[2/2] PCI/NPEM: Add Native PCIe Enclosure Management support

Native PCIe Enclosure Management (NPEM, PCIe r6.1 sec 6.28) allows
managing LED blinking patterns in storage enclosures. NPEM is pattern
oriented and it does not give direct access to LED. Although each of
the patterns (register bits) *could* represent an individual LED, multiple
patterns 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 pattern is represented here as a ledclass_dev which can be controlled
through sysfs. For every LED only 2 brightness states are allowed:
LED_ON or LED_OFF. LED appears in sysfs as child device (subdirectory)
of PCI device which has an NPEM Extended Capability and LED's pattern
is enabled in NPEM capability register.

Definition of patterns are described in PCIE Base Specification r6.1[1].
The interface is ready to support enclosures where patterns are not
mutually exclusive, driver may clear other LEDs if they cannot be enabled
together.

Driver is projected to be 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, assuming that mutex lock gives protection
from concurrent updates. Driver is not be registered if _DSM led management
is available.

NPEM is PCIe extended capability so it should be registered in
pcie_init_capabilities() but it is not possible due to led dependency.
Parent pci_device must be added earlier for led_classdev_register()
to be successful. NPEM does not require configuration on kernel side, it
is safe to register led devices later.

Link: https://members.pcisig.com/wg/PCI-SIG/document/19849 [1]
Link: https://lore.kernel.org/linux-pci/cover.1643822289.git.stuart.w.hayes@gmail.com/
Link: https://lore.kernel.org/all/20210601203820.3647-1-stuart.w.hayes@gmail.com/
Suggested-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
---
 drivers/pci/Kconfig           |   7 +
 drivers/pci/Makefile          |   1 +
 drivers/pci/bus.c             |   1 +
 drivers/pci/npem.c            | 339 ++++++++++++++++++++++++++++++++++
 drivers/pci/pci.h             |   8 +
 drivers/pci/remove.c          |   1 +
 include/linux/pci.h           |   4 +
 include/uapi/linux/pci_regs.h |  34 ++++
 8 files changed, 395 insertions(+)
 create mode 100644 drivers/pci/npem.c

[+cc Stuart]

On Thu, Feb 15, 2024 at 03:23:45PM +0100, Mariusz Tkaczyk wrote:
> Native PCIe Enclosure Management (NPEM, PCIe r6.1 sec 6.28) allows
> managing LED blinking patterns in storage enclosures. NPEM is pattern
> oriented and it does not give direct access to LED. Although each of
> the patterns (register bits) *could* represent an individual LED, multiple
> patterns could also be represented as a single, multi-color LED or a
> single LED blinking in a specific interval. The specification leaves
> that open.

This is nice work, thank you!

I think everything here (commit log and code) should use "indication"
instead of "pattern." The spec doesn't use the word "pattern" in the
NPEM context except incidentally ("LED blink patterns are outside the
scope of the spec" and "LED Blink Patterns (e.g., IBPI)", whatever
that is).

Sec 7.9.19 refers to "indications," e.g., "OK indication," "Locate
indication," etc.  That's more generic and could certainly include the
alternatives you mention.  I think sec 6.28 should have used the
"indication" terminology as well to avoid the impression of LED
technology, individual LEDs per bit, blinking, etc.

> Each pattern is represented here as a ledclass_dev which can be controlled
> through sysfs. For every LED only 2 brightness states are allowed:
> LED_ON or LED_OFF. LED appears in sysfs as child device (subdirectory)
> of PCI device which has an NPEM Extended Capability and LED's pattern
> is enabled in NPEM capability register.

The NPEM Control register only specifies "indication ON" or
"indication OFF," so IIUC, this basically exposes each indication
("OK", "Locate", etc) as a separate ledclass_dev in sysfs, with LED_ON
corresponding to "indication ON".

There is not necessarily an individual LED for each ledclass_dev, but
setting an individual device to LED_ON sets the corresponding NPEM
Control bit, and it's up to the enclosure to turn on the indication,
whether that means an individual LED, an LED color, a blink pattern,
or even some non-visual indication.

Can we include a typical sysfs path and sample usage here?  Obviously
the intent is for userspace to control these indications.

> Definition of patterns are described in PCIE Base Specification r6.1[1].

I would agree with this if it said something like "PCIe r6.1, sec
7.9.19.2 defines the possible indications."  Looking for a definition
of "patterns" in the spec doesn't yield anything.

> The interface is ready to support enclosures where patterns are not
> mutually exclusive, driver may clear other LEDs if they cannot be enabled
> together.

