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

[Bjorn Helgaas <bhelgaas@google.com>]

On Sun, Dec 9, 2012 at 4:00 PM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.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.

Can you elaborate a bit on the complications in PCI enumeration?
Hopefully this will lead to some simplification in PCI enumeration,
but these patches don't go that far (yet).

> 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.

If I understand correctly, you're talking about a hierarchical
topology where a device, e.g., a bridge, can have subordinate devices
below it.

In general terms, if a driver claims X, and the driver's add() method
can assume that every device below X has already been registered, I
guess that means any bridge drivers must be integrated into the core,
so the core can enumerate things below the bridge without the driver's
help.  The PCI core effectively has the P2P bridge driver integrated
into it, so that's the way it is already for PCI.  I can imagine
scenarios, e.g., NTBs, where it's not practical to integrate the
bridge driver, so I'm not 100% comfortable with this assumption.  But
I admit that's a totally hypothetical situation, and there are lots of
other obstacles to non-integrated bridge drivers, like the fact that
we can't do dynamic resource assignment.

s/registerd/registered/ above

> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.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);
>  }
>
>  static int acpi_device_uevent(struct device *dev, struct kobj_uevent_env *env)
> @@ -1418,6 +1419,17 @@ static int acpi_bus_remove(struct acpi_d
>         return 0;
>  }
>
> +/*
> + * acpi_hot_add_bind - Bind _ADR-based devices on hot-add.
> + * @device: ACPI device node to bind.
> + */
> +static void acpi_hot_add_bind(struct acpi_device *device)
> +{
> +       if (device->flags.bus_address
> +           && device->parent && device->parent->ops.bind)
> +               device->parent->ops.bind(device);
> +}
> +
>  static int acpi_add_single_object(struct acpi_device **child,
>                                   acpi_handle handle, int type,
>                                   unsigned long long sta,
> @@ -1490,13 +1502,8 @@ static int acpi_add_single_object(struct
>
>         result = acpi_device_register(device);
>
> -       /*
> -        * Bind _ADR-Based Devices when hot add
> -        */
> -       if (device->flags.bus_address) {
> -               if (device->parent && device->parent->ops.bind)
> -                       device->parent->ops.bind(device);
> -       }
> +       if (device->bus_ops.acpi_op_match)
> +               acpi_hot_add_bind(device);
>
>  end:
>         if (!result) {
> @@ -1522,6 +1529,7 @@ static void acpi_bus_add_power_resource(
>         struct acpi_bus_ops ops = {
>                 .acpi_op_add = 1,
>                 .acpi_op_start = 1,
> +               .acpi_op_match = 1,
>         };
>         struct acpi_device *device = NULL;
>
> @@ -1574,9 +1582,9 @@ static acpi_status acpi_bus_check_add(ac
>                                       void *context, void **return_value)
>  {
>         struct acpi_bus_ops *ops = context;
> +       struct acpi_device *device = NULL;
>         int type;
>         unsigned long long sta;
> -       struct acpi_device *device;
>         acpi_status status;
>         int result;
>
> @@ -1600,48 +1608,77 @@ static acpi_status acpi_bus_check_add(ac
>          * We may already have an acpi_device from a previous enumeration.  If
>          * so, we needn't add it again, but we may still have to start it.
>          */
> -       device = NULL;
>         acpi_bus_get_device(handle, &device);
>         if (ops->acpi_op_add && !device) {
> -               acpi_add_single_object(&device, handle, type, sta, ops);
> -               /* Is the device a known good platform device? */
> -               if (device
> -                   && !acpi_match_device_ids(device, acpi_platform_device_ids))
> -                       acpi_create_platform_device(device);
> -       }
> +               struct acpi_bus_ops add_ops = *ops;
>
> -       if (!device)
> -               return AE_CTRL_DEPTH;
> -
> -       if (ops->acpi_op_start && !(ops->acpi_op_add)) {
> -               status = acpi_start_single_object(device);
> -               if (ACPI_FAILURE(status))
> +               add_ops.acpi_op_match = 0;
> +               acpi_add_single_object(&device, handle, type, sta, &add_ops);
> +               if (!device)
>                         return AE_CTRL_DEPTH;
> +
> +               device->bus_ops.acpi_op_match = 1;
>         }
>
>         if (!*return_value)
>                 *return_value = device;
> +
>         return AE_OK;
>  }
>
> +static acpi_status acpi_bus_probe_start(acpi_handle handle, u32 lvl,
> +                                       void *context, void **not_used)
> +{
> +       struct acpi_bus_ops *ops = context;
> +       struct acpi_device *device;
> +       acpi_status status = AE_OK;
> +
> +       if (acpi_bus_get_device(handle, &device))
> +               return AE_CTRL_DEPTH;
> +
> +       if (ops->acpi_op_add) {
> +               if (!acpi_match_device_ids(device, acpi_platform_device_ids)) {
> +                       /* This is a known good platform device. */
> +                       acpi_create_platform_device(device);
> +               } else {
> +                       int ret = device_attach(&device->dev);
> +                       acpi_hot_add_bind(device);
> +                       if (ret)
> +                               status = AE_CTRL_DEPTH;
> +               }
> +       } else if (ops->acpi_op_start) {
> +               if (ACPI_FAILURE(acpi_start_single_object(device)))
> +                       status = AE_CTRL_DEPTH;
> +       }
> +       return status;
> +}
> +
>  static int acpi_bus_scan(acpi_handle handle, struct acpi_bus_ops *ops,
>                          struct acpi_device **child)
>  {
> -       acpi_status status;
>         void *device = NULL;
> +       acpi_status status;
> +       int ret = 0;
>
>         status = acpi_bus_check_add(handle, 0, ops, &device);
> -       if (ACPI_SUCCESS(status))
> +       if (ACPI_FAILURE(status)) {
> +               ret = -ENODEV;
> +               goto out;
> +       }
> +
> +       acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX,
> +                           acpi_bus_check_add, NULL, ops, &device);
> +       if (device)
>                 acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX,
> -                                   acpi_bus_check_add, NULL, ops, &device);
> +                                   acpi_bus_probe_start, NULL, ops, NULL);
> +       else
> +               ret = -ENODEV;
>
> + out:
>         if (child)
>                 *child = device;
>
> -       if (device)
> -               return 0;
> -       else
> -               return -ENODEV;
> +       return ret;
>  }
>
>  /*
> @@ -1752,6 +1789,7 @@ static int acpi_bus_scan_fixed(void)
>         memset(&ops, 0, sizeof(ops));
>         ops.acpi_op_add = 1;
>         ops.acpi_op_start = 1;
> +       ops.acpi_op_match = 1;
>
>         /*
>          * Enumerate all fixed-feature devices.
>