linux-kernel - Re: [PATCH] ACPI / driver core: Store a device pointer in struct acpi_dev

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Date:	Mon, 11 Nov 2013 22:56:22 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Lan Tianyu <tianyu.lan@...el.com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Aaron Lu <aaron.lu@...el.com>,
	Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"Luck, Tony" <tony.luck@...el.com>
Subject: Re: [PATCH] ACPI / driver core: Store a device pointer in struct acpi_dev_node

On Monday, November 11, 2013 07:03:18 AM Greg Kroah-Hartman wrote:
> On Mon, Nov 11, 2013 at 02:45:39PM +0100, Rafael J. Wysocki wrote:
> > On Monday, November 11, 2013 09:21:40 AM Lan Tianyu wrote:
> > > On 2013年11月10日 08:58, Rafael J. Wysocki wrote:
> > > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > > 
> > > > Modify struct acpi_dev_node to contain a pointer to struct device
> > > > ambedded in the struct acpi_device associated with the given device
> > > > object (that is, its ACPI companion device) instead of an ACPI handle
> > > > corresponding to that struct acpi_device.  Introduce two new macros
> > > > for manipulating that pointer in a CONFIG_ACPI-safe way,
> > > > ACPI_COMPANION() and ACPI_COMPANION_SET(), and rework the
> > > > ACPI_HANDLE() macro to take the above changes into account.
> > > > Drop the ACPI_HANDLE_SET() macro entirely and rework its users to
> > > > use ACPI_COMPANION_SET() instead.  For some of them who used to
> > > > pass the result of acpi_get_child() directly to ACPI_HANDLE_SET()
> > > > introduce a helper routine acpi_preset_companion() doing an
> > > > equivalent thing.
> > > > 
> > > > The rationale for using a struct device pointer instead of a
> > > > struct acpi_device one as the member of struct acpi_dev_node is
> > > > that it allows device.h to avoid including linux/acpi.h which would
> > > > introduce quite a bit of compilation overhead for stuff that doesn't
> > > > care about ACPI.
> > > > In turn, moving the macros to linux/acpi.h forces
> > > > the stuff that does care about ACPI to include that file as
> > > > appropriate anyway.
> > > 
> > > How about declaring "struct acpi_device" in the device.h? This can help
> > > to use struct acpi_device without including linux/acpi.h.
> > > 
> > > struct iommu_ops and struct iommu_group have been used by the same way
> > > in the device.h.
> > 
> > Yes, they are.  Well, that appears to work too.
> > 
> > Updated patch is appended.  It also contains some fixes for problems reported
> > by the auto build system and it's been tested on x86-64 now, so it should be
> > reasonably close to final.
> > 
> > Thanks,
> > Rafael
> > 
> > 
> > ---
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > Subject: ACPI / driver core: Store an ACPI device pointer in struct acpi_dev_node
> > 
> > Modify struct acpi_dev_node to contain a pointer to struct acpi_device
> > associated with the given device object (that is, its ACPI companion
> > device) instead of an ACPI handle corresponding to it.  Introduce two
> > new macros for manipulating that pointer in a CONFIG_ACPI-safe way,
> > ACPI_COMPANION() and ACPI_COMPANION_SET(), and rework the
> > ACPI_HANDLE() macro to take the above changes into account.
> > Drop the ACPI_HANDLE_SET() macro entirely and rework its users to
> > use ACPI_COMPANION_SET() instead.  For some of them who used to
> > pass the result of acpi_get_child() directly to ACPI_HANDLE_SET()
> > introduce a helper routine acpi_preset_companion() doing an
> > equivalent thing.
> > 
> > The main motivation for doing this is that there are things
> > represented by struct acpi_device objects that don't have valid
> > ACPI handles (so called fixed ACPI hardware features, such as
> > power and sleep buttons) and we would like to create platform
> > device objects for them and "glue" them to their ACPI companions
> > in the usual way (which currently is impossible due to the
> > lack of valid ACPI handles).  However, there are more reasons
> > why it may be useful.
> > 
> > First, struct acpi_device pointers allow of much better type checking
> > than void pointers which are ACPI handles, so it should be more
> > difficult to write buggy code using modified struct acpi_dev_node
> > and the new macros.  Second, the change should help to reduce (over
> > time) the number of places in which the result of ACPI_HANDLE() is
> > passed to acpi_bus_get_device() in order to obtain a pointer to the
> > struct acpi_device associated with the given "physical" device,
> > because now that pointer is returned by ACPI_COMPANION() directly.
> > Finally, the change should make it easier to write generic code that
> > will build both for CONFIG_ACPI set and unset without adding explicit
> > compiler directives to it.
> > 
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Thanks!

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