From 9b1847a340ef73ac10f123393705d34404fa2c4e Mon Sep 17 00:00:00 2001 From: Vishwaroop A Date: Mon, 3 Aug 2026 10:46:13 +0000 Subject: spi: add new_device/delete_device sysfs interface Development boards such as the Jetson AGX Orin expose SPI buses on expansion headers (e.g. the 40-pin header) so that users can connect and interact with SPI peripherals from userspace. The standard way to get /dev/spidevB.C character device nodes for this purpose is to register spi_device instances backed by the spidev driver. Today there is no viable way to do this on upstream kernels: - The spidev driver rejects the bare "spidev" compatible string in DT, since spidev is a Linux software interface and not a description of real hardware. - Vendor-specific compatible strings (e.g. "nvidia,tegra-spidev") have been rejected by DT maintainers for the same reason. The I2C subsystem solved an analogous problem by exposing new_device/delete_device sysfs attributes on each adapter. Add the same interface to SPI host controllers, so that userspace (e.g. a systemd unit at boot) can instantiate SPI devices at runtime without needing anything in device-tree. The new_device file accepts: [ []] where chip_select is required, while max_speed_hz and mode are optional and default to 0 if omitted. max_speed_hz == 0 is clamped to the controller's maximum by spi_setup(); mode == 0 selects SPI mode 0 (CPOL=0, CPHA=0). The modalias is used both as the device identifier and as a driver_override, so that the device binds to the named driver directly. This is necessary because some drivers like spidev deliberately exclude generic names from their id_table. Devices created this way are limited compared to those declared via DT or board files: - No IRQ is assigned (the device gets IRQ 0 / no interrupt). - No platform_data or device properties are attached. - No OF node is associated with the device. These limitations are acceptable for spidev, which only needs a registered spi_device to expose a character device to userspace. Only devices created via new_device can be removed through delete_device; DT and platform devices are unaffected. The sysfs attributes are gated behind CONFIG_SPI_DYNAMIC since this feature adds a new way of dynamically instantiating and removing SPI devices, and the add_lock locking in spi_unregister_controller() is already conditional on CONFIG_SPI_DYNAMIC. The userspace sysfs group is created manually as the last step of spi_register_controller() and removed as the first step of spi_unregister_controller(). Removing the group before taking add_lock means kernfs_drain() completes any in-flight new_device_store()/delete_device_store() calls before add_lock is acquired, so unregister never blocks on a store that is itself waiting for add_lock and no store can be touching an spi_device that is about to be torn down. Non-sysfs callers of __spi_add_device() (DT/ACPI dynamic add, ancillary registration) continue to be protected by the pre-existing !device_is_registered(&ctlr->dev) check added in commit ddf75be47ca7 ("spi: Prevent adding devices below an unregistering controller"): device_del(&ctlr->dev) runs inside add_lock in spi_unregister_controller() so state_in_sysfs flips to 0 before add_lock is released. Link: https://lore.kernel.org/linux-tegra/909f0c92-d110-4253-903e-5c81e21e12c9@nvidia.com/ Upstream-Status: Backport [e0db3f62dbe6bd683a3533fff955165da1c143f7] Signed-off-by: Vishwaroop A Link: https://patch.msgid.link/20260803104614.2548375-2-va@nvidia.com Signed-off-by: Mark Brown --- drivers/spi/spi.c | 246 ++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/spi/spi.h | 18 ++++ 2 files changed, 264 insertions(+) diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c index 05c1cc12cfc2..820f2299edc5 100644 --- a/drivers/spi/spi.c +++ b/drivers/spi/spi.c @@ -44,6 +44,7 @@ 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); @@ -301,6 +302,192 @@ 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, @@ -3221,6 +3408,9 @@ 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; @@ -3516,6 +3706,29 @@ 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: @@ -3591,10 +3804,43 @@ 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 e5649cd8656f..e256d11c852d 100644 --- a/include/linux/spi/spi.h +++ b/include/linux/spi/spi.h @@ -177,6 +177,8 @@ 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. @@ -250,6 +252,10 @@ 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: @@ -553,6 +559,11 @@ extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 ch * @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 @@ -808,6 +819,13 @@ 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) -- cgit v1.2.3