[PATCH 00/11] Add NVIDIA LSTP USB adapter drivers

[PATCH 00/11] Add NVIDIA LSTP USB adapter drivers

[Adrian Ambrozewicz]

This series adds drivers for the NVIDIA LSTP USB adapter: a USB core
driver and GPIO, LED, I2C, SPI, UART and BMC-side IPMI function drivers,
with their device tree bindings, an ACPI description document and the
sysfs ABI.

What LSTP is
------------

LSTP (Low-Speed Transport Protocol or Low-Speed Tunnelling Protocol) is
a vendor-specific USB interface (class 0xff, subclass 0x3f) that
multiplexes several low-speed "channels" over one pair of bulk
endpoints. It is implemented by NVIDIA's SMA, an MCU (0955:cf11), and
by other vendors' parts: two hub/bridge chips have it built in
(0424:4940, 174c:2214). Boards use it to
reach SPI flash, I2C sensors, GPIOs and LEDs, a UART and a host-to-BMC
IPMI path, on both BMCs and host systems.

The channel types are SPI host, I2C host, GPIO (with interrupts and LED
pins), UART, IPMI and MMIO. Channel 0 is the control channel: at probe
the driver reads the channel table from it, which gives each channel's
ID, type and configuration. The set of channels is decided by the
firmware, so the same VID:PID carries different channels on different
boards. No firmware description is needed for the channels to work.

Series layout
-------------

   1  dt-bindings: gpio: Add NVIDIA LSTP GPIO
   2  dt-bindings: i2c: Add NVIDIA LSTP I2C
   3  dt-bindings: spi: Add NVIDIA LSTP SPI
   4  dt-bindings: usb: Add NVIDIA LSTP USB adapter
   5  usb: misc: Add NVIDIA LSTP USB adapter driver
   6  gpio: Add NVIDIA LSTP GPIO driver
   7  leds: Add NVIDIA LSTP LED driver
   8  i2c: Add NVIDIA LSTP I2C driver
   9  spi: Add NVIDIA LSTP SPI driver
  10  tty: Add NVIDIA LSTP UART driver
  11  ipmi: Add NVIDIA LSTP IPMI BMC driver

Patch 4 $refs the schemas from patches 1-3, so it comes last among the
bindings; it also defines the serial@N and ipmi@N channel nodes inline.
The MAINTAINERS entry starts in patch 1 and gains each later patch's
files. Patch 5 carries:
- the core in drivers/usb/misc/;
- include/linux/usb/lstp.h for the function drivers;
- the sysfs ABI file;
- Documentation/driver-api/usb/lstp.rst;
- Documentation/firmware-guide/acpi/lstp.rst.

Patches 6 and 8-11 each depend only on patch 5; patch 7 (LEDs) also
needs patch 6, whose GPIO driver hands the LED pins to it.

Why the auxiliary bus, and why not MFD
--------------------------------------

The core binds the USB interface and owns everything shared:
- URBs and packet framing;
- request/response matching and the IRQ-style event path;
- channel 0 discovery.

Each channel the device reports is then created as an auxiliary device,
lstp.<type>.<id>, and the function drivers in their subsystems bind
those. They reach the device only through functions the core exports in
the "LSTP" symbol namespace, such as lstp_request() and lstp_send().

The closest model in tree is LJCA (drivers/usb/misc/usb-ljca.c), and
the series follows it. LJCA is a USB adapter that muxes GPIO, I2C and
SPI over its bulk endpoints. At probe it asks the device which
functions it has, creates one auxiliary device per reported function,
and exports a transfer and an event interface to the function drivers.
LSTP does the same with more channel types, with channel IDs assigned
by the device firmware, and with device tree as well as ACPI.

A channel has no registers, no MMIO and no interrupt lines of its own;
it is a logical function of one protocol stream, and its driver needs
nothing but the core's API. That is the use the auxiliary bus
documentation describes (Documentation/driver-api/auxiliary_bus.rst):
no dependency on a physical bus, device, register accesses or regmap.
It names MFD as the wrong fit for that case, because MFD relies on the
function devices being physical devices: an MFD cell is a platform
device, and its resources are ranges of the parent's memory and
interrupts (struct mfd_cell). Firmware matching does not decide between
the two, since MFD cells can also match DT nodes and ACPI _ADR children.

The same documentation says auxiliary devices "are not physical devices
that are controlled by DT/ACPI". An LSTP channel is not enumerated from
firmware either: it exists because the device reported it. Firmware
only describes it and what is attached to it. Before
auxiliary_device_add(), the core resolves each channel's node and sets
it with device_set_node():
- device tree: a child of the interface node the USB core attached;
- ACPI: a Device() under the interface's Device(), which is a child of
  the port companion (Documentation/firmware-guide/acpi/lstp.rst);
- neither: the channel has no firmware node and works as reported.
A channel matches on its address (reg, or _ADR on ACPI) plus
compatible. The I2C, SPI and GPIO cores then enumerate children and
resolve references as for any other controller.

The UART: a plain tty_driver (patch 10)
---------------------------------------

The firmware owns the UART line: baud rate, framing, parity and flow
control are provisioned on the device and only read at probe. The host
cannot read or set modem control lines; it can send a fixed-length
break, and a carrier loss reported by the device hangs the tty up unless
CLOCAL is set. Most of serial_core's uart_ops would be stubs, and
usb-serial does not fit because it binds the whole USB interface, where
the UART is one function among several. So patch 10 registers a plain
tty_driver (TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV) with one
tty_port per channel, the structure cdc-acm uses for a UART behind USB.

set_termios keeps the hardware fields at the firmware's values, so stty
reports the real line settings. The nodes are /dev/ttyLSTP<n>, parented
on the channel's auxiliary device. Jiri, Ilpo: if you would rather see
this on serial_core despite the empty uart_ops, please say so on
patch 10.

