Date:	Mon, 28 Sep 2015 11:05:02 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Thierry Reding <thierry.reding@...il.com>,
	Eric Anholt <eric@...olt.net>
Cc:	dri-devel <dri-devel@...ts.freedesktop.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] driver-core: platform: Provide helpers for
 multi-driver modules

On Thu, Sep 24, 2015 at 7:02 PM, Thierry Reding
<thierry.reding@...il.com> wrote:
> From: Thierry Reding <treding@...dia.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@...uxfoundation.org>
> Signed-off-by: Thierry Reding <treding@...dia.com>

I raised this already on irc but let's do it here too for the record:
Eric Anholt has a very similar thing (but in drm only) with the
addition of also integrating with the component framework:

http://lists.freedesktop.org/archives/dri-devel/2015-September/090449.html

Having something that works for everyone (so includes msm and can be
used for vc4 too) would be great. Adding Eric.
-Daniel

> ---
>  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]);
> +       }
> +
> +       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
>
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel



-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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