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

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Message-ID: <20170417210353.GA19771@roeck-us.net>
Date:   Mon, 17 Apr 2017 14:03:53 -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 08:40:38PM +0000, Moore, Robert wrote:
> 
> 
> > -----Original Message-----
> > From: Guenter Roeck [mailto:linux@...ck-us.net]
> > Sent: Monday, April 17, 2017 12:45 PM
> > 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
> > 
> > >
> [Moore, Robert] 
> 
> I'm not an expert on the _DLM method, but I would point you to the description section in the ACPI spec, 5.7.5 _DLM (DeviceLock Mutex).
> 

I did. However, not being an ACPI expert, that doesn't tell me anything.

Guenter

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