linux-kernel - Re: [PATCH 2/2] ACPI / platform: Initialize ACPI handles of platform devices in advance

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Date:	Mon, 19 Nov 2012 08:23:34 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jean Delvare <khali@...ux-fr.org>, ben-linux@...ff.org,
	w.sang@...gutronix.de, linux-kernel@...r.kernel.org,
	lenb@...nel.org, rafael.j.wysocki@...el.com,
	broonie@...nsource.wolfsonmicro.com, grant.likely@...retlab.ca,
	linus.walleij@...aro.org, mathias.nyman@...ux.intel.com,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH 2/2] ACPI / platform: Initialize ACPI handles of platform
 devices in advance

On Sun, Nov 18, 2012 at 10:13:59PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> The current platform device creation and registration code in
> acpi_create_platform_device() is quite convoluted.  This function
> takes an ACPI device node as an argument and eventually calls
> platform_device_register_resndata() to create and register a
> platform device object on the basis of the information contained
> in that code.  However, it doesn't associate the new platform
> device with the ACPI node directly, but instead it relies on
> acpi_platform_notify(), called from within device_add(), to find
> that ACPI node again with the help of acpi_platform_find_device()
> and acpi_platform_match() and then attach the new platform device
> to it.  This causes an additional ACPI namespace walk to happen and
> is clearly suboptimal.
> 
> Use the observation that it is now possible to initialize the ACPI
> handle of a device before calling device_add() for it to make this
> code more straightforward.  Namely, add a new field to struct
> platform_device_info allowing us to pass the ACPI handle of interest
> to platform_device_register_full(), which will then use it to
> initialize the new device's ACPI handle before registering it.
> This will cause acpi_platform_notify() to use the ACPI handle from
> the device structure directly instead of using the .find_device()
> routine provided by the device's bus type.  In consequence,
> acpi_platform_bus, acpi_platform_find_device(), and
> acpi_platform_match() are not necessary any more, so remove them.

Why can't you use the platform_data * that is already in struct device
for this, instead of adding an acpi-specific field to the
platform_device structure?

If not that, surely there is another field in struct device that you
could use that is free for this type of device?

>  struct platform_device_info {
>  		struct device *parent;
> +		void *acpi_handle;

Oh, and if I do accept this, I want a "real" structure pointer here
please, not a void * "handle".  That way is a slippery slope to the
Windows kernel programming style :)

thanks,

greg k-h
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