I don't think this code does anything like "clearing other LEDs," does
it?  I agree that this code doesn't impose any constraints about
indications being mutually exclusive, etc.  It merely sets or clears
indication bits, and the hardware implementation is free to interpret
that as it sees fit.

> Driver is projected to be 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, assuming that mutex lock gives protection
> from concurrent updates. Driver is not be registered if _DSM led management
> is available.

s/is not be/is not/
s/led/LED/

> NPEM is PCIe extended capability so it should be registered in
> pcie_init_capabilities() but it is not possible due to led dependency.
> Parent pci_device must be added earlier for led_classdev_register()
> to be successful. NPEM does not require configuration on kernel side, it
> is safe to register led devices later.

s/NPEM is/NPEM is a/
s/led/LED/ (twice)

> Link: https://members.pcisig.com/wg/PCI-SIG/document/19849 [1]
> Link: https://lore.kernel.org/linux-pci/cover.1643822289.git.stuart.w.hayes@gmail.com/
> Link: https://lore.kernel.org/all/20210601203820.3647-1-stuart.w.hayes@gmail.com/
> Suggested-by: Lukas Wunner <lukas@wunner.de>
> Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
> ---
>  drivers/pci/Kconfig           |   7 +
>  drivers/pci/Makefile          |   1 +
>  drivers/pci/bus.c             |   1 +
>  drivers/pci/npem.c            | 339 ++++++++++++++++++++++++++++++++++
>  drivers/pci/pci.h             |   8 +
>  drivers/pci/remove.c          |   1 +
>  include/linux/pci.h           |   4 +
>  include/uapi/linux/pci_regs.h |  34 ++++
>  8 files changed, 395 insertions(+)
>  create mode 100644 drivers/pci/npem.c
> 
> diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
> index 74147262625b..127bcbed02c0 100644
> --- a/drivers/pci/Kconfig
> +++ b/drivers/pci/Kconfig
> @@ -138,6 +138,13 @@ config PCI_IOV
>  
>  	  If unsure, say N.
>  
> +config PCI_NPEM
> +	bool "Native PCIe Enclosure Management"
> +	depends on LEDS_CLASS
> +	help
> +	  Support for Native PCIe Enclosure Management. It allows managing LED
> +	  blinking patterns in storage enclosures.

s|managing LED blinking patterns|something about enclosure
indications, e.g., OK/Locate/Fail/etc|

>  config PCI_PRI
>  	bool "PCI PRI support"
>  	select PCI_ATS
> diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
> index cc8b4e01e29d..990d55826e5e 100644
> --- a/drivers/pci/Makefile
> +++ b/drivers/pci/Makefile
> @@ -33,6 +33,7 @@ obj-$(CONFIG_XEN_PCIDEV_FRONTEND) += xen-pcifront.o
>  obj-$(CONFIG_VGA_ARB)		+= vgaarb.o
>  obj-$(CONFIG_PCI_DOE)		+= doe.o
>  obj-$(CONFIG_PCI_DYNAMIC_OF_NODES) += of_property.o
> +obj-$(CONFIG_PCI_NPEM)		+= npem.o
>  
>  # Endpoint library must be initialized before its users
>  obj-$(CONFIG_PCI_ENDPOINT)	+= endpoint/
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index 826b5016a101..11bb8afe4eb8 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -345,6 +345,7 @@ void pci_bus_add_device(struct pci_dev *dev)
>  	if (pci_is_bridge(dev))
>  		of_pci_make_dev_node(dev);
>  	pci_create_sysfs_dev_files(dev);
> +	pci_npem_create(dev);
>  	pci_proc_attach_device(dev);
>  	pci_bridge_d3_update(dev);
>  
> diff --git a/drivers/pci/npem.c b/drivers/pci/npem.c
> new file mode 100644
> index 000000000000..005405b56cda
> --- /dev/null
> +++ b/drivers/pci/npem.c
> @@ -0,0 +1,339 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Native PCIe Enclosure Management
> + *	PCIe Base Specification r6.1 sec 6.28
> + *	PCIe Base Specification r6.1 sec 7.9.19
> + *
> + * Copyright (c) 2023 Intel Corporation
> + *	Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
> + */
> +#include <linux/acpi.h>
> +#include <linux/errno.h>
> +#include <linux/iopoll.h>
> +#include <linux/leds.h>
> +#include <linux/mutex.h>
> +#include <linux/pci.h>
> +#include <linux/pci_regs.h>
> +#include <linux/sysfs.h>
> +#include <linux/types.h>
> +#include <linux/uleds.h>
> +
> +#include "pci.h"
> +
> +/**
> + * struct npem_led - LED details.

Drop periods at end of these single line descriptions.

