RE: [PATCH] ACPICA: Export mutex functions

Moore, Robert
2017-04-12T21:56:43Z

> -----Original Message-----
> From: Guenter Roeck [mailto:linux@roeck-us.net]
> Sent: Wednesday, April 12, 2017 2:23 PM
> To: Moore, Robert <robert.moore@intel.com>
> Cc: Zheng, Lv <lv.zheng@intel.com>; Wysocki, Rafael J
> <rafael.j.wysocki@intel.com>; Len Brown <lenb@kernel.org>; linux-
> acpi@vger.kernel.org; devel@acpica.org; linux-kernel@vger.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@roeck-us.net]
> > > Sent: Wednesday, April 12, 2017 8:13 AM
> > > To: Moore, Robert <robert.moore@intel.com>; Zheng, Lv
> > > <lv.zheng@intel.com>; Wysocki, Rafael J
> > > <rafael.j.wysocki@intel.com>; Len Brown <lenb@kernel.org>
> > > Cc: linux-acpi@vger.kernel.org; devel@acpica.org; linux-
> > > kernel@vger.kernel.org; Guenter Roeck <linux@roeck-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@roeck-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
> >