linux-kernel - Re: [PATCH V3 1/3] x86/ioapic: Support hot-removal of IOAPICs present during boot

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Date:	Fri, 10 Jun 2016 11:43:04 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Rui Wang <rui.y.wang@...el.com>
Cc:	tglx@...utronix.de, rjw@...ysocki.net, tony.luck@...el.com,
	bhelgaas@...gle.com, linux-acpi@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 1/3] x86/ioapic: Support hot-removal of IOAPICs
 present during boot

On Wed, Jun 08, 2016 at 05:32:44PM +0800, Rui Wang wrote:
> v3: Previous versions break mips. This version fixes it.
> 
> IOAPICs present during system boot aren't added to ioapic_list,
> thus are unable to be hot-removed. Fix it by calling
> acpi_ioapic_add() during root bus enumeration.
> 
> Signed-off-by: Rui Wang <rui.y.wang@...el.com>
> ---
>  drivers/acpi/internal.h | 2 --
>  drivers/acpi/ioapic.c   | 7 ++++---
>  drivers/acpi/pci_root.c | 2 +-
>  drivers/pci/setup-bus.c | 7 ++++++-
>  include/linux/acpi.h    | 3 +++
>  5 files changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/acpi/internal.h b/drivers/acpi/internal.h
> index 9bb0773..bb567a7 100644
> --- a/drivers/acpi/internal.h
> +++ b/drivers/acpi/internal.h
> @@ -40,10 +40,8 @@ int acpi_sysfs_init(void);
>  void acpi_container_init(void);
>  void acpi_memory_hotplug_init(void);
>  #ifdef	CONFIG_ACPI_HOTPLUG_IOAPIC
> -int acpi_ioapic_add(struct acpi_pci_root *root);
>  int acpi_ioapic_remove(struct acpi_pci_root *root);
>  #else
> -static inline int acpi_ioapic_add(struct acpi_pci_root *root) { return 0; }
>  static inline int acpi_ioapic_remove(struct acpi_pci_root *root) { return 0; }
>  #endif
>  #ifdef CONFIG_ACPI_DOCK
> diff --git a/drivers/acpi/ioapic.c b/drivers/acpi/ioapic.c
> index ccdc8db..0f272e2 100644
> --- a/drivers/acpi/ioapic.c
> +++ b/drivers/acpi/ioapic.c
> @@ -189,16 +189,17 @@ exit:
>  	return AE_OK;
>  }
>  
> -int acpi_ioapic_add(struct acpi_pci_root *root)
> +int acpi_ioapic_add(acpi_handle root_handle)
>  {
>  	acpi_status status, retval = AE_OK;
>  
> -	status = acpi_walk_namespace(ACPI_TYPE_DEVICE, root->device->handle,
> +	status = acpi_walk_namespace(ACPI_TYPE_DEVICE, root_handle,
>  				     UINT_MAX, handle_ioapic_add, NULL,
> -				     root->device->handle, (void **)&retval);
> +				     root_handle, (void **)&retval);
>  
>  	return ACPI_SUCCESS(status) && ACPI_SUCCESS(retval) ? 0 : -ENODEV;
>  }
> +EXPORT_SYMBOL_GPL(acpi_ioapic_add);
>  
>  int acpi_ioapic_remove(struct acpi_pci_root *root)
>  {
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index ae3fe4e..53f5965 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -614,7 +614,7 @@ static int acpi_pci_root_add(struct acpi_device *device,
>  	if (hotadd) {
>  		pcibios_resource_survey_bus(root->bus);
>  		pci_assign_unassigned_root_bus_resources(root->bus);
> -		acpi_ioapic_add(root);
> +		acpi_ioapic_add(root->device->handle);
>  	}
>  
>  	pci_lock_rescan_remove();
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index 55641a3..0658921 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -25,6 +25,7 @@
>  #include <linux/ioport.h>
>  #include <linux/cache.h>
>  #include <linux/slab.h>
> +#include <linux/acpi.h>
>  #include "pci.h"
>  
>  unsigned int pci_flags;
> @@ -1779,8 +1780,12 @@ void __init pci_assign_unassigned_resources(void)
>  {
>  	struct pci_bus *root_bus;
>  
> -	list_for_each_entry(root_bus, &pci_root_buses, node)
> +	list_for_each_entry(root_bus, &pci_root_buses, node) {
>  		pci_assign_unassigned_root_bus_resources(root_bus);
> +#ifdef CONFIG_X86
> +		acpi_ioapic_add(ACPI_HANDLE(root_bus->bridge));
> +#endif

This seems like a strange place to call acpi_ioapic_add().  Your
object is to call acpi_ioapic_add() during root bus enumeration.

I assume we *can't* call acpi_ioapic_add() from acpi_pci_root_add() at
boot time, for some reason you'll explain.  But is there a reason we
have to call it from pci_assign_unassigned_resources() (where it
requires an ifdef) instead of from pcibios_assign_resources(), which
is already x86-specific?

In acpi_pci_root_add(), we have this:

  acpi_pci_root_add(...)
  {
    ...
    if (hotadd)
      acpi_ioapic_add(root);

So the obvious question is why don't we just remove the "if (hotadd)"
and call acpi_ioapic_add() always.

I'm sure the reason is some ordering problem, but we need a comment in
acpi_pci_root_add() about why the obvious solution doesn't work.

> +	}
>  }
>  
>  void pci_assign_unassigned_bridge_resources(struct pci_dev *bridge)
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 288fac5..3ed22df 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -262,6 +262,9 @@ int acpi_unmap_cpu(int cpu);
>  
>  #ifdef CONFIG_ACPI_HOTPLUG_IOAPIC
>  int acpi_get_ioapic_id(acpi_handle handle, u32 gsi_base, u64 *phys_addr);
> +int acpi_ioapic_add(acpi_handle root);
> +#else
> +static inline int acpi_ioapic_add(acpi_handle root) { return 0; }
>  #endif
>  
>  int acpi_register_ioapic(acpi_handle handle, u64 phys_addr, u32 gsi_base);
> -- 
> 1.8.3.1
> 
> --
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