> + * @pattern: pattern details.
> + * @npem: npem device.
> + * @name: LED name.
> + * @led: LED device.
> + */
> +struct npem_led {
> +	const struct npem_pattern *pattern;
> +	struct npem *npem;
> +	char name[LED_MAX_NAME_SIZE];
> +	struct led_classdev led;
> +};
> +
> +/**
> + * struct npem - NPEM device properties.
> + * @dev: PCIe device with NPEM capability.
> + * @npem_lock: to keep concurrent updates synchronized.
> + * @pos: capability offset.
> + * @capabilities: capabilities register content.
> + * @control: control register content.
> + * @leds: available LEDs.
> + */
> +struct npem {
> +	struct pci_dev *dev;
> +	struct mutex npem_lock;
> +	u16 pos;
> +	u32 capabilities;
> +	u32 control;
> +	struct npem_led leds[];

Save led_cnt here so we have the size of leds[] and don't have to
verify that pci_npem_remove() will recompute the correct value.

> +};
> +
> +struct npem_pattern {

s/pattern/indication/

> +	u32 bit;
> +	char *name;
> +};
> +
> +static const struct npem_pattern patterns[] = {
> +	{PCI_NPEM_OK,		"enclosure:ok"},
> +	{PCI_NPEM_LOCATE,	"enclosure:locate"},
> +	{PCI_NPEM_FAIL,		"enclosure:fail"},
> +	{PCI_NPEM_REBUILD,	"enclosure:rebuild"},
> +	{PCI_NPEM_PFA,		"enclosure:pfa"},
> +	{PCI_NPEM_HOTSPARE,	"enclosure:hotspare"},
> +	{PCI_NPEM_ICA,		"enclosure:ica"},
> +	{PCI_NPEM_IFA,		"enclosure:ifa"},
> +	{PCI_NPEM_IDT,		"enclosure:idt"},
> +	{PCI_NPEM_DISABLED,	"enclosure:disabled"},
> +	{PCI_NPEM_SPEC_0,	"enclosure:specific_0"},
> +	{PCI_NPEM_SPEC_1,	"enclosure:specific_1"},
> +	{PCI_NPEM_SPEC_2,	"enclosure:specific_2"},
> +	{PCI_NPEM_SPEC_3,	"enclosure:specific_3"},
> +	{PCI_NPEM_SPEC_4,	"enclosure:specific_4"},
> +	{PCI_NPEM_SPEC_5,	"enclosure:specific_5"},
> +	{PCI_NPEM_SPEC_6,	"enclosure:specific_6"},
> +	{PCI_NPEM_SPEC_7,	"enclosure:specific_7"},
> +};
> +
> +#define for_each_npem_pattern(ptrn)\
> +	for (ptrn = patterns; ptrn < patterns + ARRAY_SIZE(patterns); ptrn++)
> +
> +/* Reserved bits are outside specification, count only defined bits. */
> +static int npem_get_supported_patterns_count(u32 capabilities)
> +{
> +	const struct npem_pattern *pattern;
> +	int cnt = 0;
> +
> +	for_each_npem_pattern(pattern)
> +		if (capabilities & pattern->bit)
> +			cnt++;
> +
> +	return cnt;
> +}
> +
> +static int npem_read_reg(struct npem *npem, u16 reg, u32 *val)
> +{
> +	int ret = pci_read_config_dword(npem->dev, npem->pos + reg, val);
> +
> +	return pcibios_err_to_errno(ret);
> +}
> +
> +static int npem_write_ctrl(struct npem *npem, u32 reg)
> +{
> +	int pos = npem->pos + PCI_NPEM_CTRL;
> +	int ret = pci_write_config_dword(npem->dev, pos, reg);
> +
> +	return pcibios_err_to_errno(ret);
> +}
> +
> +static int npem_set_active_patterns(struct npem *npem, u32 val)
> +{
> +	int ret, ret_val;
> +	u32 cc_status;
> +
> +	lockdep_assert_held(&npem->npem_lock);
> +
> +	/* This bit is always required */
> +	val |= PCI_NPEM_CTRL_ENABLED;
> +	ret = npem_write_ctrl(npem, val);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * For the case where a NPEM command has not completed immediately,
> +	 * it is recommended that software not continuously “spin” on polling
> +	 * the status register, but rather poll under interrupt at a reduced
> +	 * rate; for example at 10 ms intervals.
> +	 *
> +	 * PCIe r6.1 sec 6.28 "Implementation Note: Software Polling of NPEM
> +	 * Command Completed"

The implementation note also recommends reversing the order, i.e.,
polling for completion of previous command and then writing a new
command, but it looks like we don't use that strategy?

