diff --git a/Documentation/ABI/testing/sysfs-class-spi-master b/Documentation/ABI/testing/sysfs-class-spi-master new file mode 100644 index 000000000000..0a524fcd96d2 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-spi-master @@ -0,0 +1,34 @@ +What: /sys/class/spi_master/spiB/new_device +Date: July 2026 +KernelVersion: 7.3 +Contact: linux-spi@vger.kernel.org +Description: (WO) Instantiate a new SPI device on bus B, where B + is the bus number (0, 1, 2, ...). Takes parameters + in the format: + + [ []] + + where modalias is the driver name, chip_select is the + CS line number, and max_speed_hz and mode are optional. + + The device can later be removed with delete_device. + + Only devices created via this interface can be removed + with delete_device; platform and DT devices are not + affected. + + Example: + # echo spidev 0 > /sys/class/spi_master/spi0/new_device + # echo spidev 0 10000000 > /sys/class/spi_master/spi0/new_device + # echo spidev 0 10000000 3 > /sys/class/spi_master/spi0/new_device + +What: /sys/class/spi_master/spiB/delete_device +Date: July 2026 +KernelVersion: 7.3 +Contact: linux-spi@vger.kernel.org +Description: (WO) Remove a SPI device previously created via + new_device. Takes a single parameter: the chip select + number of the device to remove. + + Example: + # echo 0 > /sys/class/spi_master/spi0/delete_device diff --git a/Documentation/spi/index.rst b/Documentation/spi/index.rst index ac0c2233ce48..3f723e2c07da 100644 --- a/Documentation/spi/index.rst +++ b/Documentation/spi/index.rst @@ -8,6 +8,7 @@ Serial Peripheral Interface (SPI) :maxdepth: 1 spi-summary + instantiating-devices spidev multiple-data-lanes butterfly diff --git a/Documentation/spi/instantiating-devices.rst b/Documentation/spi/instantiating-devices.rst new file mode 100644 index 000000000000..ec07353b425d --- /dev/null +++ b/Documentation/spi/instantiating-devices.rst @@ -0,0 +1,88 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================== +How to instantiate SPI devices +============================== + +SPI devices are normally declared statically via device-tree, ACPI, or +board files. When the SPI controller is registered, these devices are +instantiated automatically by the SPI core. This is the preferred method +for any device with a proper kernel driver. + +Instantiate from user-space +--------------------------- + +In certain cases a SPI device cannot be declared statically: + +* The ``spidev`` driver, which provides raw userspace access to SPI + buses, explicitly rejects the bare ``"spidev"`` compatible string in + device-tree because spidev is a Linux implementation detail, not a + hardware description. Vendor-specific compatible strings for spidev + (e.g. ``"vendor,board-spidev"``) are also generally not accepted + upstream. Device-tree overlays do not help here either, since the + spidev driver performs the same compatible check regardless of how + the DT node was loaded. + +* You are developing or testing a SPI device on a development board + where the SPI bus is exposed on expansion headers, and the connected + device may change frequently. + +For these cases, a sysfs interface is provided on each SPI host controller +(similar to the I2C ``new_device``/``delete_device`` interface described +in Documentation/i2c/instantiating-devices.rst). Two write-only +attribute files are created in every SPI host controller directory: +``new_device`` and ``delete_device``. + +File ``new_device`` takes 2 to 4 parameters: the name of the SPI +device (a string), the chip select number, and optionally +``max_speed_hz`` and ``mode``:: + + [ []] + +The modalias is set both as the device's ``modalias`` field and as its +``driver_override``. This ensures that the device binds to the named +driver directly, bypassing the normal bus matching logic (OF, ACPI, +and ``id_table``). This is necessary because drivers like ``spidev`` +deliberately exclude generic names from their ``id_table``. + +If ``max_speed_hz`` is omitted or 0, ``spi_setup()`` clamps it to +the controller's maximum speed. If ``mode`` is omitted, SPI mode 0 +(CPOL=0, CPHA=0) is used. + +File ``delete_device`` takes