Re: [PATCH 1/6] driver-core: platform: Provide helpers for multi-driver modules

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 24 Sep 2015, Thierry Reding <thierry.reding@gmail.com> wrote:
> From: Thierry Reding <treding@nvidia.com>
>
> Some modules register several sub-drivers. Provide a helper that makes
> it easy to register and unregister a list of sub-drivers, as well as
> unwind properly on error.
>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
>  Documentation/driver-model/platform.txt | 11 ++++++
>  drivers/base/platform.c                 | 60 +++++++++++++++++++++++++++++++++
>  include/linux/platform_device.h         |  5 +++
>  3 files changed, 76 insertions(+)
>
> diff --git a/Documentation/driver-model/platform.txt b/Documentation/driver-model/platform.txt
> index 07795ec51cde..e80468738ba9 100644
> --- a/Documentation/driver-model/platform.txt
> +++ b/Documentation/driver-model/platform.txt
> @@ -63,6 +63,17 @@ runtime memory footprint:
>  	int platform_driver_probe(struct platform_driver *drv,
>  			  int (*probe)(struct platform_device *))
>  
> +Kernel modules can be composed of several platform drivers. The platform core
> +provides helpers to register and unregister an array of drivers:
> +
> +	int platform_register_drivers(struct platform_driver * const *drivers,
> +				      unsigned int count);
> +	void platform_unregister_drivers(struct platform_driver * const *drivers,
> +					 unsigned int count);
> +
> +If one of the drivers fails to register, all drivers registered up to that
> +point will be unregistered in reverse order.
> +
>  
>  Device Enumeration
>  ~~~~~~~~~~~~~~~~~~
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index f80aaaf9f610..b7d7987fda97 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -711,6 +711,66 @@ err_out:
>  }
>  EXPORT_SYMBOL_GPL(__platform_create_bundle);
>  
> +/**
> + * platform_register_drivers - register an array of platform drivers
> + * @drivers: an array of drivers to register
> + * @count: the number of drivers to register
> + *
> + * Registers platform drivers specified by an array. On failure to register a
> + * driver, all previously registered drivers will be unregistered. Callers of
> + * this API should use platform_unregister_drivers() to unregister drivers in
> + * the reverse order.
> + *
> + * Returns: 0 on success or a negative error code on failure.
> + */
> +int platform_register_drivers(struct platform_driver * const *drivers,
> +			      unsigned int count)
> +{
> +	unsigned int i;
> +	int err;
> +
> +	for (i = 0; i < count; i++) {
> +		pr_debug("registering platform driver %ps\n", drivers[i]);
> +
> +		err = platform_driver_register(drivers[i]);
> +		if (err < 0) {
> +			pr_err("failed to register platform driver %ps: %d\n",
> +			       drivers[i], err);
> +			goto error;
> +		}
> +	}
> +
> +	return 0;
> +
> +error:
> +	while (i--) {
> +		pr_debug("unregistering platform driver %ps\n", drivers[i]);
> +		platform_driver_unregister(drivers[i]);
> +	}

This will call platform_driver_unregister() on the driver that failed,
but not the first driver.

You should probably make i an int, and use while (--i >= 0).

BR,
Jani.

> +
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(platform_register_drivers);
> +
> +/**
> + * platform_unregister_drivers - unregister an array of platform drivers
> + * @drivers: an array of drivers to unregister
> + * @count: the number of drivers to unregister
> + *
> + * Unegisters platform drivers specified by an array. This is typically used
> + * to complement an earlier call to platform_register_drivers(). Drivers are
> + * unregistered in the reverse order in which they were registered.
> + */
> +void platform_unregister_drivers(struct platform_driver * const *drivers,
> +				 unsigned int count)
> +{
> +	while (count--) {
> +		pr_debug("unregistering platform driver %ps\n", drivers[count]);
> +		platform_driver_unregister(drivers[count]);
> +	}
> +}
> +EXPORT_SYMBOL_GPL(platform_unregister_drivers);
> +
>  /* modalias support enables more hands-off userspace setup:
>   * (a) environment variable lets new-style hotplug events work once system is
>   *     fully running:  "modprobe $MODALIAS"
> diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h
> index bba08f44cc97..0c9f16bfdd99 100644
> --- a/include/linux/platform_device.h
> +++ b/include/linux/platform_device.h
> @@ -270,6 +270,11 @@ extern struct platform_device *__platform_create_bundle(
>  	struct resource *res, unsigned int n_res,
>  	const void *data, size_t size, struct module *module);
>  
> +int platform_register_drivers(struct platform_driver * const *drivers,
> +			      unsigned int count);
> +void platform_unregister_drivers(struct platform_driver * const *drivers,
> +				 unsigned int count);
> +
>  /* early platform driver interface */
>  struct early_platform_driver {
>  	const char *class_str;
> -- 
> 2.5.0
>
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-- 
Jani Nikula, Intel Open Source Technology Center