netdev - Re: [PATCH v2] driver core: platform_bus: allow runtime override of dev_pm

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Date:	Wed, 25 Aug 2010 01:30:09 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Kevin Hilman <khilman@...prootsystems.com>
Cc:	linux-kernel@...r.kernel.org, Magnus Damm <magnus.damm@...il.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>, Paul Mundt <lethal@...ux-sh.org>,
	Magnus Damm <damm@...nsource.se>,
	Eric Miao <eric.y.miao@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v2] driver core: platform_bus: allow runtime override of dev_pm_ops

On Mon, Aug 23, 2010 at 11:18 AM, Kevin Hilman
<khilman@...prootsystems.com> wrote:
> Currently, the platform_bus allows customization of several of the
> busses dev_pm_ops methods by using weak symbols so that platform code
> can override them.  The weak-symbol approach is not scalable when
> wanting to support multiple platforms in a single kernel binary.
>
> Instead, provide __init methods for platform code to customize the
> dev_pm_ops methods at runtime.
>
> NOTE: after these dynamic methods are merged, the weak symbols should
>      be removed from drivers/base/platform.c.  AFAIK, this will only
>      affect SH and sh-mobile which should be converted to use this
>      runtime approach instead of the weak symbols.  After SH &
>      sh-mobile are converted, the weak symobols could be removed.
>
> Tested on OMAP3.
>
> Cc: Grant Likely <grant.likely@...retlab.ca>
> Cc: Magnus Damm <magnus.damm@...il.com>
> Signed-off-by: Kevin Hilman <khilman@...prootsystems.com>

Looks good to me.  A handful of nitpicks below, I don't know if Greg
will want you to respin for these or not.  Feel free to add my
acked-by line though:

Acked-by: Grant Likely <grant.likely@...retlab.ca>

> ---
>  drivers/base/platform.c         |   35 +++++++++++++++++++++++++++++++++++
>  include/linux/platform_device.h |    3 +++
>  2 files changed, 38 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index c6c933f..e40a773 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -976,6 +976,41 @@ struct bus_type platform_bus_type = {
>  };
>  EXPORT_SYMBOL_GPL(platform_bus_type);
>
> +/**
> + * platform_bus_get_pm_ops: return pointer to busses dev_pm_ops

Nit: first line of kerneldoc format should look like this:

/**
 * platform_bus_get_pm_ops() - return pointer to busses dev_pm_ops

> + *
> + * This function can be used by platform code to get the current
> + * set of dev_pm_ops functions used by the platform_bus_type.
> + */
> +const struct dev_pm_ops * __init platform_bus_get_pm_ops(void)
> +{
> +       return platform_bus_type.pm;
> +}
> +
> +/**
> + * platform_bus_set_pm_ops: update dev_pm_ops for the platform_bus_type
> + *
> + * @pm: pointer to new dev_pm_ops struct to be used for platform_bus_type
> + *
> + * Platform code can override the dev_pm_ops methods of
> + * platform_bus_type by using this function.  It is expected that
> + * platform code will first do a platform_bus_get_pm_ops(), then
> + * kmemdup it, then customize selected methods and pass a pointer to
> + * the new struct dev_pm_ops to this function.
> + *
> + * Since platform-specific code is customizing methods for *all*
> + * devices (not just platform-specific devices) it is expected that
> + * any custom overrides of these functions will keep existing behavior
> + * and simply extend it.  For example, any customization of the
> + * runtime PM methods should continue to call the pm_generic_*
> + * functions as the default ones do in addition to the
> + * platform-specific behavior.
> + */
> +void __init platform_bus_set_pm_ops(struct dev_pm_ops *pm)

nit: const struct dev_pm_ops would be appropriate

> +{
> +       platform_bus_type.pm = pm;
> +}
> +
>  int __init platform_bus_init(void)
>  {
>        int error;
> diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h
> index d7ecad0..cd55d39 100644
> --- a/include/linux/platform_device.h
> +++ b/include/linux/platform_device.h
> @@ -138,6 +138,9 @@ extern struct platform_device *platform_create_bundle(struct platform_driver *dr
>                                        struct resource *res, unsigned int n_res,
>                                        const void *data, size_t size);
>
> +extern const struct dev_pm_ops * __init platform_bus_get_pm_ops(void);
> +extern void __init platform_bus_set_pm_ops(struct dev_pm_ops *pm);

The __init annotations should only appear in the .c file, not the header.

Cheers,
g.
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