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

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Date:	Thu, 19 Sep 2013 17:50:28 +0530
From:	George Cherian <george.cherian@...com>
To:	Nishanth Menon <nm@...com>
CC:	<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 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.
> Note: bits 8,9 are missing not supported.

In octal there is no 8 and 9
>
> Now [2] claims that it does support PCF8575, however when I look at
> line 143[3]
> 	unsigned	bit = 1 << offset;
> [snip]
> 	if (value)
> 		gpio->out |= bit;
> 	else
> 		gpio->out &= ~bit;
>
> There is no handling for the skip needed for bits 8 and 9.. Seems to
> me like a driver bug.

In which case there is no driver bug
> [1] http://www.ti.com/lit/ds/symlink/pcf8575.pdf
> [2]
> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpio-pcf857x.c
> [3]
> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpio-pcf857x.c#n143


-- 
-George

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