linux-kernel - Re: [PATCH] ACPI / scan: Always call acpi_bus

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Date:	Thu, 11 Jul 2013 02:39:55 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Toshi Kani <toshi.kani@...com>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Yinghai Lu <yinghai@...nel.org>
Subject: Re: [PATCH] ACPI / scan: Always call acpi_bus_scan() for bus check notifications

On Wednesday, July 10, 2013 05:48:26 PM Toshi Kani wrote:
> On Thu, 2013-07-11 at 00:45 +0200, Rafael J. Wysocki wrote:
> > On Wednesday, July 10, 2013 02:11:05 AM Rafael J. Wysocki wrote:
> > > On Tuesday, July 09, 2013 01:32:42 PM Toshi Kani wrote:
> > > > On Mon, 2013-07-08 at 02:10 +0200, Rafael J. Wysocki wrote:
> > > > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > > > 
> > > > > An ACPI_NOTIFY_BUS_CHECK notification means that we should scan the
> > > > > entire namespace starting from the given handle even if the device
> > > > > represented by that handle is present (other devices below it may
> > > > > just have been added).
> > > > > 
> > > > > For this reason, modify acpi_scan_bus_device_check() to always run
> > > > > acpi_bus_scan() if the notification being handled is of type
> > > > > ACPI_NOTIFY_BUS_CHECK.
> > > > > 
> > > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > > > Cc: 3.10+ <stable@...r.kernel.org>
> > > > 
> > > > Acked-by: Toshi Kani <toshi.kani@...com>
> > > > 
> > > > But, I think we need the additional patch below.
> > > 
> > > Yes, I think you're right.
> > 
> > That said I'd prefer to put the check into acpi_bus_device_attach() like in
> > the appended patch.
> 
> That's fine by me.  
> 
> Acked-by: Toshi Kani <toshi.kani@...com>
> 
> Just a minor point, though.  Isn't it a bit inconsistent with
> device_attach(), which checks dev->driver inside the function?

Well, device_attach() may be called from different places while this is
the only place where acpi_scan_attach_handler() is called.

The check in acpi_bus_device_attach() is easier to follow to me, because
it clearly means "we don't need to do anything more if there's a handler",
while the check in acpi_scan_attach_handler() makes you wonder "why do we
need to return 1 in that case?" and then you need to go to the caller and
look at the check of the return value to see "ah, because we don't want
that device_attach() to be called then!".

> That said, I am OK with either way.

Cool. :-)

Thanks,
Rafael


> > ---
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > Subject: ACPI / scan: Do not try to attach scan handlers to devices having them
> > 
> > In acpi_bus_device_attach(), if there is an ACPI device object
> > for the given handle and that device object has a scan handler
> > attached to it already, there's nothing more to do for that handle
> > and the function should just return success immediately.  Make
> > that happen.
> > 
> > Reported-by: Toshi Kani <toshi.kani@...com>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > ---
> >  drivers/acpi/scan.c |    3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > Index: linux-pm/drivers/acpi/scan.c
> > ===================================================================
> > --- linux-pm.orig/drivers/acpi/scan.c
> > +++ linux-pm/drivers/acpi/scan.c
> > @@ -1984,6 +1984,9 @@ static acpi_status acpi_bus_device_attac
> >  	if (acpi_bus_get_device(handle, &device))
> >  		return AE_CTRL_DEPTH;
> >  
> > +	if (device->handler)
> > +		return AE_OK;
> > +
> >  	ret = acpi_scan_attach_handler(device);
> >  	if (ret)
> >  		return ret > 0 ? AE_OK : AE_CTRL_DEPTH;
> > 
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
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> 
> 
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-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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