> +	 */
> +	ret = read_poll_timeout(npem_read_reg, ret_val,
> +				ret_val || (cc_status & PCI_NPEM_STATUS_CC),
> +				10 * USEC_PER_MSEC, USEC_PER_SEC, false, npem,
> +				PCI_NPEM_STATUS, &cc_status);
> +
> +	return ret ?: ret_val;
> +}
> +
> +static enum led_brightness npem_get(struct led_classdev *led)
> +{
> +	struct npem_led *nled = container_of(led, struct npem_led, led);
> +	u32 mask = nled->pattern->bit | PCI_NPEM_CTRL_ENABLED;
> +	struct npem *npem = nled->npem;
> +	int ret, val = 0;
> +
> +	ret = mutex_lock_interruptible(&npem->npem_lock);
> +	if (ret)
> +		return ret;
> +
> +	/* Pattern is ON if pattern and PCI_NPEM_CTRL_ENABLED bits are set */
> +	if ((npem->control & mask) == mask)
> +		val = 1;
> +
> +	mutex_unlock(&npem->npem_lock);
> +
> +	return val;
> +}
> +
> +int npem_set(struct led_classdev *led, enum led_brightness brightness)
> +{
> +	struct npem_led *nled = container_of(led, struct npem_led, led);
> +	struct npem *npem = nled->npem;
> +	u32 patterns;
> +	int ret;
> +
> +	ret = mutex_lock_interruptible(&npem->npem_lock);
> +	if (ret)
> +		return ret;
> +
> +	if (brightness == LED_OFF)
> +		patterns = npem->control & ~(nled->pattern->bit);
> +	else
> +		patterns = npem->control | nled->pattern->bit;
> +
> +	ret = npem_set_active_patterns(npem, patterns);
> +	if (ret == 0)
> +		/*
> +		 * Read register after write to keep cache in-sync. Controller
> +		 * may modify active bits, e.g. some patterns could be mutally
> +		 * exclusive.

s/mutally/mutually/

A citation for this would be helpful.  Sec 7.9.19.3 does say most NPEM
Control bits are permitted to be read-only zero, which would be one
case of modifying active bits.  But I think "mutually exclusive" is
stronger than that.

> +		 */
> +		ret = npem_read_reg(npem, PCI_NPEM_CTRL, &npem->control);
> +
> +	mutex_unlock(&npem->npem_lock);
> +	return ret;
> +}
> +
> +#define DSM_GUID GUID_INIT(0x5d524d9d, 0xfff9, 0x4d4b,  0x8c, 0xb7, 0x74, 0x7e,\
> +			   0xd5, 0x1e, 0x19, 0x4d)
> +#define GET_SUPPORTED_STATES_DSM	BIT(1)
> +#define GET_STATE_DSM			BIT(2)
> +#define SET_STATE_DSM			BIT(3)
> +
> +static bool npem_has_dsm(struct pci_dev *pdev)
> +{
> +	static const guid_t dsm_guid = DSM_GUID;
> +	acpi_handle handle;
> +
> +	handle = ACPI_HANDLE(&pdev->dev);
> +	if (!handle)
> +		return false;
> +
> +	if (acpi_check_dsm(handle, &dsm_guid, 0x1, GET_SUPPORTED_STATES_DSM |
> +			   GET_STATE_DSM | SET_STATE_DSM) == true)
> +		return true;
> +	return false;
> +}
> +
> +static int npem_set_led_classdev(struct npem *npem, struct npem_led *nled)
> +{
> +	struct led_classdev *led = &nled->led;
> +	struct led_init_data init_data = {};
> +	char *name = nled->name;
> +	int ret;
> +
> +	init_data.devicename = pci_name(npem->dev);
> +	init_data.default_label = nled->pattern->name;
> +
> +	ret = led_compose_name(&npem->dev->dev, &init_data, name);
> +	if (ret)
> +		return ret;
> +
> +	led->name = name;
> +	led->brightness_set_blocking = npem_set;
> +	led->brightness_get = npem_get;
> +	led->max_brightness = LED_ON;
> +	led->default_trigger = "none";
> +	led->flags = 0;
> +
> +	ret = led_classdev_register(&npem->dev->dev, led);
> +	if (ret)
> +		/* Clear the name to indicate that it is not registered. */
> +		name[0] = 0;
> +	return ret;
> +}
> +
> +void npem_free(struct npem *npem, int led_cnt)
> +{
> +	struct npem_led *nled;
> +	int cnt = 0;
> +
> +	while (cnt < led_cnt) {
> +		nled = &npem->leds[cnt++];
> +
> +		if (nled->name[0])
> +			led_classdev_unregister(&nled->led);
> +	}
> +
> +	mutex_destroy(&npem->npem_lock);
> +	kfree(npem);
> +}
> +
> +int npem_init(struct pci_dev *dev, int pos, u32 capabilities)

Can this be static?