The IPMI channel: BMC side, with a message number (patch 11)
------------------------------------------------------------

On a BMC, the IPMI channel carries the host's IPMI requests to BMC
userspace and the responses back, like ssif_bmc does for SSIF; it is
not an SSIF transport and has no host-side (ipmi_si) part. Each channel
is a character device, /dev/ipmi-lstp<n>.

By default, each message on that node carries a one-byte message number
between the length and the payload, and a response must echo the number
of the request it answers. The number exists only on the node, not in
the LSTP protocol, and no other BMC-side IPMI driver has it. It names
the request a response is for: when the host has sent a newer request,
a late response to the older one is dropped, even if userspace has
already read the newer request. Without the number, a response answers
the request read last. With CONFIG_USB_LSTP_IPMI_MSG_NUM=n the node uses
ssif_bmc's struct ipmi_ssif_msg layout instead, so userspace written for
ssif_bmc works unchanged. Corey: is the message-number layout
acceptable as an LSTP-specific extension, or would you prefer it as an
option of the generic BMC message format (and ssif_bmc)?

Responses carry no tag
----------------------

The protocol has no request tag: the first response after a request is
its answer. Two places in the series depend on that:
- The core (patch 5) drops a response that arrives when no request is
  waiting, or after the waiting request already has its answer, and
  counts it in the channel's rx_late statistic. A surplus response (a
  reply to a request that timed out, one left from before a rebind, or
  a device answering twice) therefore cannot overwrite a response the
  waiter is still reading.
- The GPIO driver (patch 6) reads every pin's interrupt configuration
  at probe. A late reply can answer the next request and shift every
  later pin's state by one, so a single read is not retried on its
  own: after a timeout, all pins are read again, in alternating order,
  until two consecutive passes without a timeout agree. That is at most
  five passes, ending within 10 s of the first timeout, or the probe
  fails as it would without the re-read. The bound is there because
  the probe runs in the context that added the device, often the hub's
  worker.

The DT nodes for IPMI and UART channels
---------------------------------------

The USB binding (patch 4) defines serial@N and ipmi@N channel nodes with
only compatible, reg and status. They exist for status = "disabled",
which stops a channel the firmware reports from being created on a
board where it must not be exposed. Without a node, a channel is still
created. The binding shape, including one vendor property
(nvidia,retries on the I2C channel), is discussed in a separate mail to
the DT maintainers sent with this series:
https://lore.kernel.org/r/20261012-lstp-dt-rfc-v1-aambrozewicz@nvidia.com

What is not in this series
--------------------------

- The MMIO channel stays out of tree: raw register access, with no
  binding and no kernel consumer.
- No auto-created spidev. The out-of-tree driver has a module parameter
  that creates a spidev on every chip select of an undescribed SPI
  channel; it is not part of this series. With CONFIG_SPI_DYNAMIC,
  userspace does that through the controller's new_device attribute:

    echo "spidev <cs>" > /sys/class/spi_master/spi<B>/new_device

  (Documentation/ABI/testing/sysfs-class-spi-master)
- No separate IPMI POST-code node and no debug fault injection; both
  stay in the out-of-tree package.

Testing
-------

The drivers were tested on arm64 and x86_64 with four kinds of device:
- real endpoints, the SMA and other vendors' implementations, driven by
  the hardware test suite of the out-of-tree package on Raspberry Pi
  hosts;
- a real SMA passed through over USB to QEMU guests running
  v7.3-rc5 with this series;
- an emulated endpoint, a raw-gadget program on dummy_hcd, playing
  scripted protocol scenarios;
- the same emulator mutating its replies at random.

The test plan covers:
- every channel type end to end: SPI flash identification, write and
  read-back verification and throughput through spidev; I2C transfers;
  GPIO values, interrupts, line names and hogs; LED default states,
  brightness and hardware patterns; UART and IPMI traffic; concurrent
  traffic on all channels;
- firmware descriptions: ACPI SSDTs and device tree overlays in many
  variants, including incomplete, mismatched and outdated ones;
- lifetime: channel driver, USB interface and module unbind, rebind and
  removal, USB disconnect and reset, with nodes open and consumers
  attached, under load, and with nodes opened as soon as they appear;
- protocol faults: late, duplicate, missing and malformed replies, and
  a disconnect in the middle of a transfer;
- allocation failures injected across the interface bind and unbind,
  the function driver probes, open, read and module load.

The kernels used KASAN with kmemleak, KCSAN and KMSAN; lockdep with
PROVE_RCU, DEBUG_OBJECTS, DEBUG_LIST, DEBUG_KOBJECT_RELEASE,
DEBUG_ATOMIC_SLEEP and UBSAN; and failslab, fail_page_alloc and
fail-nth for fault injection. None of them reported a problem in these
drivers. The only reports involving them came from gpiolib when a GPIO
chip is removed with lines still requested; the fixes are posted
separately:
https://lore.kernel.org/r/20261012-gpiolib-chip-removal-v1-0-aambrozewicz@nvidia.com

Per patch, on the posted base: each patch builds (allmodconfig, W=1,
LSTP objects) on x86_64 with gcc and clang and on arm64 and arm with
gcc; sparse; kernel-doc; checkpatch --strict (clean apart from two
MACRO_ARG_REUSE checks in patch 5); dt_binding_check on each binding;
make htmldocs adds no warnings.

The out-of-tree package these drivers come from is at
https://github.com/NVIDIA/lstp_module; the version these patches match
is the public-next-v1 tag:
https://github.com/NVIDIA/lstp_module/tree/public-next-v1
It stays as the backport for kernels without this series.

Base: usb-next at bbf6b99a57b2 ("usb: typec: ucsi_ccg: Add retry
mechanism in ccg_read").

