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Message-ID: <511481A2.7010100@linux.intel.com>
Date: Thu, 07 Feb 2013 20:40:02 -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.
>
> Configure in debugfs and check the file "gpio" in debugfs
> to figure out the client.
>
> Yours,
> Linus Walleij
>
I found gpio_export() as you suggested above and instrumented it. What I
found was that it was not getting called at all. As I understand it,
calling gpiochip_export() should make the gpiochip# appear in
/sys/class/gpio and then I should be able to configure which lines are
exported via the /sys/class/gpio/export file.
I haven't yet found how gpio-pch differs from gpio-sch that causes the
gpio-pch chip to appear in sysfs and the gpio-sch one not to. I did
patch gpio-sch with a request and export loop:
$ git diff drivers/gpio/gpio-sch.c
diff --git a/drivers/gpio/gpio-sch.c b/drivers/gpio/gpio-sch.c
index 8cadf4d..79783c1 100644
--- a/drivers/gpio/gpio-sch.c
+++ b/drivers/gpio/gpio-sch.c
@@ -188,7 +188,7 @@ static struct gpio_chip sch_gpio_resume = {
static int __devinit sch_gpio_probe(struct platform_device *pdev)
{
struct resource *res;
- int err, id;
+ int err, id, gpio;
id = pdev->id;
if (!id)
@@ -243,10 +243,24 @@ static int __devinit sch_gpio_probe(struct
platform_device *p
if (err < 0)
goto err_sch_gpio_core;
+ /* DEBUG: export all the core GPIOS */
+ for (gpio = sch_gpio_core.base;
+ gpio < sch_gpio_core.base + sch_gpio_core.ngpio; gpio++) {
+ gpio_request(gpio, "gpio-sch");
+ gpio_export(gpio, true);
+ }
+
err = gpiochip_add(&sch_gpio_resume);
if (err < 0)
goto err_sch_gpio_resume;
+ /* DEBUG: export all the resume GPIOS */
+ for (gpio = sch_gpio_resume.base;
+ gpio < sch_gpio_resume.base + sch_gpio_resume.ngpio; gpio++) {
+ gpio_request(gpio, "gpio-sch");
+ gpio_export(gpio, true);
+ }
+
return 0;
err_sch_gpio_resume:
With this both the gpiochip# and gpio# entries appear in sysfs. However,
unlike those for the gpio-pch lines, these report an error in the sysfs
interface:
/sys/class/gpio# ls *
ls: gpio0: No such file or directory
ls: gpio1: No such file or directory
ls: gpio10: No such file or directory
ls: gpio11: No such file or directory
ls: gpio12: No such file or directory
ls: gpio13: No such file or directory
ls: gpio2: No such file or directory
ls: gpio3: No such file or directory
ls: gpio4: No such file or directory
ls: gpio5: No such file or directory
ls: gpio6: No such file or directory
ls: gpio7: No such file or directory
ls: gpio8: No such file or directory
ls: gpio9: No such file or directory
ls: gpiochip0: No such file or directory
ls: gpiochip5: No such file or directory
export unexport
gpiochip244:
base label ngpio power subsystem uevent
Clearly I'm still missing something. I've read through gpio.txt a couple
times and each time piece a bit more together. I'll do that again, but I
still suspect I'm missing something fundamental here. In particular, I
still don't understand how the gpio-pch and gpio-sch drivers are create
such different results.
Ultimately what I'm looking to do is configure a new board such that 8
of the gpio-sch lines are configured as buttons and LEDs which are
physically attached to the board (4 of each). I was hoping to use this
interface to understand the ins and outs (haha) of the GPIO subsystem.
Ultimately I believe I need either a "platform-device" or possibly an
ACPI DSDT from the firmware to properly describe the GPIO lines and
their direction. Ultimately, these should be driven by the gpio-keys and
gpio-led drivers - at least that's my current understanding.
Any help clarifying some of this would be greatly appreciated.
Thanks for the time!
--
Darren Hart
Intel Open Source Technology Center
Yocto Project - Technical Lead - Linux Kernel
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