Messages in this thread Patch in this message | | | Date | Thu, 07 Feb 2013 20:40:02 -0800 | From | Darren Hart <> | 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@linux.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
| |