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:

quoted

On Monday, January 18, 2016 03:57:29 PM Rafael J. Wysocki wrote:

quoted

On Monday, January 18, 2016 02:31:00 PM Ankitprasad Sharma wrote:

quoted

On Fri, 2016-01-15 at 15:51 +0100, Rafael J. Wysocki wrote:

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On Thursday, January 14, 2016 11:46:46 AM ankitprasad.r.sharma@intel.com wrote:

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From: Ankitprasad Sharma <redacted>

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 <redacted>
Cc: "Rafael J. Wysocki" <redacted>
Cc: Len Brown <lenb@kernel.org>
Cc: linux-acpi@vger.kernel.org
Cc: linux-kernel@vger.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