linux-kernel - Re: gpio-sch GPIO

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Date:	Thu, 07 Feb 2013 07:17:41 -0800
From:	Darren Hart <dvhart@...ux.intel.com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	"lkml," <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Denis Turischev <denis@...pulab.co.il>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: gpio-sch GPIO_SYSFS access

On 02/07/2013 02:09 AM, Linus Walleij wrote:
> On Thu, Feb 7, 2013 at 1:58 AM, Darren Hart <dvhart@...ux.intel.com> wrote:
> 
>> Is it that some other driver has claimed these GPIO lines? If so, how do
>> I determine which one?
> 
> Yes I think that could be it, the driver would need to call
> gpio_export() for it to also be accessible in sysfs.

Do you mean gpiochip_export()?

Hrm, neither gpio-pch nor gpio-sch call gpiochip_export() directly. They
both call gpiochip_add() and that calls gpiochip_export() unconditionally.
As far as I could tell, both drivers call gpiochip_export().

I thought maybe the sch happened to early, maybe hitting the the
pre-driver-model-support note in gpiochip_export(), but it runs after
the pch chip for some reason, and that one is fine. I suppose I could be
failing on device_create or sysfs_create_group and just not seeing the
output. I'll try to get DYNAMIC_DEBUG and pr_debug in gpiolib.c working
(that always seems to be an unnecessarily arduous exercise).

> 
> Configure in debugfs and check the file "gpio" in debugfs
> to figure out the client.

That file contained only the gpiochip244 from the gpio-pch driver,
nothing from the sch.

Thanks!

-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Technical Lead - Linux Kernel
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