Adrian Ambrozewicz (11):
  dt-bindings: gpio: Add NVIDIA LSTP GPIO
  dt-bindings: i2c: Add NVIDIA LSTP I2C
  dt-bindings: spi: Add NVIDIA LSTP SPI
  dt-bindings: usb: Add NVIDIA LSTP USB adapter
  usb: misc: Add NVIDIA LSTP USB adapter driver
  gpio: Add NVIDIA LSTP GPIO driver
  leds: Add NVIDIA LSTP LED driver
  i2c: Add NVIDIA LSTP I2C driver
  spi: Add NVIDIA LSTP SPI driver
  tty: Add NVIDIA LSTP UART driver
  ipmi: Add NVIDIA LSTP IPMI BMC driver

 .../ABI/testing/sysfs-bus-usb-devices-lstp    |  331 ++
 .../bindings/gpio/nvidia,lstp-gpio.yaml       |  276 ++
 .../bindings/i2c/nvidia,lstp-i2c.yaml         |   71 +
 .../bindings/spi/nvidia,lstp-spi.yaml         |   68 +
 .../devicetree/bindings/usb/nvidia,lstp.yaml  |  280 ++
 Documentation/driver-api/usb/index.rst        |    1 +
 Documentation/driver-api/usb/lstp.rst         |  276 ++
 Documentation/firmware-guide/acpi/index.rst   |    1 +
 Documentation/firmware-guide/acpi/lstp.rst    |  419 +++
 MAINTAINERS                                   |   21 +
 drivers/char/ipmi/Kconfig                     |   32 +
 drivers/char/ipmi/Makefile                    |    1 +
 drivers/char/ipmi/ipmi-lstp.c                 |  464 +++
 drivers/gpio/Kconfig                          |   14 +
 drivers/gpio/Makefile                         |    1 +
 drivers/gpio/gpio-lstp.c                      | 1194 +++++++
 drivers/i2c/busses/Kconfig                    |   13 +
 drivers/i2c/busses/Makefile                   |    1 +
 drivers/i2c/busses/i2c-lstp.c                 |  573 ++++
 drivers/leds/Kconfig                          |   14 +
 drivers/leds/Makefile                         |    1 +
 drivers/leds/leds-lstp.c                      |  404 +++
 drivers/spi/Kconfig                           |   13 +
 drivers/spi/Makefile                          |    1 +
 drivers/spi/spi-lstp.c                        |  316 ++
 drivers/tty/Kconfig                           |   13 +
 drivers/tty/Makefile                          |    1 +
 drivers/tty/lstp_tty.c                        |  829 +++++
 drivers/usb/misc/Kconfig                      |   15 +
 drivers/usb/misc/Makefile                     |    1 +
 drivers/usb/misc/lstp.c                       | 2983 +++++++++++++++++
 include/linux/usb/lstp.h                      |  219 ++
 32 files changed, 8847 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-usb-devices-lstp
 create mode 100644 Documentation/devicetree/bindings/gpio/nvidia,lstp-gpio.yaml
 create mode 100644 Documentation/devicetree/bindings/i2c/nvidia,lstp-i2c.yaml
 create mode 100644 Documentation/devicetree/bindings/spi/nvidia,lstp-spi.yaml
 create mode 100644 Documentation/devicetree/bindings/usb/nvidia,lstp.yaml
 create mode 100644 Documentation/driver-api/usb/lstp.rst
 create mode 100644 Documentation/firmware-guide/acpi/lstp.rst
 create mode 100644 drivers/char/ipmi/ipmi-lstp.c
 create mode 100644 drivers/gpio/gpio-lstp.c
 create mode 100644 drivers/i2c/busses/i2c-lstp.c
 create mode 100644 drivers/leds/leds-lstp.c
 create mode 100644 drivers/spi/spi-lstp.c
 create mode 100644 drivers/tty/lstp_tty.c
 create mode 100644 drivers/usb/misc/lstp.c
 create mode 100644 include/linux/usb/lstp.h


base-commit: bbf6b99a57b2479bf51c3c8ad0946f4b8c33ed69
-- 
2.43.0

[PATCH 07/11] leds: Add NVIDIA LSTP LED driver

[Adrian Ambrozewicz]

Add a driver for the LEDs of NVIDIA LSTP USB adapters: the pins of a
GPIO channel that the firmware reports as LEDs, which the GPIO driver
offers as an auxiliary device. Each is registered with the LED class;
blink and pattern requests are handed to the adapter, which plays them
on its own. A leds child node of the channel can name the LEDs and set
their default state, trigger and pattern.

Signed-off-by: Adrian Ambrozewicz <aambrozewicz@nvidia.com>
---
 MAINTAINERS              |   1 +
 drivers/leds/Kconfig     |  14 ++
 drivers/leds/Makefile    |   1 +
 drivers/leds/leds-lstp.c | 404 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 420 insertions(+)
 create mode 100644 drivers/leds/leds-lstp.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 639cd7b6b146..c8ed59cd4b11 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -19578,6 +19578,7 @@ F:	Documentation/devicetree/bindings/usb/nvidia,lstp.yaml
 F:	Documentation/driver-api/usb/lstp.rst
 F:	Documentation/firmware-guide/acpi/lstp.rst
 F:	drivers/gpio/gpio-lstp.c
+F:	drivers/leds/leds-lstp.c
 F:	drivers/usb/misc/lstp.c
 F:	include/linux/usb/lstp.h
 
diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
index d0d3182236be..aa843e72a28d 100644
--- a/drivers/leds/Kconfig
+++ b/drivers/leds/Kconfig
@@ -1050,6 +1050,20 @@ source "drivers/leds/flash/Kconfig"
 comment "RGB LED drivers"
 source "drivers/leds/rgb/Kconfig"
 
