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

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Date:   Wed, 12 Apr 2017 14:22:41 -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>
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() ?

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
>