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

From: Corey Minyard <minyard@acm.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Kai-Heng Feng <kai.heng.feng@canonical.com>,
	jdelvare@suse.com, linux@roeck-us.net,
	Len Brown <lenb@kernel.org>,
	Robert Moore <robert.moore@intel.com>,
	linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org,
	acpica-devel@lists.linux.dev
Subject: Re: [PATCH v3 1/2] ACPI: IPMI: Add helper to wait for when SMI is selected
Date: Thu, 4 Jan 2024 09:42:25 -0600	[thread overview]
Message-ID: <ZZbR4X6z9wkSESzD@mail.minyard.net> (raw)
In-Reply-To: <CAJZ5v0gNa7XvUo3B1srXaWBrWx+Bx=w=D7ddi-mqda8xBdWwCQ@mail.gmail.com>

On Thu, Jan 04, 2024 at 02:34:52PM +0100, Rafael J. Wysocki wrote:
> On Thu, Jan 4, 2024 at 3:48 AM Kai-Heng Feng
> <kai.heng.feng@canonical.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@canonical.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?

The IPMI driver can't be unloaded if it has a user.

I've been following this, but I know little about ACPI.  Beyond this
solution, the only other solution I could come up with was to start the
IPMI driver earlier.  But then you are in a chicken-and-egg situation
(https://dictionary.cambridge.org/dictionary/english/chicken-and-egg-situation).
Which was the reason for the SPMI table, but that's really kind of
useless for this, even if the SPMI table existed.

-corey

> 
> > +}
> > +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__*/
> > --
> 