linux-kernel - Re: [PATCH] ACPICA: Export mutex functions

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Message-ID: <20170417194527.GA16734@roeck-us.net>
Date:   Mon, 17 Apr 2017 12:45:27 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Moore, Robert" <robert.moore@...el.com>
Cc:     "Zheng, Lv" <lv.zheng@...el.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        'Len Brown' <lenb@...nel.org>,
        "'linux-acpi@...r.kernel.org'" <linux-acpi@...r.kernel.org>,
        "'devel@...ica.org'" <devel@...ica.org>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
        "Box, David E" <david.e.box@...el.com>
Subject: Re: [PATCH] ACPICA: Export mutex functions

On Mon, Apr 17, 2017 at 07:27:37PM +0000, Moore, Robert wrote:
> 
> > -----Original Message-----
> > From: Moore, Robert
> > Sent: Monday, April 17, 2017 10:13 AM
> > To: Guenter Roeck <linux@...ck-us.net>; Zheng, Lv <lv.zheng@...el.com>
> > Cc: Wysocki, Rafael J <rafael.j.wysocki@...el.com>; Len Brown
> > <lenb@...nel.org>; linux-acpi@...r.kernel.org; devel@...ica.org; linux-
> > kernel@...r.kernel.org
> > Subject: RE: [PATCH] ACPICA: Export mutex functions
> > 
> > There is a model for the drivers to directly acquire an AML mutex
> > object. That is why the acquire/release public interfaces were added to
> > ACPICA.
> > 
> > I forget all of the details, but the model was developed with MS and
> > others during the ACPI 6.0 timeframe.
> > 
> > 
> [Moore, Robert] 
> 
> 
> Here is the case where the OS may need to directly acquire an AML mutex:
> 
> From the ACPI spec:
> 
> 19.6.2 Acquire (Acquire a Mutex)
> 
> Note: For Mutex objects referenced by a _DLM object, the host OS may also contend for ownership.
> 
>From the context in the dsdt, and from description of expected use cases for
_DLM objects I can find, this is what the mutex is used for (to serialize
access to a resource on a low pin count serial interconnect, aka LPC).

What does that mean in practice ? That I am not supposed to use it because
it doesn't follow standard ACPI mutex declaration rules ?

Thanks,
Guenter

> 
> 
> 
> Other than this case, the OS/drivers should never need to directly acquire an AML mutex.
> Bob
>