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Message-ID: <7b5f8dda-93c9-6338-15a5-acf76910c35b@redhat.com>
Date:   Mon, 18 Sep 2023 14:38:09 +1000
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Subject: Re: [RFC PATCH v2 14/35] ACPI: Only enumerate enabled (or functional)
 devices
Content-Language: en-US
To:     Jonathan Cameron <Jonathan.Cameron@Huawei.com>,
        James Morse <james.morse@arm.com>
Cc:     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,
        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>
 <20230913163823.7880-15-james.morse@arm.com>
 <20230914132732.00006908@Huawei.com>
From:   Gavin Shan <gshan@redhat.com>
In-Reply-To: <20230914132732.00006908@Huawei.com>
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On 9/14/23 22:27, Jonathan Cameron wrote:
> On Wed, 13 Sep 2023 16:38:02 +0000
> James Morse <james.morse@arm.com> wrote:
> 
>> Today the ACPI enumeration code 'visits' all devices that are present.
>>
>> This is a problem for arm64, where CPUs are always present, but not
>> always enabled. When a device-check occurs because the firmware-policy
>> has changed and a CPU is now enabled, the following error occurs:
>> | acpi ACPI0007:48: Enumeration failure
>>
>> This is ultimately because acpi_dev_ready_for_enumeration() returns
>> true for a device that is not enabled. The ACPI Processor driver
>> will not register such CPUs as they are not 'decoding their resources'.
>>
>> Change acpi_dev_ready_for_enumeration() to also check the enabled bit.
>> ACPI allows a device to be functional instead of maintaining the
>> present and enabled bit. Make this behaviour an explicit check with
>> a reference to the spec, and then check the present and enabled bits.
> 
> "and the" only applies if the functional route hasn't been followed
> "if not this case check the present and enabled bits."
> 
>> This is needed to avoid enumerating present && functional devices that
>> are not enabled.
>>
>> Signed-off-by: James Morse <james.morse@arm.com>
>> ---
>> If this change causes problems on deployed hardware, I suggest an
>> arch opt-in: ACPI_IGNORE_STA_ENABLED, that causes
>> acpi_dev_ready_for_enumeration() to only check the present bit.
>> ---
>>   drivers/acpi/device_pm.c    |  2 +-
>>   drivers/acpi/device_sysfs.c |  2 +-
>>   drivers/acpi/internal.h     |  1 -
>>   drivers/acpi/property.c     |  2 +-
>>   drivers/acpi/scan.c         | 23 +++++++++++++----------
>>   5 files changed, 16 insertions(+), 14 deletions(-)
>>
>> diff --git a/drivers/acpi/device_pm.c b/drivers/acpi/device_pm.c
>> index f007116a8427..76c38478a502 100644
>> --- a/drivers/acpi/device_pm.c
>> +++ b/drivers/acpi/device_pm.c
>> @@ -313,7 +313,7 @@ int acpi_bus_init_power(struct acpi_device *device)
>>   		return -EINVAL;
>>   
>>   	device->power.state = ACPI_STATE_UNKNOWN;
>> -	if (!acpi_device_is_present(device)) {
>> +	if (!acpi_dev_ready_for_enumeration(device)) {
>>   		device->flags.initialized = false;
>>   		return -ENXIO;
>>   	}
>> diff --git a/drivers/acpi/device_sysfs.c b/drivers/acpi/device_sysfs.c
>> index b9bbf0746199..16e586d74aa2 100644
>> --- a/drivers/acpi/device_sysfs.c
>> +++ b/drivers/acpi/device_sysfs.c
>> @@ -141,7 +141,7 @@ static int create_pnp_modalias(const struct acpi_device *acpi_dev, char *modalia
>>   	struct acpi_hardware_id *id;
>>   
>>   	/* Avoid unnecessarily loading modules for non present devices. */
>> -	if (!acpi_device_is_present(acpi_dev))
>> +	if (!acpi_dev_ready_for_enumeration(acpi_dev))
>>   		return 0;
>>   
>>   	/*
>> diff --git a/drivers/acpi/internal.h b/drivers/acpi/internal.h
>> index 866c7c4ed233..a1b45e345bcc 100644
>> --- a/drivers/acpi/internal.h
>> +++ b/drivers/acpi/internal.h
>> @@ -107,7 +107,6 @@ int acpi_device_setup_files(struct acpi_device *dev);
>>   void acpi_device_remove_files(struct acpi_device *dev);
>>   void acpi_device_add_finalize(struct acpi_device *device);
>>   void acpi_free_pnp_ids(struct acpi_device_pnp *pnp);
>> -bool acpi_device_is_present(const struct acpi_device *adev);
>>   bool acpi_device_is_battery(struct acpi_device *adev);
>>   bool acpi_device_is_first_physical_node(struct acpi_device *adev,
>>   					const struct device *dev);
>> diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
>> index 413e4fcadcaf..e03f00b98701 100644