a single parameter: the chip select +number. As no two devices can share a chip select on a given SPI bus, +the chip select is sufficient to uniquely identify the device. + +Examples:: + + # Create a spidev device on SPI bus 0, chip select 0 + echo spidev 0 > /sys/class/spi_master/spi0/new_device + + # Create with explicit clock rate and SPI mode + echo spidev 0 10000000 3 > /sys/class/spi_master/spi0/new_device + + # Remove the device + echo 0 > /sys/class/spi_master/spi0/delete_device + +The attributes are added after the host controller and its firmware-described +devices have been registered. Their addition emits a ``change`` uevent, +allowing a udev rule to write to ``new_device`` when the interface is ready. + +Limitations +^^^^^^^^^^^ + +Devices created through this interface have the following limitations +compared to devices declared via device-tree: + +* No interrupt (IRQ) support. +* No additional properties such as ``spi-max-frequency`` DT bindings + or controller-specific configuration. +* No platform data or software nodes. + +For ``spidev`` usage these limitations are not relevant, since spidev +provides a raw byte-level interface that does not require any of these +features. + +Only devices created via ``new_device`` can be removed through +``delete_device``. Devices declared via device-tree, ACPI, or board +files are not affected by this interface. diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c index d9e6b4b87c89..07c572e1df5d 100644 --- a/drivers/spi/spi.c +++ b/drivers/spi/spi.c @@ -43,6 +43,7 @@ EXPORT_TRACEPOINT_SYMBOL(spi_transfer_stop); #include "internals.h" static int __spi_setup(struct spi_device *spi, bool initial_setup); +static int __spi_add_device(struct spi_device *spi, struct spi_device *parent); static DEFINE_IDR(spi_controller_idr); @@ -297,6 +298,192 @@ static const struct attribute_group spi_controller_statistics_group = { .attrs = spi_controller_statistics_attrs, }; +#if IS_ENABLED(CONFIG_SPI_DYNAMIC) + +/* + * new_device_store - instantiate a new SPI device from userspace + * + * Takes parameters: [ []] + * + * Examples: + * echo spidev 0 > new_device + * echo spidev 0 10000000 > new_device + * echo spidev 0 10000000 3 > new_device + */ +static ssize_t +new_device_store(struct device *dev, struct device_attribute *attr, + const char *buf, size_t count) +{ + struct spi_controller *ctlr = container_of(dev, struct spi_controller, + dev); + struct spi_device *spi; + char modalias[SPI_NAME_SIZE]; + unsigned int chip_select; + u32 max_speed_hz = 0; + u32 mode = 0; + char *blank; + int status; + + blank = strchr(buf, ' '); + if (!blank) { + dev_err(dev, "new_device: Missing parameters\n"); + return -EINVAL; + } + + if (blank == buf || blank - buf > SPI_NAME_SIZE - 1) { + dev_err(dev, "new_device: Invalid device name\n"); + return -EINVAL; + } + + memset(modalias, 0, sizeof(modalias)); + memcpy(modalias, buf, blank - buf); + + /* + * sscanf fills only the fields it matches; unmatched optional + * fields (max_speed_hz, mode) stay zero from initialisation above. + * max_speed_hz == 0 is clamped to the controller max by spi_setup(). + * mode == 0 selects SPI mode 0 (CPOL=0, CPHA=0). + */ + if (sscanf(++blank, "%u %u %u", &chip_select, &max_speed_hz, &mode) < 1) { + dev_err(dev, "new_device: Can't parse chip select\n"); + return -EINVAL; + } + + /* + * spi_device.chip_select[] is u8, so cap at U8_MAX independently of + * ctlr->num_chipselect (which is u16 and may exceed 255). Without + * this, values in (U8_MAX, num_chipselect) would silently truncate + * inside spi_set_chipselect() and select the wrong CS. + */ + if (chip_select > U8_MAX || chip_select >= ctlr->num_chipselect) { + dev_err(dev, "new_device: Chip select %u out of range (num_chipselect=%u)\n", + chip_select, ctlr->num_chipselect); + return -EINVAL; + } + + /* + * Reject kernel-internal mode bits (SPI_NO_TX, SPI_NO_RX, + * SPI_TPM_HW_FLOW, ...). These are set only by in-kernel drivers + * that know they are safe on their controller/device pair and must + * not be settable through a userspace-writable sysfs. Matches + * spidev's SPI_IOC_WR_MODE32 handling (drivers/spi/spidev.c). + */ + if (mode & ~(u32)SPI_MODE_USER_MASK) { + dev_err(dev, "new_device: Invalid mode bits 0x%x\n", + mode & ~(u32)SPI_MODE_USER_MASK); + return -EINVAL; + } + + spi = spi_alloc_device(ctlr); + if (!spi) + return -ENOMEM; + + spi_set_chipselect(spi, 0, chip_select); + spi->max_speed_hz = max_speed_hz; + spi->mode = mode; + spi->cs_index_mask = BIT(0); + strscpy(spi->modalias, modalias, sizeof(spi->modalias)); + + /* + * Set driver_override so that the device binds to the driver + * named by modalias regardless of whether that driver's + * id_table contains a matching entry. This is needed because + * some drivers (e.g. spidev) deliberately omit generic names + * from their id_table. + */ + status = device_set_driver_override(&spi->dev, modalias); + if (status) { + spi_dev_put(spi); + return status; + } + + /* + * spi_unregister_controller() removes the new_device/delete_device + * sysfs group before taking add_lock, so kernfs_drain() has already + * completed by the time we get here and we cannot be racing with + * teardown. Take add_lock to serialise the __spi_add_device() and + * list insertion with respect to non-sysfs callers of + * __spi_add_device() (DT/ACPI, ancillary), which check + * device_is_registered(&ctlr->dev) under the same lock. + */ + mutex_lock(&ctlr->add_lock); + + status = __spi_add_device(spi, NULL); + if (status) { + mutex_unlock(&ctlr->add_lock); + spi_dev_put(spi); + return status; + } + + list_add_tail(&spi->userspace_node, &ctlr->userspace_clients); + mutex_unlock(&ctlr->add_lock); + + dev_info(dev, "new_device: Instantiated device %s at CS%u\n", + modalias, chip_select); + return count; +} +static DEVICE_ATTR_IGNORE_LOCKDEP(new_device, 0200, NULL, new_device_store); + +static ssize_t +delete_device_store(struct device *dev, struct device_attribute *attr, + const char *buf, size_t count) +{ + struct spi_controller *ctlr = container_of(dev, struct spi_controller, + dev); + struct spi_device *spi, *next; + unsigned short cs; + char end; + int res; + + res = sscanf(buf, "%hu%c", &cs, &end); + if (res < 1) { + dev_err(dev, "delete_device: Can't parse chip select\n"); + return -EINVAL; + } + if (res > 1 && end != '\n') { + dev_err(dev, "delete_device: Unexpected parameters\n"); + return -EINVAL; + } + + res = -ENOENT; + mutex_lock(&ctlr->add_lock); + list_for_each_entry_safe(spi, next, &ctlr->userspace_clients, + userspace_node) { + if (spi_get_chipselect(spi, 0) == cs) { + dev_info(dev, "delete_device: Deleting device %s at CS%u\n", + spi->modalias, cs); + list_del(&spi->userspace_node); + spi_unregister_device(spi); + res = count; + break; + } + } + mutex_unlock(&ctlr->add_lock); + + if (res < 0) + dev_err(dev, "delete_device: Can't find device in list\n"); + return res; +} +static DEVICE_ATTR_IGNORE_LOCKDEP(delete_device, 0200, NULL, + delete_device_store); + +static struct attribute *spi_controller_userspace_attrs[] = { + &dev_attr_new_device.attr, + &dev_attr_delete_device.attr, + NULL, +}; + +static const struct attribute_group spi_controller_userspace_group = { + .attrs = spi_controller_userspace_attrs, +}; + +#endif /* CONFIG_SPI_DYNAMIC */ + +/* + * spi_controller_userspace_group is registered manually for host controllers + * at the end of spi_register_controller() so new_device/delete_device only + * appear after DT/ACPI children and the queue are set up. + */ static const struct attribute_group *spi_controller_groups[] = { &spi_controller_statistics_group, NULL, @@ -3259,6 +3446,9 @@ struct spi_controller *__spi_alloc_controller(struct device *dev, mutex_init(&ctlr->bus_lock_mutex); mutex_init(&ctlr->io_mutex); mutex_init(&ctlr->add_lock); +#if IS_ENABLED(CONFIG_SPI_DYNAMIC) + INIT_LIST_HEAD(&ctlr->userspace_clients); +#endif ctlr->bus_num = -1; ctlr->num_chipselect = 1; ctlr->num_data_lanes = 1; @@ -3552,6 +3742,29 @@ int spi_register_controller(struct spi_controller *ctlr) of_register_spi_devices(ctlr); acpi_register_spi_devices(ctlr); +#if IS_ENABLED(CONFIG_SPI_DYNAMIC) + /* + * Register the new_device/delete_device sysfs interface as the + * final step of host controller bringup, only after the