far as
>>>>> I know.
>>>>>
>>>>> I can try toggling I/O 15, but that will need to wait until next week as I'm
>>>>> currently travelling without access to the hardware.
>>>> alright, that'd help me a lot :-) Just want to make sure if we're having
>>>> a board issue, or PCF8575 is a bit screwy ;-)
>>> Is it on dra7x-evm if so which pcf device (i2c address)?
>>> The pins i were interested were only 1 and 2 I never tried pin 15.
>>>
>>> Just tried toggling through sysfs and it works for me.
>> When I look at the data sheet for PCF8575[1] Page 7, Figure 4 Write
>> mode (output)
>> I see the data writes are of the order:
>> I2c 1's byte: address
>> I2c 2'nd byte:P[7-0]
>> I2c 3rd byte:P[17-10]
> 
> I read it as an octal numbering.

Kind of ... looking at the pinout, you have pins:-

P00...P07
P10...P17

So that's Port 0, bits 0..7, and Port 1, bits 0..7.

Mark J.
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