linux-kernel - Re: [PATCH v3 1/2] ACPI: IPMI: Add helper to wait for when SMI is selected

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Date: Thu, 4 Jan 2024 14:34:52 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc: jdelvare@...e.com, linux@...ck-us.net, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>, 
	Robert Moore <robert.moore@...el.com>, linux-acpi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, acpica-devel@...ts.linux.dev
Subject: Re: [PATCH v3 1/2] ACPI: IPMI: Add helper to wait for when SMI is selected

On Thu, Jan 4, 2024 at 3:48 AM Kai-Heng Feng
<kai.heng.feng@...onical.com> wrote:
>
> The function of acpi_power_meter module on Dell system requires IPMI
> handler is installed and SMI is selected.

Does the firmware use _DEP to let the OS know about this dependency?

> So add a helper to let acpi_power_meter know when IPMI handler and SMI
> are ready.
>
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
> v3:
>  - New patch.
>
>  drivers/acpi/acpi_ipmi.c | 17 ++++++++++++++++-
>  include/acpi/acpi_bus.h  |  5 +++++
>  2 files changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/acpi_ipmi.c b/drivers/acpi/acpi_ipmi.c
> index 0555f68c2dfd..54862cab7171 100644
> --- a/drivers/acpi/acpi_ipmi.c
> +++ b/drivers/acpi/acpi_ipmi.c
> @@ -23,6 +23,8 @@ MODULE_LICENSE("GPL");
>  #define IPMI_TIMEOUT                   (5000)
>  #define ACPI_IPMI_MAX_MSG_LENGTH       64
>
> +static struct completion smi_selected;
> +
>  struct acpi_ipmi_device {
>         /* the device list attached to driver_data.ipmi_devices */
>         struct list_head head;
> @@ -463,8 +465,10 @@ static void ipmi_register_bmc(int iface, struct device *dev)
>                 if (temp->handle == handle)
>                         goto err_lock;
>         }
> -       if (!driver_data.selected_smi)
> +       if (!driver_data.selected_smi) {
>                 driver_data.selected_smi = ipmi_device;
> +               complete(&smi_selected);
> +       }
>         list_add_tail(&ipmi_device->head, &driver_data.ipmi_devices);
>         mutex_unlock(&driver_data.ipmi_lock);
>
> @@ -578,10 +582,21 @@ acpi_ipmi_space_handler(u32 function, acpi_physical_address address,
>         return status;
>  }
>
> +int acpi_wait_for_acpi_ipmi(void)
> +{
> +       long ret;
> +
> +       ret = wait_for_completion_interruptible_timeout(&smi_selected, 2 * HZ);
> +
> +       return ret > 0 ? 0 : -ETIMEDOUT;

What will happen if the IPMI driver is unloaded after this has returned 0?

> +}
> +EXPORT_SYMBOL_GPL(acpi_wait_for_acpi_ipmi);
> +
>  static int __init acpi_ipmi_init(void)
>  {
>         int result;
>         acpi_status status;
> +       init_completion(&smi_selected);
>
>         if (acpi_disabled)
>                 return 0;
> diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> index 1216d72c650f..afa6e4d4bf46 100644
> --- a/include/acpi/acpi_bus.h
> +++ b/include/acpi/acpi_bus.h
> @@ -821,11 +821,16 @@ static inline void acpi_put_acpi_dev(struct acpi_device *adev)
>  {
>         acpi_dev_put(adev);
>  }
> +
> +int acpi_wait_for_acpi_ipmi(void);
> +
>  #else  /* CONFIG_ACPI */
>
>  static inline int register_acpi_bus_type(void *bus) { return 0; }
>  static inline int unregister_acpi_bus_type(void *bus) { return 0; }
>
> +static inline int acpi_wait_for_acpi_ipmi(void) { return 0; }
> +
>  #endif                         /* CONFIG_ACPI */
>
>  #endif /*__ACPI_BUS_H__*/
> --