+config LEDS_LSTP
+	tristate "LED support for NVIDIA LSTP adapters"
+	depends on LEDS_CLASS
+	depends on GPIO_LSTP
+	default GPIO_LSTP
+	help
+	  Say Y or M here to support the LEDs of NVIDIA LSTP USB adapters,
+	  the pins of the adapter's GPIO channels that the firmware reports
+	  as LEDs. They are registered with the LED class, with blink and
+	  pattern requests handed to the adapter.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called leds-lstp.
+
 comment "LED Triggers"
 source "drivers/leds/trigger/Kconfig"
 
diff --git a/drivers/leds/Makefile b/drivers/leds/Makefile
index a68244bd50fb..115b88c6b61a 100644
--- a/drivers/leds/Makefile
+++ b/drivers/leds/Makefile
@@ -60,6 +60,7 @@ obj-$(CONFIG_LEDS_LP8501)		+= leds-lp8501.o
 obj-$(CONFIG_LEDS_LP8788)		+= leds-lp8788.o
 obj-$(CONFIG_LEDS_LP8860)		+= leds-lp8860.o
 obj-$(CONFIG_LEDS_LP8864)		+= leds-lp8864.o
+obj-$(CONFIG_LEDS_LSTP)			+= leds-lstp.o
 obj-$(CONFIG_LEDS_LT3593)		+= leds-lt3593.o
 obj-$(CONFIG_LEDS_LTC3220)		+= leds-ltc3220.o
 obj-$(CONFIG_LEDS_MAX5970)		+= leds-max5970.o
diff --git a/drivers/leds/leds-lstp.c b/drivers/leds/leds-lstp.c
new file mode 100644
index 000000000000..352e484eb919
--- /dev/null
+++ b/drivers/leds/leds-lstp.c
@@ -0,0 +1,404 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * LED driver for LSTP USB interface.
+ *
+ * Copyright (c) 2026, NVIDIA CORPORATION & AFFILIATES.  All rights reserved.
+ */
+
+#include <linux/auxiliary_bus.h>
+#include <linux/build_bug.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include <linux/leds.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+
+#include <linux/usb/lstp.h>
+
+#define LSTP_LED_REPEAT_FOREVER 0 /* wire: repeats == 0 plays forever */
+#define LSTP_LED_LINUX_REPEAT_FOREVER (-1) /* LED-class pattern_set: repeat == -1 plays forever */
+#define LSTP_LED_DEFAULT_HOLD_TIME_MS 1 /* delta_t for single-step holds */
+#define LSTP_LED_DEFAULT_BLINK_MS 500 /* LED-class default when delay_on/off are both 0 */
+
+/* A GPIO channel command; the others are in gpio-lstp.c. */
+#define LSTP_GPIO_CMD_SET_LED_PATTERN 0x05
+
+struct lstp_led_pattern {
+	u8 brightness;
+	__le32 time_ms;
+} __packed;
+
+struct lstp_gpio_set_led_pattern_req {
+	__le16 pin;
+	__le32 repeats;
+	u8 num_steps;
+	struct lstp_led_pattern pattern[];
+} __packed;
+
+struct lstp_led {
+	struct led_classdev cdev;
+	struct lstp_channel *ch;
+	u16 pin;
+};
+
+/* Send SET_LED_PATTERN. @num_steps 0 clears the pattern, 1 holds forever. */
+static int lstp_led_set_pattern(struct lstp_led *led, u32 repeats,
+				const struct led_pattern *pattern, u8 num_steps)
+{
+	struct lstp_channel *ch = led->ch;
+	struct lstp_gpio_set_led_pattern_req *req;
+	size_t req_len = struct_size(req, pattern, num_steps);
+	/* The LED core applies a firmware-node max-brightness; the wire is 8-bit */
+	unsigned int max_brightness = min_t(unsigned int, led->cdev.max_brightness, U8_MAX);
+
+	/* Probe enforces bulk_tx_size >= LSTP_USB_EP_MIN_SIZE; anchor base here. */
+	BUILD_BUG_ON(sizeof(struct lstp_header) + sizeof(*req) > LSTP_USB_EP_MIN_SIZE);
+
+	for (u8 i = 0; i < num_steps; i++) {
+		if (pattern[i].brightness > max_brightness)
+			return -EINVAL;
+	}
+
+	if (req_len > ch->max_tx_payload) {
+		dev_err_ratelimited(ch->dev,
+				    "%s: ch_%d: SET_LED_PATTERN too long for led '%s' (%zu bytes, max %zu)\n",
+				    __func__, ch->ch_id, led->cdev.name, req_len,
+				    ch->max_tx_payload);
+		return -EMSGSIZE;
+	}
+
+	req = kmalloc(req_len, GFP_KERNEL);
+	if (!req)
+		return -ENOMEM;
+
+	req->pin = cpu_to_le16(led->pin);
+	req->repeats = cpu_to_le32(repeats);
+	req->num_steps = num_steps;
+	for (u8 i = 0; i < num_steps; i++) {
+		req->pattern[i].brightness = (u8)pattern[i].brightness;
+		req->pattern[i].time_ms = cpu_to_le32(pattern[i].delta_t);
+	}
+
+	int ret =
+		lstp_request(ch, LSTP_GPIO_CMD_SET_LED_PATTERN, req, req_len, NULL, 0, NULL, NULL);
+	if (ret && ret != -ENODEV)
+		dev_err_ratelimited(ch->dev,
+				    "%s: ch_%d: SET_LED_PATTERN failed for led '%s' (repeats=%u, num_steps=%u) (%pe)\n",
+				    __func__, ch->ch_id, led->cdev.name, repeats, num_steps,
+				    ERR_PTR(ret));
+
+	kfree(req);
+	return ret;
+}
+
+/*
+ * blink_set: @delay_on 0 holds OFF, @delay_off 0 holds ON, both 0 selects the
+ * LED-class 500 ms default. On-brightness is cdev->brightness, falling back to
+ * max_brightness when the LED is currently off.
+ */
+static int lstp_led_blink_set(struct led_classdev *cdev, unsigned long *delay_on,
+			      unsigned long *delay_off)
+{
+	struct lstp_led *led = container_of(cdev, struct lstp_led, cdev);
+	u8 on_value = cdev->brightness ? (u8)cdev->brightness : (u8)cdev->max_brightness;
+	struct led_pattern steps[2];
+	u8 len;
+
+	if (*delay_on == 0 && *delay_off == 0) {
