Re: [PATCH 10/11] acpi: Export acpi_bus_type

[Ankitprasad Sharma]

On Mon, 2016-01-18 at 19:26 +0100, Lukas Wunner wrote:
Hi,
> Hi,
> 
> On Mon, Jan 18, 2016 at 03:57:29PM +0100, 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@xxxxxxxxx wrote:
> > > > > From: Ankitprasad Sharma <ankitprasad.r.sharma@xxxxxxxxx>
> > > > > 
> > > > > 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@xxxxxxxxx>
> > > > > Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> > > > > Cc: Len Brown <lenb@xxxxxxxxxx>
> > > > > Cc: linux-acpi@xxxxxxxxxxxxxxx
> > > > > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > > > > ---
> > > > >  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).
> 
> acpi_dev_present() is exported, so can be used in drivers just fine:
> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=2d12b6b381ba059d5f92798f5ea739672a2f5fcf
> 
> 
> > > As you might have seen (in the next patch in this series), that we use
> > > this symbol (acpi_bus_type) to iterate over all the devices registered
> > > on acpi bus, to check if there is a device with id INT3392 present or
> > > not.
> 
> Ankitprasad, just change your patch [11/11] thusly:
> 
> -       if (intel_detect_acpi_rst()) {
> +       if (acpi_dev_present("INT3392")) {
> 
> 
> Using bus_for_each_dev() was the wrong approach, most drivers call
> acpi_get_devices() to detect the presence of a particular HID,
> however that necessitates the definition of a callback in each driver,
> leading to lots of duplicate code. Hence the introduction of
> acpi_dev_present() which is also faster because it just iterates over
> a list instead of walking the namespace.
> 
> This new API landed in Linus' tree last Tuesday (PST), so you need
> to merge Linus' tree back into yours or wait until it gets merged
> into drm-intel-nightly.
> 
> Best regards,
> 
> Lukas

Thank you, Lukas/Rafael.

-Ankit