> +{
> +	int led_cnt = npem_get_supported_patterns_count(capabilities);
> +	const struct npem_pattern *pattern;
> +	struct npem_led *nled;
> +	struct npem *npem;
> +	int led_idx = 0;
> +	int ret;
> +
> +	npem = kzalloc(sizeof(struct npem) + sizeof(struct npem_led) * led_cnt,
> +		       GFP_KERNEL);
> +	if (!npem)
> +		return -ENOMEM;
> +
> +	npem->pos = pos;
> +	npem->dev = dev;
> +	npem->capabilities = capabilities;
> +
> +	ret = npem_read_reg(npem, PCI_NPEM_CTRL, &npem->control);
> +	if (ret) {
> +		npem_free(npem, led_cnt);
> +		return ret;
> +	}
> +
> +	/*
> +	 * Do not take npem->npem_lock, get_brightness() is called on
> +	 * registration path.
> +	 */
> +	mutex_init(&npem->npem_lock);
> +
> +	for_each_npem_pattern(pattern) {
> +		if ((npem->capabilities & pattern->bit) == 0)
> +			/* Do not register not supported pattern */

s/not supported/unsupported/

> +			continue;
> +
> +		nled = &npem->leds[led_idx++];
> +		nled->pattern = pattern;
> +		nled->npem = npem;
> +
> +		ret = npem_set_led_classdev(npem, nled);
> +		if (ret) {
> +			npem_free(npem, led_cnt);
> +			return ret;
> +		}
> +	}
> +
> +	dev->npem = npem;
> +	return 0;
> +}
> +
> +void pci_npem_remove(struct pci_dev *dev)
> +{
> +	npem_free(dev->npem,
> +		  npem_get_supported_patterns_count(dev->npem->capabilities));
> +}
> +
> +void pci_npem_create(struct pci_dev *dev)
> +{
> +	int pos, ret;
> +	u32 cap;
> +
> +	if (!pci_is_pcie(dev))
> +		return;

Doesn't seem strictly required since we don't depend on any PCIe
features.

> +	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_NPEM);
> +	if (pos == 0)
> +		return;
> +
> +	if (pci_read_config_dword(dev, pos + PCI_NPEM_CAP, &cap) != 0 ||
> +	    (cap & PCI_NPEM_CAPABLE) == 0)
> +		return;
> +
> +	/*
> +	 * OS should use the DSM for LED control if it is available
> +	 * PCI Firmware Spec r3.3 sec 4.7.
> +	 */
> +	if (npem_has_dsm(dev))
> +		return;

Does Linux have support for this _DSM?  I don't see any, and I guess
this check means that if we have a device that supports NPEM on a
platform that supplies this _DSM, we can't use NPEM.

The stated intent of the _DSM (from the Feb 12, 2020 ECN at
https://members.pcisig.com/wg/PCI-SIG/document/14025) is to provide
NPEM-like functionality via an abstraction layer on top of NPEM, SES,
or other implementations.

The _DSM also gives the platform a chance to intercept and change or
reject indications requested by OSPM, although that isn't mentioned as
part of the intent.

I'm interested in your thoughts about this.  One possibility would be
to omit this check for now and add it back when the _DSM is supported,
so we could use NPEM directly when advertised by a device.  Or we
could keep this as-is and prohibit use of NPEM if the _DSM exists,
even though we know how to operate it.

> +	ret = npem_init(dev, pos, cap);
> +	if (ret)
> +		pci_err(dev, "Failed to register Native PCIe Enclosure Management, err: %d\n",
> +			ret);
> +}
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index e9750b1b19ba..6f79b1e5ee57 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -327,6 +327,14 @@ static inline void pci_doe_destroy(struct pci_dev *pdev) { }
>  static inline void pci_doe_disconnected(struct pci_dev *pdev) { }
>  #endif
>  
> +#ifdef CONFIG_PCI_NPEM
> +void pci_npem_create(struct pci_dev *dev);
> +void pci_npem_remove(struct pci_dev *dev);
> +#else
> +static inline void pci_npem_create(struct pci_dev *dev) { }
> +static inline void pci_npem_remove(struct pci_dev *dev) { }
> +#endif
> +
>  /**
>   * pci_dev_set_io_state - Set the new error state if possible.
>   *
> diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
> index d749ea8250d6..f2a346802f35 100644
> --- a/drivers/pci/remove.c
> +++ b/drivers/pci/remove.c
> @@ -20,6 +20,7 @@ static void pci_stop_dev(struct pci_dev *dev)
>  	if (pci_dev_is_added(dev)) {
>  
>  		device_release_driver(&dev->dev);
> +		pci_npem_remove(dev);
>  		pci_proc_detach_device(dev);
>  		pci_remove_sysfs_dev_files(dev);
>  		of_pci_remove_node(dev);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 7ab0d13672da..13cbbfb80963 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -516,6 +516,10 @@ struct pci_dev {
>  #ifdef CONFIG_PCI_DOE
>  	struct xarray	doe_mbs;	/* Data Object Exchange mailboxes */
>  #endif
> +#ifdef CONFIG_PCI_NPEM
> +	struct npem *npem;