+		*delay_on = LSTP_LED_DEFAULT_BLINK_MS;
+		*delay_off = LSTP_LED_DEFAULT_BLINK_MS;
+	}
+
+	if (*delay_on == 0) {
+		steps[0].delta_t = LSTP_LED_DEFAULT_HOLD_TIME_MS;
+		steps[0].brightness = LED_OFF;
+		len = 1;
+	} else if (*delay_off == 0) {
+		steps[0].delta_t = LSTP_LED_DEFAULT_HOLD_TIME_MS;
+		steps[0].brightness = on_value;
+		len = 1;
+	} else {
+		steps[0].delta_t = *delay_on;
+		steps[0].brightness = on_value;
+		steps[1].delta_t = *delay_off;
+		steps[1].brightness = LED_OFF;
+		len = 2;
+	}
+	return lstp_led_set_pattern(led, LSTP_LED_REPEAT_FOREVER, steps, len);
+}
+
+/*
+ * pattern_set: LED-class repeat -1 maps to the wire's repeats == 0 ("forever").
+ * repeat == 0 and anything below -1 are invalid.
+ */
+static int lstp_led_pattern_set(struct led_classdev *cdev, struct led_pattern *pattern, u32 len,
+				int repeat)
+{
+	struct lstp_led *led = container_of(cdev, struct lstp_led, cdev);
+
+	if (len > U8_MAX)
+		return -EMSGSIZE;
+	if (repeat == 0 || repeat < LSTP_LED_LINUX_REPEAT_FOREVER)
+		return -EINVAL;
+
+	u32 mapped_repeat = (repeat == LSTP_LED_LINUX_REPEAT_FOREVER) ? LSTP_LED_REPEAT_FOREVER :
+									(u32)repeat;
+	return lstp_led_set_pattern(led, mapped_repeat, pattern, (u8)len);
+}
+
+static int lstp_led_pattern_clear(struct led_classdev *cdev)
+{
+	struct lstp_led *led = container_of(cdev, struct lstp_led, cdev);
+
+	return lstp_led_set_pattern(led, LSTP_LED_REPEAT_FOREVER, NULL, 0);
+}
+
+/* brightness_set_blocking: a one-step pattern; @brightness is core-clamped. */
+static int lstp_led_brightness_set_blocking(struct led_classdev *cdev,
+					    enum led_brightness brightness)
+{
+	struct lstp_led *led = container_of(cdev, struct lstp_led, cdev);
+	struct led_pattern step = { .delta_t = LSTP_LED_DEFAULT_HOLD_TIME_MS,
+				    .brightness = brightness };
+
+	return lstp_led_set_pattern(led, LSTP_LED_REPEAT_FOREVER, &step, 1);
+}
+
+/*
+ * Send @fwnode's led-pattern once, repeating forever; the device then plays it
+ * without host involvement. A pattern that does not fit in one request is not
+ * sent at all.
+ */
+static void lstp_led_send_fwnode_pattern(struct lstp_led *led, struct fwnode_handle *fwnode)
+{
+	struct lstp_channel *ch = led->ch;
+	struct lstp_gpio_set_led_pattern_req *req;
+	size_t max_steps = min_t(size_t, U8_MAX,
+				 (ch->max_tx_payload - sizeof(*req)) / sizeof(req->pattern[0]));
+	int count = fwnode_property_count_u32(fwnode, "led-pattern");
+	struct led_pattern *steps = NULL;
+	unsigned int num_steps;
+	u32 *raw = NULL;
+
+	if (count <= 0 || count % 2) {
+		dev_err(ch->dev,
+			"%s: ch_%d: led-pattern of LED '%s' is not a list of <brightness duration> pairs\n",
+			__func__, ch->ch_id, led->cdev.name);
+		return;
+	}
+
+	num_steps = count / 2;
+	if (num_steps > max_steps) {
+		dev_err(ch->dev,
+			"%s: ch_%d: led-pattern of LED '%s' has %u steps, the device takes at most %zu\n",
+			__func__, ch->ch_id, led->cdev.name, num_steps, max_steps);
+		return;
+	}
+
+	raw = kcalloc(count, sizeof(*raw), GFP_KERNEL);
+	steps = kzalloc_objs(*steps, num_steps);
+	if (!raw || !steps || fwnode_property_read_u32_array(fwnode, "led-pattern", raw, count))
+		goto out;
+
+	for (unsigned int i = 0; i < num_steps; i++) {
+		if (raw[2 * i] > led->cdev.max_brightness) {
+			dev_err(ch->dev,
+				"%s: ch_%d: led-pattern of LED '%s': step %u brightness %u exceeds %u\n",
+				__func__, ch->ch_id, led->cdev.name, i, raw[2 * i],
+				led->cdev.max_brightness);
+			goto out;
+		}
+		steps[i].brightness = raw[2 * i];
+		steps[i].delta_t = raw[2 * i + 1];
+	}
+
+	lstp_led_set_pattern(led, LSTP_LED_REPEAT_FOREVER, steps, num_steps);
+out:
+	kfree(steps);
+	kfree(raw);
+}
+
+/*
+ * default-state is written once, and a missing one means "off". "keep" leaves
+ * the LED as the device firmware set it: the device cannot report its current
+ * state, so there is nothing to read back.
+ */
+static void lstp_led_apply_default_state(struct lstp_led *led, struct fwnode_handle *fwnode)
+{
+	switch (led_init_default_state_get(fwnode)) {
+	case LEDS_DEFSTATE_KEEP:
+		return;
+	case LEDS_DEFSTATE_ON:
+		led->cdev.brightness = led->cdev.max_brightness;
+		break;
+	default:
+		led->cdev.brightness = LED_OFF;
+		break;
+	}
+
+	lstp_led_brightness_set_blocking(&led->cdev, led->cdev.brightness);
+}
+
+static void lstp_led_put_fwnode(void *fwnode)
+{
+	fwnode_handle_put(fwnode);
+}
+
+/*
+ * led_classdev_unregister() flushes set_brightness_work before it removes the
+ * sysfs files, and the LED core does not refuse brightness or trigger writes in
+ * between: such a write would queue work or attach a trigger that outlives
+ * @data. Disable sysfs first, under led_access, so they fail with -EBUSY.
+ */
+static void lstp_led_unregister(void *data)
+{
+	struct led_classdev *cdev = data;
