Re: [RFC PATCH v2 14/35] ACPI: Only enumerate enabled (or functional) devices

[Gavin Shan <gshan@xxxxxxxxxx>]

On 9/14/23 22:27, Jonathan Cameron wrote:
> On Wed, 13 Sep 2023 16:38:02 +0000
> James Morse <james.morse@xxxxxxx> 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@xxxxxxx>
> > ---
> > 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