Indent to match surrounding code.  Add comment to expand "NPEM".

> +#endif
> +
>  	u16		acs_cap;	/* ACS Capability offset */
>  	phys_addr_t	rom;		/* Physical address if not from BAR */
>  	size_t		romlen;		/* Length if not from BAR */
> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> index a39193213ff2..5ff3190da159 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
> @@ -1148,4 +1149,37 @@
>  #define PCI_DOE_DATA_OBJECT_DISC_RSP_3_PROTOCOL		0x00ff0000
>  #define PCI_DOE_DATA_OBJECT_DISC_RSP_3_NEXT_INDEX	0xff000000
>  
> +/* Native PCIe Enclosure Management */
> +#define PCI_NPEM_CAP	0x04 /* NPEM capability register */
> +#define	 PCI_NPEM_CAPABLE		0x01	/* NPEM Capable */

Update name to include "PCI_NPEM_CAP_*" to disambiguate.
Extend bitmask to suggest 32-bit register width, i.e., 0x00000001.

> +#define PCI_NPEM_CTRL	0x08 /* NPEM control register */
> +#define	 PCI_NPEM_CTRL_ENABLED		0x01	/* NPEM Enabled */

s/ENABLED/ENABLE/ to match spec name.  Extend bitmask to 32 bit width.

> +#define PCI_NPEM_STATUS	0x0c /* NPEM status register */
> +#define	 PCI_NPEM_STATUS_CC		0x01 /* NPEM Command completed */
> +/*
> + * Native PCIe Enclosure Management patterns and enclosure specific
> + * bits are corresponding for capability and control registers
> + */
> +#define  PCI_NPEM_RESET			0x0001 /* NPEM Reset Command */
> +#define  PCI_NPEM_OK			0x0004 /* NPEM pattern OK */
> +#define  PCI_NPEM_LOCATE		0x0008 /* NPEM pattern Locate */
> +#define  PCI_NPEM_FAIL			0x0010 /* NPEM pattern Fail */
> +#define  PCI_NPEM_REBUILD		0x0020 /* NPEM pattern Rebuild */
> +#define  PCI_NPEM_PFA			0x0040 /* NPEM pattern Predicted Failure Analysis */
> +#define  PCI_NPEM_HOTSPARE		0x0080 /* NPEM pattern Hot Spare */
> +#define  PCI_NPEM_ICA			0x0100 /* NPEM pattern In Critical Array */
> +#define  PCI_NPEM_IFA			0x0200 /* NPEM pattern In Failed Array */
> +#define  PCI_NPEM_IDT			0x0400 /* NPEM pattern Invalid Device Type */
> +#define  PCI_NPEM_DISABLED		0x0800 /* NPEM pattern Disabled */

Extend to 32 bits to match register width and the ones below.  Drop
"pattern" from these comments.

> +#define  PCI_NPEM_SPEC_0		0x00800000
> +#define  PCI_NPEM_SPEC_1		0x01000000
> +#define  PCI_NPEM_SPEC_2		0x02000000
> +#define  PCI_NPEM_SPEC_3		0x04000000
> +#define  PCI_NPEM_SPEC_4		0x08000000
> +#define  PCI_NPEM_SPEC_5		0x10000000
> +#define  PCI_NPEM_SPEC_6		0x20000000
> +#define  PCI_NPEM_SPEC_7		0x40000000

Could use "PCI_NPEM_IND_*" (for "indication") as used in sec 7.9.19.2
and .3.

Bjorn

On Wed, Mar 06, 2024 at 04:40:08PM -0600, Bjorn Helgaas wrote:
> On Thu, Feb 15, 2024 at 03:23:45PM +0100, Mariusz Tkaczyk wrote:
> > The interface is ready to support enclosures where patterns are not
> > mutually exclusive, driver may clear other LEDs if they cannot be enabled
> > together.
> 
> I don't think this code does anything like "clearing other LEDs," does
> it?  I agree that this code doesn't impose any constraints about
> indications being mutually exclusive, etc.  It merely sets or clears
> indication bits, and the hardware implementation is free to interpret
> that as it sees fit.