+
+	mutex_lock(&cdev->led_access);
+	led_sysfs_disable(cdev);
+	mutex_unlock(&cdev->led_access);
+	led_classdev_unregister(cdev);
+}
+
+static int lstp_led_classdev_register(struct device *dev, struct led_classdev *cdev,
+				      struct led_init_data *init_data)
+{
+	int ret = led_classdev_register_ext(dev, cdev, init_data);
+
+	if (ret)
+		return ret;
+	return devm_add_action_or_reset(dev, lstp_led_unregister, cdev);
+}
+
+/* Register @led, initialised from @fwnode if any. A failure leaves the other LEDs up. */
+static int lstp_led_register(struct device *dev, struct lstp_led *led, struct fwnode_handle *fwnode)
+{
+	int ret;
+
+	if (!fwnode) {
+		ret = lstp_led_classdev_register(dev, &led->cdev, NULL);
+	} else {
+		struct led_init_data init_data = { .fwnode = fwnode };
+
+		/*
+		 * The class device keeps @fwnode as its node, and default_trigger
+		 * points into it. Queued first, the put runs after unregistration.
+		 */
+		ret = devm_add_action_or_reset(dev, lstp_led_put_fwnode, fwnode_handle_get(fwnode));
+		if (!ret) {
+			bool pattern = fwnode_property_present(fwnode, "led-pattern");
+			bool trigger = fwnode_property_present(fwnode, "linux,default-trigger");
+
+			/* A trigger takes precedence; the LED core applies it from @fwnode. */
+			if (pattern && trigger)
+				dev_err(dev,
+					"%s: ch_%d: Ignoring led-pattern of LED '%s': %pfw also sets linux,default-trigger\n",
+					__func__, led->ch->ch_id, led->cdev.name, fwnode);
+			if (pattern && !trigger)
+				lstp_led_send_fwnode_pattern(led, fwnode);
+			else
+				lstp_led_apply_default_state(led, fwnode);
+			ret = lstp_led_classdev_register(dev, &led->cdev, &init_data);
+		}
+	}
+
+	if (ret)
+		dev_warn(dev, "%s: ch_%d: Could not register LED '%s', pin %u (%pe)\n", __func__,
+			 led->ch->ch_id, led->cdev.name, led->pin, ERR_PTR(ret));
+	return ret;
+}
+
+static struct lstp_led *lstp_led_by_pin(struct lstp_led *leds, u16 nleds, u32 pin)
+{
+	for (u16 i = 0; i < nleds; i++) {
+		if (leds[i].pin == pin)
+			return &leds[i];
+	}
+	return NULL;
+}
+
+/*
+ * Register the LEDs described under the channel's "leds" node, then every other
+ * LED pin under its firmware pin name. A node that does not describe a
+ * firmware-reported LED pin, or that names no LED, is ignored.
+ */
+static int lstp_leds_probe(struct auxiliary_device *auxdev, const struct auxiliary_device_id *id)
+{
+	struct lstp_leds *pins = container_of(auxdev, struct lstp_leds, auxdev);
+	struct lstp_channel *ch = pins->ch;
+	struct device *dev = &auxdev->dev;
+	struct fwnode_handle *node;
+	struct fwnode_handle *child;
+	struct lstp_led *leds;
+
+	leds = devm_kcalloc(dev, pins->npins, sizeof(*leds), GFP_KERNEL);
+	if (!leds)
+		return -ENOMEM;
+
+	for (u16 i = 0; i < pins->npins; i++) {
+		leds[i].ch = ch;
+		leds[i].pin = pins->pins[i].pin;
+		leds[i].cdev.name = pins->pins[i].name;
+		leds[i].cdev.max_brightness = U8_MAX;
+		leds[i].cdev.flags = LED_HW_PLUGGABLE;
+		leds[i].cdev.brightness_set_blocking = lstp_led_brightness_set_blocking;
+		leds[i].cdev.blink_set = lstp_led_blink_set;
+		leds[i].cdev.pattern_set = lstp_led_pattern_set;
+		leds[i].cdev.pattern_clear = lstp_led_pattern_clear;
+	}
+
+	node = fwnode_get_named_child_node(ch->fwnode, "leds");
+	/*
+	 * Not the available-child iterator; see Documentation/driver-api/usb/lstp.rst.
+	 * On OF, fwnode_for_each_child_node() already skips disabled nodes.
+	 */
+	fwnode_for_each_child_node(node, child) {
+		struct lstp_led *led = NULL;
+		u32 pin;
+
+		if (!fwnode_property_read_u32(child, "reg", &pin))
+			led = lstp_led_by_pin(leds, pins->npins, pin);
+		if (!led) {
+			dev_warn(dev, "%s: ch_%d: Ignoring %pfw: not an LED pin\n", __func__,
+				 ch->ch_id, child);
+			continue;
+		}
+		if (led->cdev.dev) {
+			dev_warn(dev, "%s: ch_%d: Ignoring %pfw: pin %u is already described\n",
+				 __func__, ch->ch_id, child, pin);
+			continue;
+		}
+		if (!fwnode_property_present(child, "label") &&
+		    !fwnode_property_present(child, "function")) {
+			dev_warn(dev, "%s: ch_%d: Ignoring %pfw: neither label nor function\n",
+				 __func__, ch->ch_id, child);
+			continue;
+		}
+		lstp_led_register(dev, led, child);
+	}
+	fwnode_handle_put(node);
+
+	for (u16 i = 0; i < pins->npins; i++) {
+		if (!leds[i].cdev.dev)
+			lstp_led_register(dev, &leds[i], NULL);
+	}
+
+	return 0;
+}
+
+static const struct auxiliary_device_id lstp_leds_id_table[] = { { .name = "lstp.led" }, {} };
+MODULE_DEVICE_TABLE(auxiliary, lstp_leds_id_table);
+
+static struct auxiliary_driver lstp_leds_drv = {
+	.name = "led",
+	.probe = lstp_leds_probe,
+	.id_table = lstp_leds_id_table,
+};
+module_auxiliary_driver(lstp_leds_drv);
+
+MODULE_IMPORT_NS("LSTP");
+MODULE_DESCRIPTION("LSTP LED driver");
+MODULE_LICENSE("GPL");
-- 
2.43.0

