linux-kernel - Re: [PATCH v3 1/4] ACPI: Support system notify handler via .sys

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Date:	Sat, 24 Nov 2012 23:07:31 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Toshi Kani <toshi.kani@...com>
Cc:	linux-acpi@...r.kernel.org, lenb@...nel.org,
	linux-kernel@...r.kernel.org, bhelgaas@...gle.com,
	isimatu.yasuaki@...fujitsu.com, liuj97@...il.com
Subject: Re: [PATCH v3 1/4] ACPI: Support system notify handler via .sys_notify

On Saturday, November 24, 2012 11:01:56 PM Rafael J. Wysocki wrote:
> On Thursday, November 08, 2012 01:23:44 PM Toshi Kani wrote:
> > Added a new .sys_notify interface, which allows ACPI drivers to
> > register their system-level (ex. hotplug) notify handlers through
> > their acpi_driver table.  This removes redundant ACPI namespace
> > walks from ACPI drivers for faster booting.
> > 
> > The global notify handler acpi_bus_notify() is called for all
> > system-level ACPI notifications, which then calls an appropriate
> > driver's handler if any.  ACPI drivers no longer need to register
> > or unregister driver's handler to each ACPI device object.  It also
> > supports dynamic ACPI namespace with LoadTable & Unload opcode
> > without any modification in ACPI drivers.
> > 
> > Added a common system notify handler acpi_bus_sys_notify(), which
> > allows ACPI drivers to set it to .sys_notify when this function is
> > fully implemented.
> 
> I don't really understand this.
> 
> > It removes functional conflict between driver's
> > notify handler and the global notify handler acpi_bus_notify().
> > 
> > Note that the changes maintain backward compatibility for ACPI
> > drivers.  Any drivers registered their hotplug handler through the
> > existing interfaces, such as acpi_install_notify_handler() and
> > register_acpi_bus_notifier(), will continue to work as before.
> 
> I really wouldn't like to add new callbacks to struct acpi_device_ops, because
> I'd like that whole thing to go away entirely eventually, along with struct
> acpi_driver.
> 
> Moreover, in this particular case, it really is not useful to have to define
> a struct acpi_driver so that one can register for receiving system
> notifications from ACPI.  It would be really nice if non-ACPI drivers, such
> as PCI or platform, could do that too.
> 
> Besides, acpi_os_execute_deferred() is always run on CPU0, because of some
> SMI-related peculiarity, which is not very efficient as far as the events
> handling is concerned, but we can improve the situation a bit by queing the
> execution of the registered handlers in a different workqueue.  Maybe it's
> worth considering if we're going to change this code anyway?
> 
> > Signed-off-by: Toshi Kani <toshi.kani@...com>
> > ---
> >  drivers/acpi/bus.c      | 64 ++++++++++++++++++++++++++++----------
> >  drivers/acpi/scan.c     | 83 +++++++++++++++++++++++++++++++++++++++++++++++++
> >  include/acpi/acpi_bus.h |  6 ++++
> >  3 files changed, 137 insertions(+), 16 deletions(-)
> > 
> > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> > index 07a20ee..b256bcf2 100644
> > --- a/drivers/acpi/bus.c
> > +++ b/drivers/acpi/bus.c
> > @@ -779,21 +779,16 @@ void unregister_acpi_bus_notifier(struct notifier_block *nb)
> >  EXPORT_SYMBOL_GPL(unregister_acpi_bus_notifier);
> >  
> >  /**
> > - * acpi_bus_notify
> > - * ---------------
> > - * Callback for all 'system-level' device notifications (values 0x00-0x7F).
> > + * acpi_bus_sys_notify: Common system notify handler
> > + *
> > + * ACPI drivers may specify this common handler to its sys_notify entry.
> > + * TBD: This handler is not implemented yet.
> >   */
> > -static void acpi_bus_notify(acpi_handle handle, u32 type, void *data)
> > +void acpi_bus_sys_notify(acpi_handle handle, u32 type, void *data)
> 
> This isn't used anywhere.  Are drivers supposed to use it?  If so, what about
> the BUS_CHECK and DEVICE_CHECK notifications?
> 
> >  {
> > -	struct acpi_device *device = NULL;
> > -	struct acpi_driver *driver;
> > -
> >  	ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Notification %#02x to handle %p\n",
> >  			  type, handle));
> >  
> > -	blocking_notifier_call_chain(&acpi_bus_notify_list,
> > -		type, (void *)handle);

By the way, there is exacly one user of this chain, which is dock.c.

What about convering that to something different and dropping the chain to
start with?

Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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