I guess the paragraph needs to be rephrased.  The point is that
if this NPEM driver sets bit A and another bit B is already set,
and the hardware is incapable of lighting up whatever is controlled
by these two bits *simultaneously*, the hardware might clear bit B
when setting bit A.  The driver can cope with that because
npem_set() reads back the register contents with npem_read_reg()
after calling npem_set_active_patterns().


> > +	/*
> > +	 * For the case where a NPEM command has not completed immediately,
> > +	 * it is recommended that software not continuously ???spin??? on polling
> > +	 * the status register, but rather poll under interrupt at a reduced
> > +	 * rate; for example at 10 ms intervals.
> > +	 *
> > +	 * PCIe r6.1 sec 6.28 "Implementation Note: Software Polling of NPEM
> > +	 * Command Completed"
> 
> The implementation note also recommends reversing the order, i.e.,
> polling for completion of previous command and then writing a new
> command, but it looks like we don't use that strategy?

I think the leds subsystem expects the LED to be lit up by the time
the ->brightness_set_blocking() callback returns.  If the driver waited
for command completion *before* setting a bit instead of afterwards,
it could happen that npem_set() (the ->brightness_set_blocking() callback)
returns even though the command hasn't completed yet and the LED thus
isn't lit up yet.

Thanks,

Lukas

On Wed, 6 Mar 2024 16:40:08 -0600
Bjorn Helgaas <helgaas@kernel.org> wrote:
 
> > +	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_NPEM);
> > +	if (pos == 0)
> > +		return;
> > +
> > +	if (pci_read_config_dword(dev, pos + PCI_NPEM_CAP, &cap) != 0 ||
> > +	    (cap & PCI_NPEM_CAPABLE) == 0)
> > +		return;
> > +
> > +	/*
> > +	 * OS should use the DSM for LED control if it is available
> > +	 * PCI Firmware Spec r3.3 sec 4.7.
> > +	 */
> > +	if (npem_has_dsm(dev))
> > +		return;  
> 
> Does Linux have support for this _DSM?  I don't see any, and I guess
> this check means that if we have a device that supports NPEM on a
> platform that supplies this _DSM, we can't use NPEM.

No, Linux doesn't support _DSM. It was proposed in previous iterations by Stuart
but I dropped it. We decided that it need to be strongly rebuild because
"pci/pcie" is not right place for ACPI code so we cannot register _DSM
driver instead of NPEM as it was proposed and I don't have _DSM capable
hardware to test it.

> 
> The stated intent of the _DSM (from the Feb 12, 2020 ECN at
> https://members.pcisig.com/wg/PCI-SIG/document/14025) is to provide
> NPEM-like functionality via an abstraction layer on top of NPEM, SES,
> or other implementations.
> 
> The _DSM also gives the platform a chance to intercept and change or
> reject indications requested by OSPM, although that isn't mentioned as
> part of the intent.
> 
> I'm interested in your thoughts about this.  One possibility would be
> to omit this check for now and add it back when the _DSM is supported,
> so we could use NPEM directly when advertised by a device.  Or we
> could keep this as-is and prohibit use of NPEM if the _DSM exists,
> even though we know how to operate it.

I decided to implement it 2nd way because I don't know if I can use NPEM if
_DSM is implemented, I mean that hardware may do not response on NPEM requests.
I choose safer approach, I have no opinion.

I will follow community voice.

Thanks,
Mariusz

On Mon, 11 Mar 2024 17:30:06 -0500
Stuart Hayes <stuart.w.hayes@gmail.com> wrote:

> > > No, Linux doesn't support _DSM. It was proposed in previous
> > > iterations by Stuart but I dropped it. We decided that it need to be
> > > strongly rebuild because "pci/pcie" is not right place for ACPI code
> > > so we cannot register _DSM driver instead of NPEM as it was proposed
> > > and I don't have _DSM capable hardware to test it.  
> >  
> 
> I'm not sure I understand why pci/pcie isn't the right place for ACPI code--
> there are other _DSMs used in PCI code already, and this _DSM is defined
> in a PCI ECN.

I looked into internal review history and I found out that I dropped it after
discussion with Dan Williams:

> After review and discussion with Dan _DSM extension is dropped.

Unfortunately, I don't remember what exactly he suggested, I just remembered
conclusion that it needs to be reworked and I decided to drop it.
Maybe, I didn't understand him correctly.

Dan, could you take a look? Do you remember something?

