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Date: Sat, 30 Jan 2021 20:39:50 +0300
From: Dmitry Osipenko <digetx@...il.com>
To: Saravana Kannan <saravanak@...gle.com>,
Linus Walleij <linus.walleij@...aro.org>,
Bartosz Golaszewski <bgolaszewski@...libre.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Marc Zyngier <maz@...nel.org>,
Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
Kever Yang <kever.yang@...k-chips.com>,
kernel-team@...roid.com, linux-gpio@...r.kernel.org,
linux-kernel@...r.kernel.org,
"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v5] gpiolib: Bind gpio_device to a driver to enable
fw_devlink=on by default
22.01.2021 22:35, Saravana Kannan пишет:
> There are multiple instances of GPIO device tree nodes of the form:
>
> foo {
> compatible = "acme,foo";
> ...
>
> gpio0: gpio0@...xxxxx {
> compatible = "acme,bar";
> ...
> gpio-controller;
> };
>
> gpio1: gpio1@...xxxxx {
> compatible = "acme,bar";
> ...
> gpio-controller;
> };
>
> ...
> }
>
> bazz {
> my-gpios = <&gpio0 ...>;
> }
>
> Case 1: The driver for "foo" populates struct device for these gpio*
> nodes and then probes them using a driver that binds with "acme,bar".
> This driver for "acme,bar" then registers the gpio* nodes with gpiolib.
> This lines up with how DT nodes with the "compatible" property are
> typically converted to struct devices and then registered with driver
> core to probe them. This also allows the gpio* devices to hook into all
> the driver core capabilities like runtime PM, probe deferral,
> suspend/resume ordering, device links, etc.
>
> Case 2: The driver for "foo" doesn't populate struct devices for these
> gpio* nodes before registering them with gpiolib. Instead it just loops
> through its child nodes and directly registers the gpio* nodes with
> gpiolib.
>
> Drivers that follow case 2 cause problems with fw_devlink=on. This is
> because fw_devlink will prevent bazz from probing until there's a struct
> device that has gpio0 as its fwnode (because bazz lists gpio0 as a GPIO
> supplier). Once the struct device is available, fw_devlink will create a
> device link with gpio0 device as the supplier and bazz device as the
> consumer. After this point, since the gpio0 device will never bind to a
> driver, the device link will prevent bazz device from ever probing.
>
> Finding and refactoring all the instances of drivers that follow case 2
> will cause a lot of code churn and it is not something that can be done
> in one shot. In some instances it might not even be possible to refactor
> them cleanly. Examples of such instances are [1] [2].
>
> This patch works around this problem and avoids all the code churn by
> simply setting the fwnode of the gpio_device and creating a stub driver
> to bind to the gpio_device. This allows all the consumers to continue
> probing when the driver follows case 2.
>
> [1] - https://lore.kernel.org/lkml/20201014191235.7f71fcb4@xhacker.debian/
> [2] - https://lore.kernel.org/lkml/e28e1f38d87c12a3c714a6573beba6e1@kernel.org/
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Jisheng Zhang <Jisheng.Zhang@...aptics.com>
> Cc: Kever Yang <kever.yang@...k-chips.com>
> Fixes: e590474768f1 ("driver core: Set fw_devlink=on by default")
> Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> ---
> v1 -> v2:
> - Fixed up compilation errors that were introduced accidentally
> - Fixed a missing put_device()
>
> v2 -> v3:
> - Changed chip_warn() to pr_warn()
> - Changed some variable names
>
> v3 -> v4:
> - Dropped the warning since it's not always valid
> - This simplifies the code a lot
> - Added comments and fixed up commit text
>
> v4 -> v5:
> - Fixed the code to not mess up non-DT cases.