Re: [PATCH 07/11] leds: Add NVIDIA LSTP LED driver

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
- [High] leds: applying initial brightness before parsing DT max-brightness
- [Medium] leds: rejecting DT nodes with only color and allowing deprecated label
- [Low] leds: non-standard commit message prefix missing driver name
--

commit 231bdc9e871148317f849221691f708a54dbd399
Author: Adrian Ambrozewicz <aambrozewicz@nvidia.com>

leds: Add NVIDIA LSTP LED driver
    
This commit introduces a new driver for LEDs on NVIDIA LSTP USB adapters.
It uses the GPIO channel of the adapter, hands blink and pattern requests
directly to the hardware, and configures them via device tree child nodes.

> leds: Add NVIDIA LSTP LED driver

[Severity: Low]
This isn't a bug, but the commit message prefix seems to be missing the
driver name. Should this follow the standard format, such as
"leds: lstp: Add NVIDIA LSTP LED driver" to help with git history
categorization?

diff --git a/drivers/leds/leds-lstp.c b/drivers/leds/leds-lstp.c
new file mode 100644
index 0000000000000..352e484eb9194
--- /dev/null
+++ b/drivers/leds/leds-lstp.c
[ ... ]
@@ -275,20 +275,21 @@ static int lstp_led_register(struct device *dev, struct lstp_led *led, struct fw
+		if (!ret) {
+			bool pattern = fwnode_property_present(fwnode, "led-pattern");
+			bool trigger = fwnode_property_present(fwnode, "linux,default-trigger");
+
+			/* A trigger takes precedence; the LED core applies it from @fwnode. */
+			if (pattern && trigger)
+				dev_err(dev,
+					"%s: ch_%d: Ignoring led-pattern of LED '%s': %pfw also sets linux,default-trigger\n",
+					__func__, led->ch->ch_id, led->cdev.name, fwnode);
+			if (pattern && !trigger)
+				lstp_led_send_fwnode_pattern(led, fwnode);
+			else
+				lstp_led_apply_default_state(led, fwnode);

[Severity: High]
Does applying the initial hardware state here happen too early? At this
point, led_classdev_register_ext() has not yet been called, so the device
tree max-brightness property hasn't been parsed into led->cdev.max_brightness.

As a result, lstp_led_apply_default_state() will use the uninitialized
max_brightness value of 255 (U8_MAX) to drive the hardware. Could this risk
over-driving the hardware before the registration layer correctly enforces
the bound?

+			ret = lstp_led_classdev_register(dev, &led->cdev, &init_data);
+		}
+	}
+
+	if (ret)
+		dev_warn(dev, "%s: ch_%d: Could not register LED '%s', pin %u (%pe)\n", __func__,
+			 led->ch->ch_id, led->cdev.name, led->pin, ERR_PTR(ret));
+	return ret;
+}
[ ... ]
@@ -328,34 +328,41 @@ static int lstp_leds_probe(struct auxiliary_device *auxdev, const struct auxilia
[ ... ]
+		if (led->cdev.dev) {
+			dev_warn(dev, "%s: ch_%d: Ignoring %pfw: pin %u is already described\n",
+				 __func__, ch->ch_id, child, pin);
+			continue;
+		}
+		if (!fwnode_property_present(child, "label") &&
+		    !fwnode_property_present(child, "function")) {

[Severity: Medium]
Does this logic incorrectly reject modern device tree nodes? The LED
subsystem guidelines dictate that the label property is deprecated and
should be avoided, while color and function are preferred.

By warning and skipping nodes that lack both label and function, valid
modern DT nodes that rely solely on the color property (e.g.,
color = <LED_COLOR_ID_GREEN>) would be entirely rejected. Should this check
be updated to account for the color property and align with modern naming
requirements?

