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Sender: Guenter Roeck <groeck7@gmail.com>
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Date: Tue, 9 Jan 2024 07:23:40 -0800
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Subject: Re: [PATCH v4 2/2] hwmon: (acpi_power_meter) Ensure IPMI space
 handler is ready on Dell systems
Content-Language: en-US
To: Kai-Heng Feng <kai.heng.feng@canonical.com>, jdelvare@suse.com
Cc: linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20240109041218.980674-1-kai.heng.feng@canonical.com>
 <20240109041218.980674-2-kai.heng.feng@canonical.com>
From: Guenter Roeck <linux@roeck-us.net>
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In-Reply-To: <20240109041218.980674-2-kai.heng.feng@canonical.com>
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On 1/8/24 20:12, Kai-Heng Feng wrote:
> The following error can be observed at boot:
> [    3.717920] ACPI Error: No handler for Region [SYSI] (00000000ab9e62c5) [IPMI] (20230628/evregion-130)
> [    3.717928] ACPI Error: Region IPMI (ID=7) has no handler (20230628/exfldio-261)
> 
> [    3.717936] No Local Variables are initialized for Method [_GHL]
> 
> [    3.717938] No Arguments are initialized for method [_GHL]
> 
> [    3.717940] ACPI Error: Aborting method \_SB.PMI0._GHL due to previous error (AE_NOT_EXIST) (20230628/psparse-529)
> [    3.717949] ACPI Error: Aborting method \_SB.PMI0._PMC due to previous error (AE_NOT_EXIST) (20230628/psparse-529)
> [    3.717957] ACPI: \_SB_.PMI0: _PMC evaluation failed: AE_NOT_EXIST
> 
> On Dell systems several methods of acpi_power_meter access variables in
> IPMI region [0], so wait until IPMI space handler is installed by
> acpi_ipmi and also wait until SMI is selected to make the space handler
> fully functional.
> 
> [0] https://www.dell.com/support/manuals/en-us/redhat-enterprise-linux-v8.0/rhel8_rn_pub/advanced-configuration-and-power-interface-acpi-error-messages-displayed-in-dmesg?guid=guid-0d5ae482-1977-42cf-b417-3ed5c3f5ee62
> 
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> ---
> v4:
>   - No change.
> 
> v3:
>   - Use helper.
>   - Use return value to print warning message.
> 
> v2:
>   - Use completion instead of request_module().
> 
>   drivers/hwmon/acpi_power_meter.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/hwmon/acpi_power_meter.c b/drivers/hwmon/acpi_power_meter.c
> index 703666b95bf4..33fb9626633d 100644
> --- a/drivers/hwmon/acpi_power_meter.c
> +++ b/drivers/hwmon/acpi_power_meter.c
> @@ -883,6 +883,12 @@ static int acpi_power_meter_add(struct acpi_device *device)
>   	strcpy(acpi_device_class(device), ACPI_POWER_METER_CLASS);
>   	device->driver_data = resource;
>   
> +	if (dmi_match(DMI_SYS_VENDOR, "Dell Inc.") &&
> +	    acpi_dev_get_first_match_dev("IPI0001", NULL, -1)) {
> +		if (acpi_wait_for_acpi_ipmi())
> +			dev_warn(&device->dev, "Waiting for ACPI IPMI timeout");
> +	}
> +

What a hack :-(.

This needs a comment in the driver explaining the rationale for this change, and
also a comment explaining why, for example, using late_initcall() does not help.

If CONFIG_IPMI_SI=n, acpi_wait_for_acpi_ipmi() will return 0, indicating success.
I can only imagine that this will result in a failure since the whole point
of this code is to wait until that driver is loaded. Please explain how and why
the code works with CONFIG_IPMI_SI=n. Similar, if the function returns an error,
I can not imagine how it would make sense to instantiate the driver. If it does
make sense to continue in this situation, a comment is needed in the code
describing the rationale.

Third, the new symbol is declared with CONFIG_ACPI, but defined with
CONFIG_IPMI_SI. I can not imagine how this would compile with CONFIG_ACPI=y
and CONFIG_IPMI_SI={m,n} and/or CONFIG_ACPI_IPMI={m,n}.

On top of that, IPMI_SI and ACPI_IPMI are is tristate, as is SENSORS_ACPI_POWER.
This means that SENSORS_ACPI_POWER=y combined with CONFIG_IPMI_SI={m,n} or
CONFIG_ACPI_IPMI={m,n} will result in a compile failure.

Please make sure that this code compiles with all possible symbol combinations.

Thanks,
Guenter

>   	res = read_capabilities(resource);
>   	if (res)
>   		goto exit_free;