queue, + * boardinfo matching and DT/ACPI enumeration have all completed. + * If this fails, the controller is otherwise usable, so log and + * carry on rather than tearing everything down. + */ + if (!spi_controller_is_target(ctlr)) { + status = sysfs_create_group(&ctlr->dev.kobj, + &spi_controller_userspace_group); + if (status) { + dev_warn(&ctlr->dev, + "Failed to create userspace client interface: %d\n", + status); + } else { + ctlr->userspace_registered = true; + /* Notify userspace that the new attributes are available. */ + kobject_uevent(&ctlr->dev.kobj, KOBJ_CHANGE); + } + } +#endif + return 0; del_ctrl: @@ -3616,10 +3829,43 @@ void spi_unregister_controller(struct spi_controller *ctlr) struct spi_controller *found; int id = ctlr->bus_num; + /* + * Drain in-flight new_device/delete_device sysfs stores and + * prevent new ones from starting. Must happen before we take + * add_lock so kernfs_drain doesn't wait on a store that is + * itself blocked on add_lock. + */ +#if IS_ENABLED(CONFIG_SPI_DYNAMIC) + if (ctlr->userspace_registered) { + sysfs_remove_group(&ctlr->dev.kobj, + &spi_controller_userspace_group); + ctlr->userspace_registered = false; + } +#endif + /* Prevent addition of new devices, unregister existing ones */ if (IS_ENABLED(CONFIG_SPI_DYNAMIC)) mutex_lock(&ctlr->add_lock); +#if IS_ENABLED(CONFIG_SPI_DYNAMIC) + /* + * Drain userspace_clients before __unregister since + * spi_unregister_device() doesn't do list_del() itself. The + * userspace sysfs group has already been removed above and + * kernfs_drain() has completed, so no new entries can appear + * here. + */ + while (!list_empty(&ctlr->userspace_clients)) { + struct spi_device *spi; + + spi = list_first_entry(&ctlr->userspace_clients, + struct spi_device, + userspace_node); + list_del(&spi->userspace_node); + spi_unregister_device(spi); + } +#endif + device_for_each_child(&ctlr->dev, NULL, __unregister); /* First make sure that this controller was ever added */ diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h index 4c285d3ede1d..88d17fce02dc 100644 --- a/include/linux/spi/spi.h +++ b/include/linux/spi/spi.h @@ -179,6 +179,8 @@ extern void spi_transfer_cs_change_delay_exec(struct spi_message *msg, * @num_tx_lanes: Number of transmit lanes wired up. * @rx_lane_map: Map of peripheral lanes (index) to controller lanes (value). * @num_rx_lanes: Number of receive lanes wired up. + * @userspace_node: entry on the parent controller's userspace_clients list + * when this device was instantiated via the sysfs new_device interface * * A @spi_device is used to interchange data between an SPI target device * (usually a discrete chip) and CPU memory. @@ -252,6 +254,10 @@ struct spi_device { u8 rx_lane_map[SPI_DEVICE_DATA_LANE_CNT_MAX]; u8 num_rx_lanes; +#if IS_ENABLED(CONFIG_SPI_DYNAMIC) + struct list_head userspace_node; +#endif + /* * Likely need more hooks for more protocol options affecting how * the controller talks to each chip, like: @@ -555,6 +561,11 @@ extern struct spi_device *devm_spi_new_ancillary_device(struct spi_device *spi, * @defer_optimize_message: set to true if controller cannot pre-optimize messages * and needs to defer the optimization step until the message is actually * being transferred + * @userspace_clients: list of SPI devices instantiated from userspace via + * the sysfs new_device interface; protected by @add_lock + * @userspace_registered: true once the new_device/delete_device sysfs + * group has been added by spi_register_controller(); used by + * spi_unregister_controller() to know whether to remove it * * Each SPI controller can communicate with one or more @spi_device * children. These make a small bus, sharing MOSI, MISO and SCK signals @@ -807,6 +818,13 @@ struct spi_controller { bool queue_empty; bool must_async; bool defer_optimize_message; + +#if IS_ENABLED(CONFIG_SPI_DYNAMIC) + /* List of userspace-instantiated devices; protected by @add_lock */ + struct list_head userspace_clients; + /* True after new_device/delete_device sysfs group is created */ + bool userspace_registered; +#endif }; static inline void *spi_controller_get_devdata(struct spi_controller *ctlr)