| Message ID | CAHNNwZAucoc00gJrUsPRMpFc9U2r+os6NJfc1axsGh0m6ES=xQ@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | gpiolib sysfs access when CONFIG_GPIO_CDEV is not set | expand |
On Wed, Nov 04, 2020 at 06:26:54PM +0100, Nicolas Schichan wrote: > Hello, > > Following an update to the 5.10-rc1 kernel, I found out that trying to > export a GPIO using /sys/class/gpio/export fails with the kernel > reporting a message in the kernel logs: > > # echo 41 >/sys/class/gpio/export > [ 46.761394] kobject_add_internal failed for gpio (error: -2 parent: > gpiochip2) > sh: write error: No such file or directory > # > > I have tracked it to the fact that I have CONFIG_GPIO_CDEV is disabled in > my kernel config: Enabling CONFIG_GPIO_CDEV made export work again. > Hi Nicolas, Thanks for the report and investigation. Just checking - the CONFIG_GPIO_CDEV defaults to enabled, so you had explicitly disabled it? > Enabling CONFIG_GPIO_CDEV and commenting all the code in > gpiolib_cdev_register() except the final "return 0;" made the issue > appear again, leading me to think that the issue is related to > something that is done cdev_device_add() must be done to fix the > issue. > > Looking at the code of cdev_device_add() I was able to determine that > the device_add() call made there is required to get the gpiolib sysfs > export to work again. > So the sysfs init, and the remainder of gpiochip_setup_dev(), relies on the cdev init to perform the device_add() - I missed that :(. > In the end I have done this (which I won't even pretend is the proper > way to fix this), and sysfs attributes are finally working without > CONFIG_GPIO_CDEV: > I'd prefer this dependency was made more explicit, so I'd be inclined to relocate the ifdef CONFIG_GPIO_CDEV block from gpiolib-cdev.h into gpiolib.c by adding helper functions that call either the gpiolib_cdev_register/unregister or the device_add/del dependent on CONFIG_GPIO_CDEV. I'll try to get a patch out shortly. Thanks, Kent. > diff --git a/drivers/gpio/gpiolib-cdev.h b/drivers/gpio/gpiolib-cdev.h > index cb41dd757338..dd72bd0e4af4 100644 > --- a/drivers/gpio/gpiolib-cdev.h > +++ b/drivers/gpio/gpiolib-cdev.h > @@ -16,7 +16,7 @@ void gpiolib_cdev_unregister(struct gpio_device *gdev); > > static inline int gpiolib_cdev_register(struct gpio_device *gdev, dev_t devt) > { > - return 0; > + return device_add(&gdev->dev); > } > > static inline void gpiolib_cdev_unregister(struct gpio_device *gdev) > > If this is the preferred solution I can send a proper patch. > > Best Regards, > > -- > Nicolas Schichan
On Thu, Nov 5, 2020 at 9:39 AM Kent Gibson <warthog618@gmail.com> wrote: [...] > Hi Nicolas, > > Thanks for the report and investigation. > > Just checking - the CONFIG_GPIO_CDEV defaults to enabled, so you had > explicitly disabled it? Hello Kent, Yes, we have no users of the character device gpio interface on our platform, so I have disabled it explicitly when updating the defconfig to the 5.10-rc1 kernel. Regards, -- Nicolas Schichan
On Thu, Nov 05, 2020 at 01:07:43PM +0100, Nicolas Schichan wrote: > On Thu, Nov 5, 2020 at 9:39 AM Kent Gibson <warthog618@gmail.com> wrote: > [...] > > Hi Nicolas, > > > > Thanks for the report and investigation. > > > > Just checking - the CONFIG_GPIO_CDEV defaults to enabled, so you had > > explicitly disabled it? > > Hello Kent, > > Yes, we have no users of the character device gpio interface on our > platform, so I have disabled it explicitly when updating the defconfig > to the 5.10-rc1 kernel. > Thanks for confirming that - I was concerned that it had somehow been disabled unintentionally - which would be a bug in itself. Cheers, Kent.
On Wed, Nov 4, 2020 at 6:27 PM Nicolas Schichan <nschichan@freebox.fr> wrote: > I have tracked it to the fact that I have CONFIG_GPIO_CDEV is disabled in > my kernel config: Enabling CONFIG_GPIO_CDEV made export work again. We have deliberately made it hard to remove the character device because we want to encourage people to use it. > Yes, we have no users of the character device gpio interface on our > platform, so I have disabled it explicitly when updating the defconfig > to the 5.10-rc1 kernel. Please consider getting users of the character device, since if they are using the sysfs they are using an explicitly obsoleted interface. Yours, Linus Walleij
diff --git a/drivers/gpio/gpiolib-cdev.h b/drivers/gpio/gpiolib-cdev.h index cb41dd757338..dd72bd0e4af4 100644 --- a/drivers/gpio/gpiolib-cdev.h +++ b/drivers/gpio/gpiolib-cdev.h @@ -16,7 +16,7 @@ void gpiolib_cdev_unregister(struct gpio_device *gdev); static inline int gpiolib_cdev_register(struct gpio_device *gdev, dev_t devt) { - return 0; + return device_add(&gdev->dev); } static inline void gpiolib_cdev_unregister(struct gpio_device *gdev)