linux-kernel - Re: [PATCH 10/11] acpi: Export acpi_bus

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Message-ID: <1530202.t7e2q1JhJ2@vostro.rjw.lan>
Date:	Mon, 18 Jan 2016 23:46:18 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Lukas Wunner <lukas@...ner.de>
Cc:	Ankitprasad Sharma <ankitprasad.r.sharma@...el.com>,
	intel-gfx@...ts.freedesktop.org, akash.goel@...el.com,
	shashidhar.hiremath@...el.com, tvrtko.ursulin@...ux.intel.com,
	Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/11] acpi: Export acpi_bus_type

On Monday, January 18, 2016 11:39:07 PM Lukas Wunner wrote:
> Hi,
> 
> On Mon, Jan 18, 2016 at 11:28:27PM +0100, Rafael J. Wysocki wrote:
> > On Monday, January 18, 2016 03:57:29 PM Rafael J. Wysocki wrote:
> > > On Monday, January 18, 2016 02:31:00 PM Ankitprasad Sharma wrote:
> > > > On Fri, 2016-01-15 at 15:51 +0100, Rafael J. Wysocki wrote:
> > > > > On Thursday, January 14, 2016 11:46:46 AM ankitprasad.r.sharma@...el.com wrote:
> > > > > > From: Ankitprasad Sharma <ankitprasad.r.sharma@...el.com>
> > > > > > 
> > > > > > Some modules, like i915.ko, needs to detect when certain ACPI features
> > > > > > are active inorder to prevent corruption on contended resources.
> > > > > > In particular, use of BIOS RapidStart Technology may corrupt the contents
> > > > > > of the reserved graphics memory, due to unalarmed hibernation. In which
> > > > > > case i915.ko cannot assume that it (reserved gfx memory) remains
> > > > > > unmodified and must recreate teh contents and importantly not use it to
> > > > > > store unrecoverable user data.
> > > > > > 
> > > > > > Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@...el.com>
> > > > > > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> > > > > > Cc: Len Brown <lenb@...nel.org>
> > > > > > Cc: linux-acpi@...r.kernel.org
> > > > > > Cc: linux-kernel@...r.kernel.org
> > > > > > ---
> > > > > >  drivers/acpi/bus.c | 1 +
> > > > > >  1 file changed, 1 insertion(+)
> > > > > > 
> > > > > > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> > > > > > index a212cef..69509c7 100644
> > > > > > --- a/drivers/acpi/bus.c
> > > > > > +++ b/drivers/acpi/bus.c
> > > > > > @@ -814,6 +814,7 @@ struct bus_type acpi_bus_type = {
> > > > > >  	.remove		= acpi_device_remove,
> > > > > >  	.uevent		= acpi_device_uevent,
> > > > > >  };
> > > > > > +EXPORT_SYMBOL_GPL(acpi_bus_type);
> > > > > >  
> > > > > >  /* --------------------------------------------------------------------------
> > > > > >                               Initialization/Cleanup
> > > > > > 
> > > > > 
> > > > > No.
> > > > > 
> > > > > I see no reason whatsoever for doing this.
> > > > > 
> > > > > Thanks,
> > > > > Rafael
> > > > Hi Rafael,
> > > > 
> > > > Thanks for the response.
> > > > 
> > > > Can you please help me with, how to detect the presence of a certain
> > > > acpi device using its id (for example, INT3392 for Intel RST device)? 
> > > 
> > > If you want to check if the device ir present at all, you cen use
> > > acpi_device_is_present() introduced recently (although that would need
> > > to be exported if you want to use it from a driver).
> > 
> > I meant acpi_dev_present(), sorry about the mistake.
> > 
> > I guess we should rename it to acpi_device_found() or something similar
> > to avoid such confusion in the future.
> 
> The name was chosen because the PCI equivalent is called pci_dev_present()
> and I assumed that name already stuck in developers' heads, so if they're
> looking for an ACPI presence detection function, that's what they'd look
> for first.

But "present" in ACPI really means something different.  There may be ACPI
device objects in the namespace for devices that are not *actually* present.

Thanks,
Rafael