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Date:   Fri, 20 Oct 2023 17:43:20 +0100
From:   Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To:     "Russell King (Oracle)" <linux@armlinux.org.uk>
CC:     James Morse <james.morse@arm.com>, <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>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        <jianyong.wu@arm.com>, <justin.he@arm.com>
Subject: Re: [RFC PATCH v2 14/35] ACPI: Only enumerate enabled (or
 functional) devices
Message-ID: <20231020174320.0000503c@Huawei.com>
In-Reply-To: <ZTKdgUu/wubKfdef@shell.armlinux.org.uk>
References: <20230913163823.7880-1-james.morse@arm.com>
        <20230913163823.7880-15-james.morse@arm.com>
        <20230914132732.00006908@Huawei.com>
        <20230914140940.00001417@Huawei.com>
        <ZTKdgUu/wubKfdef@shell.armlinux.org.uk>
Organization: Huawei Technologies Research and Development (UK) Ltd.
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On Fri, 20 Oct 2023 16:32:17 +0100
"Russell King (Oracle)" <linux@armlinux.org.uk> wrote:

> On Thu, Sep 14, 2023 at 02:09:40PM +0100, Jonathan Cameron wrote:
> > On Thu, 14 Sep 2023 13:27:32 +0100
> > Jonathan Cameron <Jonathan.Cameron@Huawei.com> 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...  
> > Actually ignore this.  Could have weird race with present, functional true,
> > but enabled not quite set - despite the device being there and self
> > tests having passed.  
> 
> Are you suggesting to ignore you're entire suggestion or just this
> suggestion and go with the first one?

I meant just the last one.  Sorry for confusion.

> 
> So, the code was originally effectively:
> 
> 	return adev->status.present || adev->status.functional;
> 
> So it has the truth table:
> 
> present	functional	result
> false	false		false
> false	true		true
> true	don't care	true
> 
> James' replacement code makes this:
> 
> 	if (!device->status.present && !device->status.enabled)
> 		return device->status.functional;
> 
> 	return device->status.present && device->status.enabled;
> 
> giving:
> 
> present	enabled	functional	result
> false	false	false		false
> false	false	true		true
> false	true	don't care	false	<== invalid according to spec
> true	false	don't care	false
> true	true	don't care	true
> 
> So, I think what you're getting at is that we want the logic to be
> according to the above table, but simplified, not caring about the
> invalid state too much?
> 
> In which case, I would suggest going with your first suggestion, in
> other words:
> 
> 	if (device->status.present)
> 		return device->status.enabled;
> 	else
> 		return device->status.functional;
> 
> Yes?
> 
Yes I agree.