>> --- a/drivers/acpi/property.c
>> +++ b/drivers/acpi/property.c
>> @@ -1418,7 +1418,7 @@ static bool acpi_fwnode_device_is_available(const struct fwnode_handle *fwnode)
>>   	if (!is_acpi_device_node(fwnode))
>>   		return false;
>>   
>> -	return acpi_device_is_present(to_acpi_device_node(fwnode));
>> +	return acpi_dev_ready_for_enumeration(to_acpi_device_node(fwnode));
>>   }
>>   
>>   static const void *
>> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
>> index 17ab875a7d4e..f898591ce05f 100644
>> --- a/drivers/acpi/scan.c
>> +++ b/drivers/acpi/scan.c
>> @@ -304,7 +304,7 @@ static int acpi_scan_device_check(struct acpi_device *adev)
>>   	int error;
>>   
>>   	acpi_bus_get_status(adev);
>> -	if (acpi_device_is_present(adev)) {
>> +	if (acpi_dev_ready_for_enumeration(adev)) {
>>   		/*
>>   		 * This function is only called for device objects for which
>>   		 * matching scan handlers exist.  The only situation in which
>> @@ -338,7 +338,7 @@ static int acpi_scan_bus_check(struct acpi_device *adev, void *not_used)
>>   	int error;
>>   
>>   	acpi_bus_get_status(adev);
>> -	if (!acpi_device_is_present(adev)) {
>> +	if (!acpi_dev_ready_for_enumeration(adev)) {
>>   		acpi_scan_device_not_enumerated(adev);
>>   		return 0;
>>   	}
>> @@ -1908,11 +1908,6 @@ static bool acpi_device_should_be_hidden(acpi_handle handle)
>>   	return true;
>>   }
>>   
>> -bool acpi_device_is_present(const struct acpi_device *adev)
>> -{
>> -	return adev->status.present || adev->status.functional;
>> -}
>> -
>>   static bool acpi_scan_handler_matching(struct acpi_scan_handler *handler,
>>   				       const char *idstr,
>>   				       const struct acpi_device_id **matchid)
>> @@ -2375,16 +2370,24 @@ EXPORT_SYMBOL_GPL(acpi_dev_clear_dependencies);
>>    * acpi_dev_ready_for_enumeration - Check if the ACPI device is ready for enumeration
>>    * @device: Pointer to the &struct acpi_device to check
>>    *
>> - * Check if the device is present and has no unmet dependencies.
>> + * Check if the device is functional or enabled and has no unmet dependencies.
>>    *
>> - * Return true if the device is ready for enumeratino. Otherwise, return false.
>> + * Return true if the device is ready for enumeration. Otherwise, return false.
>>    */
>>   bool acpi_dev_ready_for_enumeration(const struct acpi_device *device)
>>   {
>>   	if (device->flags.honor_deps && device->dep_unmet)
>>   		return false;
>>   
>> -	return acpi_device_is_present(device);
>> +	/*
>> +	 * ACPI 6.5's 6.3.7 "_STA (Device Status)" allows firmware to return
>> +	 * (!present && functional) for certain types of devices that should be
>> +	 * enumerated.
> 
> I'd call out the fact that enumeration isn't same as "device driver should be loaded"
> which is the thing that functional is supposed to indicate should not happen.
> 
>> +	 */
>> +	if (!device->status.present && !device->status.enabled)
> 
> In theory no need to check !enabled if !present
> "If bit [0] is cleared, then bit 1 must also be cleared (in other words, a device that is not present cannot be enabled)."
> We could report an ACPI bug if that's seen.  If that bug case is ignored this code can
> become the simpler.
> 
> 	if (device->status.present)
> 		return device->status_enabled;
> 	else
> 		return device->status.functional;
> 
> Or the following also valid here (as functional should be set for enabled present devices
> unless they failed diagnostics).
> 
> 	if (dev->status.functional)
> 		return true;
> 	return device->status.present && device->status.enabled;
> 
> On assumption we want to enumerate dead devices for debug purposes...
> 

I think it's worthy to include the words about the synchronization between present/enabled
bits into comments, outlined by Jonathan, to help readers to understand the code. Something
like below for the comments:

	/*
          * ACPI 6.5's 6.3.7 "_STA (Device Status)" allows firmware to return
	 * (!present && functional) for certain types of devices that should be
          * enumerated. Note that the enabled bit can't be set until the present
          * bit is set.
          */

> 
>> +		return device->status.functional;
>> +
>> +	return device->status.present && device->status.enabled;
> 
> 
>>   }
>>   EXPORT_SYMBOL_GPL(acpi_dev_ready_for_enumeration);
>>   


Thanks,
Gavin