+			dev_warn(dev, "%s: ch_%d: Ignoring %pfw: neither label nor function\n",
+				 __func__, ch->ch_id, child);
+			continue;
+		}
+		lstp_led_register(dev, led, child);
+	}
+	fwnode_handle_put(node);
+
+	for (u16 i = 0; i < pins->npins; i++) {
+		if (!leds[i].cdev.dev)
+			lstp_led_register(dev, &leds[i], NULL);
+	}
+
+	return 0;
+}
[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261012-lstp-usb-adapter-v1-0-aambrozewicz@nvidia.com?part=7

Re: [PATCH 00/11] Add NVIDIA LSTP USB adapter drivers

[Greg Kroah-Hartman]

On Mon, Oct 12, 2026 at 08:35:58PM +0300, Adrian Ambrozewicz wrote:
> This series adds drivers for the NVIDIA LSTP USB adapter: a USB core
> driver and GPIO, LED, I2C, SPI, UART and BMC-side IPMI function drivers,
> with their device tree bindings, an ACPI description document and the
> sysfs ABI.

Why would a USB device have anything to do with device tree?

> What LSTP is
> ------------
> 
> LSTP (Low-Speed Transport Protocol or Low-Speed Tunnelling Protocol) is
> a vendor-specific USB interface (class 0xff, subclass 0x3f) that
> multiplexes several low-speed "channels" over one pair of bulk
> endpoints. It is implemented by NVIDIA's SMA, an MCU (0955:cf11), and
> by other vendors' parts: two hub/bridge chips have it built in
> (0424:4940, 174c:2214). Boards use it to
> reach SPI flash, I2C sensors, GPIOs and LEDs, a UART and a host-to-BMC
> IPMI path, on both BMCs and host systems.

Cute, but that's a total abuse of the USB standard.  Why wasn't this
implemented by the proper "each channel is a USB interface" model
instead?  Have the firmware engineers there not read the USB spec?

> The channel types are SPI host, I2C host, GPIO (with interrupts and LED
> pins), UART, IPMI and MMIO. Channel 0 is the control channel: at probe
> the driver reads the channel table from it, which gives each channel's
> ID, type and configuration. The set of channels is decided by the
> firmware, so the same VID:PID carries different channels on different
> boards. No firmware description is needed for the channels to work.

Again cute, but that's not how USB devices are supposed to work, why
would we want to do this at all?

> Series layout
> -------------
> 
>    1  dt-bindings: gpio: Add NVIDIA LSTP GPIO
>    2  dt-bindings: i2c: Add NVIDIA LSTP I2C
>    3  dt-bindings: spi: Add NVIDIA LSTP SPI
>    4  dt-bindings: usb: Add NVIDIA LSTP USB adapter

USB devices do not have DT bindings.  It's a dynamic bus, with
self-describing devices, don't make the mistake of thinking this is
giong to work.

>    5  usb: misc: Add NVIDIA LSTP USB adapter driver
>    6  gpio: Add NVIDIA LSTP GPIO driver
>    7  leds: Add NVIDIA LSTP LED driver
>    8  i2c: Add NVIDIA LSTP I2C driver
>    9  spi: Add NVIDIA LSTP SPI driver
>   10  tty: Add NVIDIA LSTP UART driver
>   11  ipmi: Add NVIDIA LSTP IPMI BMC driver

So you have a custom "bus" for a single USB device/interface?  Ick,
again, why?  Please do this the "proper" way in your firmware and do
this one-device-per-usb-interface like the rest of the world does
please.

Doing it that way will not cost any more hardware pins at all, it's all
handled in firmware, and as you all have complete control over the
firmware, you can fix this up now to do things properly.

> Patch 4 $refs the schemas from patches 1-3, so it comes last among the
> bindings; it also defines the serial@N and ipmi@N channel nodes inline.
> The MAINTAINERS entry starts in patch 1 and gains each later patch's
> files. Patch 5 carries:
> - the core in drivers/usb/misc/;
> - include/linux/usb/lstp.h for the function drivers;
> - the sysfs ABI file;
> - Documentation/driver-api/usb/lstp.rst;
> - Documentation/firmware-guide/acpi/lstp.rst.
> 
> Patches 6 and 8-11 each depend only on patch 5; patch 7 (LEDs) also
> needs patch 6, whose GPIO driver hands the LED pins to it.
> 
> Why the auxiliary bus, and why not MFD
> --------------------------------------

Neither is ok for USB devices, that's not an argument either way.

Please go talk to some people with USB spec experience on how to make a
multi-function device correctly.  This way sure does not look like it at
all.

thanks,

greg k-h

Re: [PATCH 00/11] Add NVIDIA LSTP USB adapter drivers

[Greg Kroah-Hartman]

On Mon, Oct 12, 2026 at 08:35:58PM +0300, Adrian Ambrozewicz wrote:
> This series adds drivers for the NVIDIA LSTP USB adapter: a USB core
> driver and GPIO, LED, I2C, SPI, UART and BMC-side IPMI function drivers,
> with their device tree bindings, an ACPI description document and the
> sysfs ABI.
> 
> What LSTP is
> ------------
> 
> LSTP (Low-Speed Transport Protocol or Low-Speed Tunnelling Protocol) is
> a vendor-specific USB interface (class 0xff, subclass 0x3f) that
> multiplexes several low-speed "channels" over one pair of bulk
> endpoints. It is implemented by NVIDIA's SMA, an MCU (0955:cf11), and
> by other vendors' parts: two hub/bridge chips have it built in
> (0424:4940, 174c:2214). Boards use it to
> reach SPI flash, I2C sensors, GPIOs and LEDs, a UART and a host-to-BMC
> IPMI path, on both BMCs and host systems.

Also, if you really want to do this in a dynamic way, use greybus, as
that is EXPLICITLY what it was designed for, and is patent-free (i.e.
unencumbered, and we already support it in the kernel.)  Please don't
reinvent the wheel/spec just because no one did any prior-art
research...

thanks,

greg k-h