linux-kernel - Re: [PATCH] ACPI: implement acpi_os_get

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Date:	Mon, 20 May 2013 13:25:30 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	linux-acpi@...r.kernel.org,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Len Brown <lenb@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ACPI: implement acpi_os_get_timer() according the spec

On Mon, May 13, 2013 at 02:44:32PM +0300, Mika Westerberg wrote:
> On Mon, May 13, 2013 at 01:38:46PM +0200, Rafael J. Wysocki wrote:
> > On Monday, May 13, 2013 01:27:51 PM Mika Westerberg wrote:
> > > ACPI Timer() opcode should return monotonically increasing clock with 100ns
> > > granularity. Implement this with the help of ktime_get().
> > > 
> > > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > 
> > That looks reasobable.  Have you tested it?
> 
> Very lightly. Basically I added some debug printks() between two
> successsive calls of Timer() and it seemed like it returned correct time.
> 
> It is certainly better than returning t+1 every time Timer() is called :)

I did somewhat better test for this. I added following ASL code:

	...
	Store(Timer, Local1)
	Sleep(10)
	Divide(Subtract(Timer, Local1), 10000,, Local1)
	Sleep(Local1)

	Store(Timer, Local1)
	Sleep(200)
	Divide(Subtract(Timer, Local1), 10000,, Local1)
	Sleep(Local1)

	Store(Timer, Local1)
	Sleep(1300)
	Divide(Subtract(Timer, Local1), 10000,, Local1)
	Sleep(Local1)

The second sleep should be pretty close to the first one.

Without this patch I get:

[   11.488100] ACPI: acpi_os_get_timer() TBD
[   11.492150] ACPI: Sleep(10)
[   11.502993] ACPI: Sleep(0)
[   11.506315] ACPI: Sleep(200)
[   11.706237] ACPI: Sleep(0)
[   11.709550] ACPI: Sleep(1300)
[   13.008929] ACPI: Sleep(0)

With the patch applied I get:

[   11.486786] ACPI: Sleep(10)
[   11.499029] ACPI: Sleep(12)
[   11.512350] ACPI: Sleep(200)
[   11.712282] ACPI: Sleep(200)
[   11.912170] ACPI: Sleep(1300)
[   13.211577] ACPI: Sleep(1300)

The above looks much more correct to me.
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