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The PCIe SSD Status LED Management _DSM defined in PCI Firmware Spec r3.3
sec 4.7 provides a way to manage LEDs via ACPI.
The design is similar to NPEM defined in PCIe Base Specification r6.1 sec
6.28:
- Both standards are indication oriented,
- _DSM supported bits correspond to NPEM capability register bits,
- _DSM control bits correspond to NPEM control register bits.
_DSM does not support enclosure-specific indications or the special NPEM
commands NPEM_ENABLE and NPEM_RESET.
_DSM is implemented as a second backend in NPEM driver. The backend used is
logged with info priority. The same sysfs interface is used for both NPEM
and _DSM.
According to spec, _DSM has higher priority, and availability of _DSM in
not limited to devices with NPEM support.
The Dell implementation of DSM uses acpi ipmi, which may not be available
immediately (in fact it may take up to 10s for this interface to be
available). It can determine if DSM is supported (GET_SUPPORTED_STATES_DSM
is working) but it cannot serve GET_STATE_DSM or SET_STATE_DSM commands in
this time.
From userspace application perspective (primarily configured by systemd
service) it is better to have not working but configured interface rather
than have it available after few seconds.
For that reason, npem->active_indications cache is now loaded lazily, i.e.
any GET or SET request want cache to be updated if it is not done yet.
Link: https://lore.kernel.org/r/20240904104848.23480-4-mariusz.tkaczyk@linux.intel.com
Suggested-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Stuart Hayes <stuart.w.hayes@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
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Native PCIe Enclosure Management (NPEM, PCIe r6.1 sec 6.28) allows managing
LEDs in storage enclosures. NPEM is indication oriented and it does not
give direct access to LEDs. Although each indication *could* represent an
individual LED, multiple indications could also be represented as a single,
multi-color LED or a single LED blinking in a specific interval. The
specification leaves that open.
Each enabled indication (capability register bit on) is represented as a
ledclass_dev which can be controlled through sysfs. For every ledclass
device only 2 brightness states are allowed: LED_ON (1) or LED_OFF (0).
This corresponds to the NPEM control register (Indication bit on/off).
Ledclass devices appear in sysfs as child devices (subdirectory) of PCI
device which has an NPEM Extended Capability and indication is enabled in
NPEM capability register. For example, these are LEDs created for pcieport
"10000:02:05.0" on my setup:
leds/
├── 10000:02:05.0:enclosure:fail
├── 10000:02:05.0:enclosure:locate
├── 10000:02:05.0:enclosure:ok
└── 10000:02:05.0:enclosure:rebuild
They can be also found in "/sys/class/leds" directory. The parent PCIe
device domain/bus/device/function address is used to guarantee uniqueness
across leds subsystem.
To enable/disable a "fail" indication, the "brightness" file can be edited:
echo 1 > ./leds/10000:02:05.0:enclosure:fail/brightness
echo 0 > ./leds/10000:02:05.0:enclosure:fail/brightness
PCIe r6.1, sec 7.9.19.2 defines the possible indications.
Multiple indications for same parent PCIe device can conflict and hardware
may update them when processing new request. To avoid issues, driver
refresh all indications by reading back control register.
This driver expects to be the exclusive NPEM extended capability manager.
It waits up to 1 second after imposing new request, it doesn't verify if
controller is busy before write, and it assumes the mutex lock gives
protection from concurrent updates.
If _DSM LED management is available, we assume the platform may be using
NPEM for its own purposes (see PCI Firmware Spec r3.3 sec 4.7), so the
driver does not use NPEM. A future patch will add _DSM support; an info
message notes whether NPEM or _DSM is being used.
NPEM is a PCIe extended capability so it should be registered in
pcie_init_capabilities() but it is not possible due to LED dependency. The
parent pci_device must be added earlier for led_classdev_register() to be
successful. NPEM does not require configuration on kernel side, so it is
safe to register LED devices later.
Link: https://lore.kernel.org/r/20240904104848.23480-3-mariusz.tkaczyk@linux.intel.com
Suggested-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Stuart Hayes <stuart.w.hayes@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
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