[RFC PATCH v2 21/35] ACPI: Add post_eject to struct acpi_scan_handler for cpu hotplug

[Jonathan Cameron]

On Wed, 13 Sep 2023 16:38:09 +0000
James Morse <james.morse at arm.com> wrote:

> struct acpi_scan_handler has a detach callback that is used to remove
> a driver when a bus is changed. When interacting with an eject-request,
> the detach callback is called before _EJ0.
> 
> This means the ACPI processor driver can't use _STA to determine if a
> CPU has been made not-present, or some of the other _STA bits have been
> changed. acpi_processor_remove() needs to know the value of _STA after
> _EJ0 has been called.

Why hasn't it been a problem before?

> 
> Add a post_eject callback to struct acpi_scan_handler. This is called
> after acpi_scan_hot_remove() has successfully called _EJ0. Because
> acpi_bus_trim_one() also clears the handler pointer, it needs to be
> told if the caller will go on to call acpi_bus_post_eject(), so
> that acpi_device_clear_enumerated() and clearing the handler pointer
> can be deferred. The existing not-used pointer is used for this.
> 
> Signed-off-by: James Morse <james.morse at arm.com>

I briefly wondered if an alternative model where you always call the
post walk was cleaner as the handler clear etc would always be in same place.
However, couldn't make it work that nicely because you still need to indicate
that it's an eject post handler or not which just moves the messy code.

As such this LGTM

Reviewed-by: Joanthan Cameron <Jonathan.Cameron at huawei.com>


> ---
>  drivers/acpi/acpi_processor.c |  4 +--
>  drivers/acpi/scan.c           | 52 ++++++++++++++++++++++++++++++-----
>  include/acpi/acpi_bus.h       |  1 +
>  3 files changed, 48 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index 22a15a614f95..00dcc23d49a8 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -459,7 +459,7 @@ static int acpi_processor_add(struct acpi_device *device,
>  
>  #ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU
>  /* Removal */
> -static void acpi_processor_remove(struct acpi_device *device)
> +static void acpi_processor_post_eject(struct acpi_device *device)
>  {
>  	struct acpi_processor *pr;
>  
> @@ -627,7 +627,7 @@ static struct acpi_scan_handler processor_handler = {
>  	.ids = processor_device_ids,
>  	.attach = acpi_processor_add,
>  #ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU
> -	.detach = acpi_processor_remove,
> +	.post_eject = acpi_processor_post_eject,
>  #endif
>  	.hotplug = {
>  		.enabled = true,
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index a675333618ae..b6d2f01640a9 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -244,18 +244,28 @@ static int acpi_scan_try_to_offline(struct acpi_device *device)
>  	return 0;
>  }
>  
> -static int acpi_bus_trim_one(struct acpi_device *adev, void *not_used)
> +/**
> + * acpi_bus_trim_one() - Detach scan handlers and drivers from ACPI device
> + *                       objects.
> + * @adev:       Root of the ACPI namespace scope to walk.
> + * @eject:      Pointer to a bool that indicates if this was due to an
> + *              eject-request.
> + *
> + * Must be called under acpi_scan_lock.
> + * If @eject points to true, clearing the device enumeration is deferred until
> + * acpi_bus_post_eject() is called.
> + */
> +static int acpi_bus_trim_one(struct acpi_device *adev, void *eject)
>  {
>  	struct acpi_scan_handler *handler = adev->handler;
> +	bool is_eject = *(bool *)eject;
>  
> -	acpi_dev_for_each_child_reverse(adev, acpi_bus_trim_one, NULL);
> +	acpi_dev_for_each_child_reverse(adev, acpi_bus_trim_one, eject);
>  
>  	adev->flags.match_driver = false;
>  	if (handler) {
>  		if (handler->detach)
>  			handler->detach(adev);
> -
> -		adev->handler = NULL;
>  	} else {
>  		device_release_driver(&adev->dev);
>  	}
> @@ -265,7 +275,12 @@ static int acpi_bus_trim_one(struct acpi_device *adev, void *not_used)
>  	 */
>  	acpi_device_set_power(adev, ACPI_STATE_D3_COLD);
>  	adev->flags.initialized = false;
> -	acpi_device_clear_enumerated(adev);
> +
> +	/* For eject this is deferred to acpi_bus_post_eject() */
> +	if (!is_eject) {
> +		adev->handler = NULL;
> +		acpi_device_clear_enumerated(adev);
> +	}
>  
>  	return 0;
>  }
> @@ -278,15 +293,36 @@ static int acpi_bus_trim_one(struct acpi_device *adev, void *not_used)
>   */
>  void acpi_bus_trim(struct acpi_device *adev)
>  {
> -	acpi_bus_trim_one(adev, NULL);
> +	bool eject = false;
> +
> +	acpi_bus_trim_one(adev, &eject);
>  }
>  EXPORT_SYMBOL_GPL(acpi_bus_trim);
>  
> +static int acpi_bus_post_eject(struct acpi_device *adev, void *not_used)
> +{
> +	struct acpi_scan_handler *handler = adev->handler;
> +
> +	acpi_dev_for_each_child_reverse(adev, acpi_bus_post_eject, NULL);
> +
> +	if (handler) {
> +		if (handler->post_eject)
> +			handler->post_eject(adev);
> +
> +		adev->handler = NULL;
> +	}
> +
> +	acpi_device_clear_enumerated(adev);
> +
> +	return 0;
> +}
> +
>  static int acpi_scan_hot_remove(struct acpi_device *device)
>  {
>  	acpi_handle handle = device->handle;
>  	unsigned long long sta;
>  	acpi_status status;
> +	bool eject = true;
>  
>  	if (device->handler && device->handler->hotplug.demand_offline) {
>  		if (!acpi_scan_is_offline(device, true))
> @@ -299,7 +335,7 @@ static int acpi_scan_hot_remove(struct acpi_device *device)
>  
>  	acpi_handle_debug(handle, "Ejecting\n");
>  
> -	acpi_bus_trim(device);
> +	acpi_bus_trim_one(device, &eject);
>  
>  	acpi_evaluate_lck(handle, 0);
>  	/*
> @@ -322,6 +358,8 @@ static int acpi_scan_hot_remove(struct acpi_device *device)
>  	} else if (sta & ACPI_STA_DEVICE_ENABLED) {
>  		acpi_handle_warn(handle,
>  			"Eject incomplete - status 0x%llx\n", sta);
> +	} else {
> +		acpi_bus_post_eject(device, NULL);
>  	}
>  
>  	return 0;
> diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> index 254685085c82..1b7e1acf925b 100644
> --- a/include/acpi/acpi_bus.h
> +++ b/include/acpi/acpi_bus.h
> @@ -127,6 +127,7 @@ struct acpi_scan_handler {
>  	bool (*match)(const char *idstr, const struct acpi_device_id **matchid);
>  	int (*attach)(struct acpi_device *dev, const struct acpi_device_id *id);
>  	void (*detach)(struct acpi_device *dev);
> +	void (*post_eject)(struct acpi_device *dev);
>  	void (*bind)(struct device *phys_dev);
>  	void (*unbind)(struct device *phys_dev);
>  	struct acpi_hotplug_profile hotplug;