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Message-ID: <c3ef8123-1fcc-7289-c475-c753de44d564@redhat.com>
Date:   Tue, 19 Sep 2023 10:31:17 +1000
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Subject: Re: [RFC PATCH v2 21/35] ACPI: Add post_eject to struct
 acpi_scan_handler for cpu hotplug
Content-Language: en-US
To:     James Morse <james.morse@arm.com>, linux-pm@vger.kernel.org,
        loongarch@lists.linux.dev, linux-acpi@vger.kernel.org,
        linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-riscv@lists.infradead.org, kvmarm@lists.linux.dev
Cc:     x86@kernel.org, Salil Mehta <salil.mehta@huawei.com>,
        Russell King <linux@armlinux.org.uk>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        jianyong.wu@arm.com, justin.he@arm.com
References: <20230913163823.7880-1-james.morse@arm.com>
 <20230913163823.7880-22-james.morse@arm.com>
From:   Gavin Shan <gshan@redhat.com>
In-Reply-To: <20230913163823.7880-22-james.morse@arm.com>
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On 9/14/23 02:38, James Morse 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.
> 

It's helpful to mention which ACPI processor driver needs to use _STA
to determine the status here. I guess the ACPI processor driver will
behave differently depending on the status.

> 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@arm.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(-)
> 

Reviewed-by: Gavin Shan <gshan@redhat.com>

> 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;

Thanks,
Gavin