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

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Message-ID: <94F2FBAB4432B54E8AACC7DFDE6C92E37E592822@ORSMSX110.amr.corp.intel.com>
Date:   Wed, 12 Apr 2017 21:56:37 +0000
From:   "Moore, Robert" <robert.moore@...el.com>
To:     Guenter Roeck <linux@...ck-us.net>
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>
Subject: RE: [PATCH] ACPICA: Export mutex functions



> -----Original Message-----
> From: Guenter Roeck [mailto:linux@...ck-us.net]
> Sent: Wednesday, April 12, 2017 2:23 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; devel@...ica.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] ACPICA: Export mutex functions
> 
> On Wed, Apr 12, 2017 at 03:29:55PM +0000, Moore, Robert wrote:
> > The ACPICA mutex functions are based on the host OS functions, so they
> don't really buy you anything. You should just use the native Linux
> functions.
> >
> 
> You mean they don't really acquire the requested ACPI mutex, and the
> underlying DSDT which declares and uses the mutex just ignores if the
> mutex was acquired by acpi_acquire_mutex() ?
> 
[Moore, Robert] 

OK, I understand now. Yes, these mutex interfaces are in fact intended for the purpose you mention:

* FUNCTION:    AcpiAcquireMutex
 *
 * PARAMETERS:  Handle              - Mutex or prefix handle (optional)
 *              Pathname            - Mutex pathname (optional)
 *              Timeout             - Max time to wait for the lock (millisec)
 *
 * RETURN:      Status
 *
 * DESCRIPTION: Acquire an AML mutex. This is a device driver interface to
 *              AML mutex objects, and allows for transaction locking between
 *              drivers and AML code. The mutex node is pointed to by
 *              Handle:Pathname. Either Handle or Pathname can be NULL, but
 *              not both.


And yes, both the acquire and release interfaces should be exported.





> To clarify: You are saying that code such as
> 
> 	acpi_status status;
> 
> 	status = acpi_acquire_mutex(NULL, "\\_SB.PCI0.SBRG.SIO1.MUT0",
> 0x10);
> 	if (ACPI_FAILURE(status)) {
> 		pr_err("Failed to acquire ACPI mutex\n");
> 		return -EBUSY;
> 	}
> 	...
> 
> when used in conjunction with
> 
> 	...
> 	Mutex (MUT0, 0x00)
> 	Method (ENFG, 1, NotSerialized)
> 	{
> 		Acquire (MUT0, 0x0FFF)
> 		...
> 	}
> 
> doesn't really provide exclusive access to the resource(s) protected by
> MUT0, even if acpi_acquire_mutex() returns ACPI_SUCCESS ?
> 
> Outch. Really ?
> 
> Thanks,
> Guenter
> 
> >
> > > -----Original Message-----
> > > From: Guenter Roeck [mailto:linux@...ck-us.net]
> > > Sent: Wednesday, April 12, 2017 8:13 AM
> > > To: Moore, Robert <robert.moore@...el.com>; Zheng, Lv
> > > <lv.zheng@...el.com>; Wysocki, Rafael J
> > > <rafael.j.wysocki@...el.com>; Len Brown <lenb@...nel.org>
> > > Cc: linux-acpi@...r.kernel.org; devel@...ica.org; linux-
> > > kernel@...r.kernel.org; Guenter Roeck <linux@...ck-us.net>
> > > Subject: [PATCH] ACPICA: Export mutex functions
> > >
> > > Mutex functions may be needed by drivers. Examples are accesses to
> > > Super-IO SIO registers (0x2e/0x2f or 0x4e/0x4f) or Super-IO
> > > environmental monitor registers, both which may also be accessed
> > > through DSDT.
> > >
> > > Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> > > ---
> > >  drivers/acpi/acpica/utxfmutex.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/drivers/acpi/acpica/utxfmutex.c
> > > b/drivers/acpi/acpica/utxfmutex.c index c016211c35ae..5d20581f4b2f
> > > 100644
> > > --- a/drivers/acpi/acpica/utxfmutex.c
> > > +++ b/drivers/acpi/acpica/utxfmutex.c
> > > @@ -150,6 +150,7 @@ acpi_acquire_mutex(acpi_handle handle,
> > > acpi_string pathname, u16 timeout)
> > >  	status = acpi_os_acquire_mutex(mutex_obj->mutex.os_mutex, timeout);
> > >  	return (status);
> > >  }
> > > +ACPI_EXPORT_SYMBOL(acpi_acquire_mutex)
> > >
> > >
> > > /*******************************************************************
> > > ****
> > > ********
> > >   *
> > > @@ -185,3 +186,4 @@ acpi_status acpi_release_mutex(acpi_handle
> > > handle, acpi_string pathname)
> > >  	acpi_os_release_mutex(mutex_obj->mutex.os_mutex);
> > >  	return (AE_OK);
> > >  }
> > > +ACPI_EXPORT_SYMBOL(acpi_release_mutex)
> > > --
> > > 2.7.4
> >