> - Moved code into gpiolib-of.c
>
> drivers/gpio/gpiolib-of.c | 11 +++++++++++
> drivers/gpio/gpiolib-of.h | 5 +++++
> drivers/gpio/gpiolib.c | 38 +++++++++++++++++++++++++++++++-------
> 3 files changed, 47 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
> index b4a71119a4b0..baf0153b7bca 100644
> --- a/drivers/gpio/gpiolib-of.c
> +++ b/drivers/gpio/gpiolib-of.c
> @@ -1039,3 +1039,14 @@ void of_gpiochip_remove(struct gpio_chip *chip)
> {
> of_node_put(chip->of_node);
> }
> +
> +void of_gpio_dev_init(struct gpio_chip *gc, struct gpio_device *gdev)
> +{
> + /* If the gpiochip has an assigned OF node this takes precedence */
> + if (gc->of_node)
> + gdev->dev.of_node = gc->of_node;
> + else
> + gc->of_node = gdev->dev.of_node;
> + if (gdev->dev.of_node)
> + gdev->dev.fwnode = of_fwnode_handle(gdev->dev.of_node);
> +}
> diff --git a/drivers/gpio/gpiolib-of.h b/drivers/gpio/gpiolib-of.h
> index ed26664f1537..8af2bc899aab 100644
> --- a/drivers/gpio/gpiolib-of.h
> +++ b/drivers/gpio/gpiolib-of.h
> @@ -15,6 +15,7 @@ int of_gpiochip_add(struct gpio_chip *gc);
> void of_gpiochip_remove(struct gpio_chip *gc);
> int of_gpio_get_count(struct device *dev, const char *con_id);
> bool of_gpio_need_valid_mask(const struct gpio_chip *gc);
> +void of_gpio_dev_init(struct gpio_chip *gc, struct gpio_device *gdev);
> #else
> static inline struct gpio_desc *of_find_gpio(struct device *dev,
> const char *con_id,
> @@ -33,6 +34,10 @@ static inline bool of_gpio_need_valid_mask(const struct gpio_chip *gc)
> {
> return false;
> }
> +static inline void of_gpio_dev_init(struct gpio_chip *gc,
> + struct gpio_device *gdev)
> +{
> +}
> #endif /* CONFIG_OF_GPIO */
>
> extern struct notifier_block gpio_of_notifier;
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index b02cc2abd3b6..70fb15ae5d36 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -590,13 +590,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
> gdev->dev.of_node = gc->parent->of_node;
> }
>
> -#ifdef CONFIG_OF_GPIO
> - /* If the gpiochip has an assigned OF node this takes precedence */
> - if (gc->of_node)
> - gdev->dev.of_node = gc->of_node;
> - else
> - gc->of_node = gdev->dev.of_node;
> -#endif
> + of_gpio_dev_init(gc, gdev);
>
> gdev->id = ida_alloc(&gpio_ida, GFP_KERNEL);
> if (gdev->id < 0) {
> @@ -4202,6 +4196,29 @@ void gpiod_put_array(struct gpio_descs *descs)
> }
> EXPORT_SYMBOL_GPL(gpiod_put_array);
>
> +static int gpio_stub_drv_probe(struct device *dev)
> +{
> + /*
> + * The DT node of some GPIO chips have a "compatible" property, but
> + * never have a struct device added and probed by a driver to register
> + * the GPIO chip with gpiolib. In such cases, fw_devlink=on will cause
> + * the consumers of the GPIO chip to get probe deferred forever because
> + * they will be waiting for a device associated with the GPIO chip
> + * firmware node to get added and bound to a driver.
> + *
> + * To allow these consumers to probe, we associate the struct
> + * gpio_device of the GPIO chip with the firmware node and then simply
> + * bind it to this stub driver.
> + */
> + return 0;
> +}
> +
> +static struct device_driver gpio_stub_drv = {
> + .name = "gpio_stub_drv",
> + .bus = &gpio_bus_type,
> + .probe = gpio_stub_drv_probe,
> +};
> +
> static int __init gpiolib_dev_init(void)
> {
> int ret;
> @@ -4213,9 +4230,16 @@ static int __init gpiolib_dev_init(void)
> return ret;
> }
>
> + if (driver_register(&gpio_stub_drv) < 0) {
> + pr_err("gpiolib: could not register GPIO stub driver\n");
> + bus_unregister(&gpio_bus_type);
> + return ret;
> + }
> +
> ret = alloc_chrdev_region(&gpio_devt, 0, GPIO_DEV_MAX, GPIOCHIP_NAME);
> if (ret < 0) {
> pr_err("gpiolib: failed to allocate char dev region\n");
> + driver_unregister(&gpio_stub_drv);
> bus_unregister(&gpio_bus_type);
> return ret;
> }
>
Hi,
This patch causes these new errors on NVIDIA Tegra30 Nexus 7 using recent linux-next:
gpio-1022 (cpu-pwr-req-hog): hogged as input
max77620-pinctrl max77620-pinctrl: pin gpio4 already requested by max77620-pinctrl; cannot claim for gpiochip1
max77620-pinctrl max77620-pinctrl: pin-4 (gpiochip1) status -22
max77620-pinctrl max77620-pinctrl: could not request pin 4 (gpio4) from group gpio4 on device max77620-pinctrl
gpio_stub_drv gpiochip1: Error applying setting, reverse things back
gpio_stub_drv: probe of gpiochip1 failed with error -22
Please fix, thanks in advance.
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