Thanks,
Mariusz

On Tue, Mar 12, 2024 at 10:08:16AM +0100, Mariusz Tkaczyk wrote:
> On Mon, 11 Mar 2024 17:30:06 -0500
> Stuart Hayes <stuart.w.hayes@gmail.com> wrote:
> 
> > > > No, Linux doesn't support _DSM. It was proposed in previous
> > > > iterations by Stuart but I dropped it. We decided that it need to be
> > > > strongly rebuild because "pci/pcie" is not right place for ACPI code
> > > > so we cannot register _DSM driver instead of NPEM as it was proposed
> > > > and I don't have _DSM capable hardware to test it.  
> > 
> > I'm not sure I understand why pci/pcie isn't the right place for ACPI code--
> > there are other _DSMs used in PCI code already, and this _DSM is defined
> > in a PCI ECN.
> 
> I looked into internal review history and I found out that I dropped it after
> discussion with Dan Williams:
> 
> > After review and discussion with Dan _DSM extension is dropped.
> 
> Unfortunately, I don't remember what exactly he suggested, I just remembered
> conclusion that it needs to be reworked and I decided to drop it.
> Maybe, I didn't understand him correctly.
> 
> Dan, could you take a look? Do you remember something?

Straw man proposal:

  - Update this patch so we use NPEM if the device advertises it.

  - If/when Linux support for the _DSM is added, we use the _DSM when
    present.  If a device advertises NPEM but no _DSM applies to it,
    we use native NPEM for it.

Bjorn

Bjorn Helgaas wrote:
> On Tue, Mar 12, 2024 at 10:08:16AM +0100, Mariusz Tkaczyk wrote:
> > On Mon, 11 Mar 2024 17:30:06 -0500
> > Stuart Hayes <stuart.w.hayes@gmail.com> wrote:
> > 
> > > > > No, Linux doesn't support _DSM. It was proposed in previous
> > > > > iterations by Stuart but I dropped it. We decided that it need to be
> > > > > strongly rebuild because "pci/pcie" is not right place for ACPI code
> > > > > so we cannot register _DSM driver instead of NPEM as it was proposed
> > > > > and I don't have _DSM capable hardware to test it.  
> > > 
> > > I'm not sure I understand why pci/pcie isn't the right place for ACPI code--
> > > there are other _DSMs used in PCI code already, and this _DSM is defined
> > > in a PCI ECN.
> > 
> > I looked into internal review history and I found out that I dropped it after
> > discussion with Dan Williams:
> > 
> > > After review and discussion with Dan _DSM extension is dropped.
> > 
> > Unfortunately, I don't remember what exactly he suggested, I just remembered
> > conclusion that it needs to be reworked and I decided to drop it.
> > Maybe, I didn't understand him correctly.
> > 
> > Dan, could you take a look? Do you remember something?
> 
> Straw man proposal:
> 
>   - Update this patch so we use NPEM if the device advertises it.
> 
>   - If/when Linux support for the _DSM is added, we use the _DSM when
>     present.  If a device advertises NPEM but no _DSM applies to it,
>     we use native NPEM for it.

The current patch matches my last recollection of the discussion, at a
minimum do not use the NPEM interface when the _DSM is present. That was
the compromise to meet the spirit of the _DSM definition and leave it to
folks that care about the _DSM and have hardware to implement and test
that support.

However, I think the strawman is workable if only because base NPEM
already has a problem of ambiguity of which NPEM instance in a topology
should be used.

For example an NVME or CXL endpoint could have an NPEM implementation
that is superseded by an NPEM instance in its parent downstream port, or
another ancestor downstream port / root port.

The fact that the native NPEM may not be the right interface to use in
the presence of the _DSM has no specified way to resolve conflicts is at
least matched by downstream-port vs endpoint conflict resolution not
being specified.

So the spec left a bit of a mess and it is reasonable for Linux to say
"just turn on all the NPEMs and hope that userspace knows what it is
supposed to do".

On Fri, Mar 22, 2024 at 02:56:12PM -0500, Bjorn Helgaas wrote:
> Straw man proposal:
> 
>   - Update this patch so we use NPEM if the device advertises it.
> 
>   - If/when Linux support for the _DSM is added, we use the _DSM when
>     present.  If a device advertises NPEM but no _DSM applies to it,
>     we use native NPEM for it.

I've recommended to Mariusz to go the extra mile and add _DSM support
(through an npem_ops abstraction layer for register access, with _DSM
support simply consisting of an additional npem_ops declaration that
gets used if the _DSM is present).  He's currently busy implementing it.

So that forthcoming version of the series should give Stuart something
to test and hopefully settle the discussion. :)

Thanks,

Lukas