PCI/NPEM: Add Native PCIe Enclosure Management support

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>

1 files changed, 35 insertions, 0 deletions

diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
index 94c00996e633..9751b413f3d6 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -740,6 +740,7 @@
 #define PCI_EXT_CAP_ID_DVSEC	0x23	/* Designated Vendor-Specific */
 #define PCI_EXT_CAP_ID_DLF	0x25	/* Data Link Feature */
 #define PCI_EXT_CAP_ID_PL_16GT	0x26	/* Physical Layer 16.0 GT/s */
+#define PCI_EXT_CAP_ID_NPEM	0x29	/* Native PCIe Enclosure Management */
 #define PCI_EXT_CAP_ID_PL_32GT  0x2A    /* Physical Layer 32.0 GT/s */
 #define PCI_EXT_CAP_ID_DOE	0x2E	/* Data Object Exchange */
 #define PCI_EXT_CAP_ID_MAX	PCI_EXT_CAP_ID_DOE
@@ -1121,6 +1122,40 @@
 #define  PCI_PL_16GT_LE_CTRL_USP_TX_PRESET_MASK		0x000000F0
 #define  PCI_PL_16GT_LE_CTRL_USP_TX_PRESET_SHIFT	4
 
+/* Native PCIe Enclosure Management */
+#define PCI_NPEM_CAP     0x04 /* NPEM capability register */
+#define  PCI_NPEM_CAP_CAPABLE     0x00000001 /* NPEM Capable */
+
+#define PCI_NPEM_CTRL    0x08 /* NPEM control register */
+#define  PCI_NPEM_CTRL_ENABLE     0x00000001 /* NPEM Enable */
+
+/*
+ * Native PCIe Enclosure Management indication bits and Reset command bit
+ * are corresponding for capability and control registers.
+ */
+#define  PCI_NPEM_CMD_RESET       0x00000002 /* Reset Command */
+#define  PCI_NPEM_IND_OK          0x00000004 /* OK */
+#define  PCI_NPEM_IND_LOCATE      0x00000008 /* Locate */
+#define  PCI_NPEM_IND_FAIL        0x00000010 /* Fail */
+#define  PCI_NPEM_IND_REBUILD     0x00000020 /* Rebuild */
+#define  PCI_NPEM_IND_PFA         0x00000040 /* Predicted Failure Analysis */
+#define  PCI_NPEM_IND_HOTSPARE    0x00000080 /* Hot Spare */
+#define  PCI_NPEM_IND_ICA         0x00000100 /* In Critical Array */
+#define  PCI_NPEM_IND_IFA         0x00000200 /* In Failed Array */
+#define  PCI_NPEM_IND_IDT         0x00000400 /* Device Type */
+#define  PCI_NPEM_IND_DISABLED    0x00000800 /* Disabled */
+#define  PCI_NPEM_IND_SPEC_0      0x01000000
+#define  PCI_NPEM_IND_SPEC_1      0x02000000
+#define  PCI_NPEM_IND_SPEC_2      0x04000000
+#define  PCI_NPEM_IND_SPEC_3      0x08000000
+#define  PCI_NPEM_IND_SPEC_4      0x10000000
+#define  PCI_NPEM_IND_SPEC_5      0x20000000
+#define  PCI_NPEM_IND_SPEC_6      0x40000000
+#define  PCI_NPEM_IND_SPEC_7      0x80000000
+
+#define PCI_NPEM_STATUS  0x0c /* NPEM status register */
+#define  PCI_NPEM_STATUS_CC       0x00000001 /* Command Completed */
+
 /* Data Object Exchange */
 #define PCI_DOE_CAP		0x04    /* DOE Capabilities Register */
 #define  PCI_DOE_CAP_INT_SUP			0x00000001  /* Interrupt Support */