linux-kernel - Re: [PATCH 1/6] ACPI: Separate adding ACPI device objects from probing ACPI drivers

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Date:	Wed, 12 Dec 2012 23:50:06 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>, Yinghai Lu <yinghai@...nel.org>
CC:	Bjorn Helgaas <bhelgaas@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	linux-pci@...r.kernel.org, Toshi Kani <toshi.kani@...com>,
	Myron Stowe <myron.stowe@...hat.com>
Subject: Re: [PATCH 1/6] ACPI: Separate adding ACPI device objects from probing
 ACPI drivers

On 12/10/2012 07:00 AM, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Currently, as soon as an ACPI device node object (struct acpi_device)
> is created, the driver core attempts to probe ACPI drivers against
> it.  That leads to some unpleasant side effects, like the fact that
> the boot code path for ACPI namespace scanning is different from the
> analogous hot-plug code path (during boot ACPI drivers are not
> present when ACPI device node objects are registered, so they are
> guaranteed not to be probed, which is not the case during hot-plug).
> That, in turn, leads to unnecessary complications in the PCI
> enumeration algorithm.
> 
> Reduce the differences between the boot and hot-plug cases by
> splitting the ACPI namespace scanning for devices into two passes,
> such that struct acpi_device objects are registerd in the first
> patch without probing ACPI drivers and the drivers are probed
> against them directly in the second pass.  This way ACPI drivers
> can assume that all of the ACPI device node objects in the given
> scope will be registered when their .add() routines run and the
> hot-plug case becomes the same as the boot case from their
> perspective.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/acpi/scan.c     |   96 +++++++++++++++++++++++++++++++++---------------
>  include/acpi/acpi_bus.h |    1 
>  2 files changed, 68 insertions(+), 29 deletions(-)
> 
> Index: linux/include/acpi/acpi_bus.h
> ===================================================================
> --- linux.orig/include/acpi/acpi_bus.h
> +++ linux/include/acpi/acpi_bus.h
> @@ -98,6 +98,7 @@ typedef void (*acpi_op_notify) (struct a
>  struct acpi_bus_ops {
>  	u32 acpi_op_add:1;
>  	u32 acpi_op_start:1;
> +	u32 acpi_op_match:1;
>  };
>  
>  struct acpi_device_ops {
> Index: linux/drivers/acpi/scan.c
> ===================================================================
> --- linux.orig/drivers/acpi/scan.c
> +++ linux/drivers/acpi/scan.c
> @@ -494,7 +494,8 @@ static int acpi_bus_match(struct device
>  	struct acpi_device *acpi_dev = to_acpi_device(dev);
>  	struct acpi_driver *acpi_drv = to_acpi_driver(drv);
>  
> -	return !acpi_match_device_ids(acpi_dev, acpi_drv->ids);
> +	return acpi_dev->bus_ops.acpi_op_match
> +		&& !acpi_match_device_ids(acpi_dev, acpi_drv->ids);
>  }
Hi Rafael,
	PCI host bridge hotplug has the same requirement to separate device
enumeration from device driver binding. And VFIO has a similar requirement too.
Yinghai and I have implemented two different solutions for PCI host bridge
hotplug but all rejected by Greg. So it would be great if we could promote
a common mechanism to the device core to temporarily disable binding drivers
to devices, which could used to support ACPI hotplug, PCI hotplug and VFIO.
Regards!
Gerry

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