Re: [PATCH] ACPICA: Export mutex functions

Guenter Roeck
2017-04-13T00:55:21Z

On Wed, Apr 12, 2017 at 09:56:37PM +0000, Moore, Robert wrote:
>
>
> > -----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.
>

Puh, I am relieved ...

Thanks,
Guenter

>
> > 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
> > >