Re: [PATCH v6] gpio: consumer: new virtual driver

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Thu, Aug 17, 2023 at 08:43:56PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> 
> The GPIO subsystem has a serious problem with undefined behavior and
> use-after-free bugs on hot-unplug of GPIO chips. This can be considered a
> corner-case by some as most GPIO controllers are enabled early in the
> boot process and live until the system goes down but most GPIO drivers
> do allow unbind over sysfs, many are loadable modules that can be (force)
> unloaded and there are also GPIO devices that can be dynamically detached,
> for instance CP2112 which is a USB GPIO expender.
> 
> Bugs can be triggered both from user-space as well as by in-kernel users.
> We have the means of testing it from user-space via the character device
> but the issues manifest themselves differently in the kernel.
> 
> This is a proposition of adding a new virtual driver - a configurable
> GPIO consumer that can be configured over configfs (similarly to
> gpio-sim).
> 
> The configfs interface allows users to create dynamic GPIO lookup tables
> that are registered with the GPIO subsystem. Every config group
> represents a consumer device. Every sub-group represents a single GPIO
> lookup. The device can work in three modes: just keeping the line
> active, toggling it every second or requesting its interrupt and
> reporting edges. Every lookup allows to specify the key, offset and
> flags as per the lookup struct defined in linux/gpio/machine.h.
> 
> The module together with gpio-sim allows to easily trigger kernel
> hot-unplug errors. A simple use-case is to create a simulated chip,
> setup the consumer to lookup one of its lines in 'monitor' mode, unbind
> the simulator, unbind the consumer and observe the fireworks in dmesg.
> 
> This driver is aimed as a helper in tackling the hot-unplug problem in
> GPIO as well as basis for future regression testing once the fixes are
> upstream.

...

> @@ -46,6 +46,7 @@ obj-$(CONFIG_GPIO_BT8XX)		+= gpio-bt8xx.o
>  obj-$(CONFIG_GPIO_CADENCE)		+= gpio-cadence.o
>  obj-$(CONFIG_GPIO_CLPS711X)		+= gpio-clps711x.o
>  obj-$(CONFIG_GPIO_SNPS_CREG)		+= gpio-creg-snps.o
> +obj-$(CONFIG_GPIO_CONSUMER)		+= gpio-consumer.o

Order?

>  obj-$(CONFIG_GPIO_CRYSTAL_COVE)		+= gpio-crystalcove.o
>  obj-$(CONFIG_GPIO_CS5535)		+= gpio-cs5535.o
>  obj-$(CONFIG_GPIO_DA9052)		+= gpio-da9052.o

...

> +		return dev_err_probe(dev, ret,
> +				     "Failed to read GPIO line names\n");

With one line it takes 83 characters (and note, that long before checkpatch
went for 100, the string literals at the end of a long line were accepted)...

...

> +				return dev_err_probe(dev, ret,
> +						"Failed to request GPIO line interrupt\n");

And here with broken indentation you got 91.
Can you be consistent?

(I prefer as you know less LoCs)

...

> +static ssize_t
> +gpio_consumer_lookup_config_drive_store(struct config_item *item,
> +					const char *page, size_t count)
> +{
> +	struct gpio_consumer_lookup *lookup = to_gpio_consumer_lookup(item);
> +	struct gpio_consumer_device *dev = lookup->parent;
> +
> +	guard(mutex)(&dev->lock);
> +
> +	if (gpio_consumer_device_is_live_unlocked(dev))
> +		return -EBUSY;
> +
> +	if (sysfs_streq(page, "push-pull")) {
> +		lookup->flags &= ~(GPIO_OPEN_DRAIN | GPIO_OPEN_SOURCE);
> +	} else if (sysfs_streq(page, "open-drain")) {
> +		lookup->flags &= ~GPIO_OPEN_SOURCE;
> +		lookup->flags |= GPIO_OPEN_DRAIN;
> +	} else if (sysfs_streq(page, "open-source")) {
> +		lookup->flags &= ~GPIO_OPEN_DRAIN;
> +		lookup->flags |= GPIO_OPEN_SOURCE;
> +	} else {

> +		count = -EINVAL;

Strictly speaking this is incorrect.
You need

	ssize_t ret;
	...
	ret = count;
	if (...)
		ret = -EINVAL;

> +	}
> +
> +	return count;
> +}

> +static ssize_t
> +gpio_consumer_lookup_config_pull_store(struct config_item *item,
> +				       const char *page, size_t count)
> +{

As per above.

> +}

...

> +		curr->chip_hwnum = lookup->offset < 0 ?
> +					U16_MAX : lookup->offset;

I found this way better

		curr->chip_hwnum =
			lookup->offset < 0 ? U16_MAX : lookup->offset;


...

> +	return ret ?: count;

Also possible way in the above mentioned cases.

...


I'm not going to bikeshed, I believe you can fix above accordingly,
either way

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

-- 
With Best Regards,
Andy Shevchenko