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Mon, 27 Jul 2026 20:05:47 -0700 From: Vishwaroop A To: Mark Brown CC: , , Jon Hunter , Thierry Reding , "Suresh Mangipudi" , , "Vishwaroop A" Subject: [PATCH v7 1/2] spi: add new_device/delete_device sysfs interface Date: Tue, 28 Jul 2026 03:05:40 +0000 Message-ID: <20260728030541.2279518-2-va@nvidia.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20260728030541.2279518-1-va@nvidia.com> References: <20260728030541.2279518-1-va@nvidia.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN2PEPF00004FBE:EE_|DS7PR12MB8203:EE_ X-MS-Office365-Filtering-Correlation-Id: 3e2e0b20-4c0d-4bbd-e3fd-08deec55260d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|30052699003|82310400026|23010399003|376014|1800799024|36860700016|18002099003|22082099003|11063799006|10067099003|56012099006|3023799007|6133799003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: xCqU94mhjEObk293x0fWIj9XbiDpIrwX7ZsnDL27IjNX3w9ixxyAESwVZz5GfCqBODyf9POjyyhPj61W4UG/KAsg8sQE8WuJR7Ht0t44vyXr1lsZ+9Zyo1lLFBIezZS1t28a3Vcn4OsWTKLOygeKdNN/CCsh2Z8GbjtkqcJB8ZjRo3sosPUskK0tIDqfMMYB36Q1LfR2qZhxEhZkg2aej8P0iEce+Ydn5TYgTOR8+Ow0KthQVXZi/qPsbDVJJH49/4kRRoW5MZFd43xyAQ8+339LlwnyU1Pb8xMFfvSu9skNmjxHodbKXAU3m87MCKY+ViwgqG7fEYkminT4IjD3xzH+3lupUgbA0ew+rikAYNrJCAq4upRmKkbCYYjlG6bQH/NbkrxATmCTk0cUbTiyQ1CUzjd6TCsJlt/5nfyxeuQnMXUHnVqsFBq8QlxpJa/g X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Jul 2026 03:05:58.6134 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 3e2e0b20-4c0d-4bbd-e3fd-08deec55260d X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN2PEPF00004FBE.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR12MB8203 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. A 'dead' flag on spi_controller prevents new device registration and list insertion after spi_unregister_controller() begins tearing down the controller. This avoids: 1. An ABBA deadlock between add_lock and the kernfs active reference held by sysfs store callbacks. add_lock is released before device_del() so that in-flight sysfs operations can drain. 2. Orphaned devices that could slip through after the userspace_clients cleanup but before device_del(). 3. Use-after-free if __unregister frees a device that new_device_store() still references. An extra get_device() before spi_add_device() holds the device alive. Link: https://lore.kernel.org/linux-tegra/909f0c92-d110-4253-903e-5c81e21e12c9@nvidia.com/ Signed-off-by: Vishwaroop A --- drivers/spi/spi.c | 270 +++++++++++++++++++++++++++++++++++++++- include/linux/spi/spi.h | 23 ++++ 2 files changed, 287 insertions(+), 6 deletions(-) diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c index d9e6b4b87c89..6a6c822cc04e 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); @@ -297,11 +298,214 @@ 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 res, status; + + blank = strchr(buf, ' '); + if (!blank) { + dev_err(dev, "%s: Missing parameters\n", "new_device"); + return -EINVAL; + } + + if (blank == buf || blank - buf > SPI_NAME_SIZE - 1) { + dev_err(dev, "%s: Invalid device name\n", "new_device"); + 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). + */ + res = sscanf(++blank, "%u %u %u", + &chip_select, &max_speed_hz, &mode); + if (res < 1) { + dev_err(dev, "%s: Can't parse chip select\n", "new_device"); + 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, "%s: Chip select %u out of range (num_chipselect=%u)\n", + "new_device", 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, "%s: Invalid mode bits 0x%x\n", "new_device", + 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; + } + + /* + * Serialise against spi_unregister_controller() via add_lock so + * that the dead check, __spi_add_device() and list insertion are + * atomic with respect to controller teardown. + */ + mutex_lock(&ctlr->add_lock); + + if (ctlr->dead) { + mutex_unlock(&ctlr->add_lock); + spi_dev_put(spi); + return -ENODEV; + } + + 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, "%s: Instantiated device %s at CS%u\n", + "new_device", 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, "%s: Can't parse chip select\n", "delete_device"); + return -EINVAL; + } + if (res > 1 && end != '\n') { + dev_err(dev, "%s: Extra parameters\n", "delete_device"); + 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, "%s: Deleting device %s at CS%u\n", + "delete_device", 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, "%s: Can't find device in list\n", + "delete_device"); + 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, +}; + +/* + * spi_controller_userspace_group is deliberately NOT listed here. Attaching + * it via ctlr->dev.groups would expose new_device/delete_device the moment + * device_add() runs, i.e. before spi_register_controller() has finished + * bringing up the queue, matching boardinfo and registering DT/ACPI + * children. It is instead created manually as the last step of + * spi_register_controller() and torn down as the first step of + * spi_unregister_controller(). + */ +static const struct attribute_group *spi_controller_groups[] = { + &spi_controller_statistics_group, + NULL, +}; + +#else /* !CONFIG_SPI_DYNAMIC */ + static const struct attribute_group *spi_controller_groups[] = { &spi_controller_statistics_group, NULL, }; +#endif /* CONFIG_SPI_DYNAMIC */ + static void spi_statistics_add_transfer_stats(struct spi_statistics __percpu *pcpu_stats, struct spi_transfer *xfer, struct spi_message *msg) @@ -729,10 +933,10 @@ static int __spi_add_device(struct spi_device *spi, struct spi_device *parent) return status; /* Controller may unregister concurrently */ - if (IS_ENABLED(CONFIG_SPI_DYNAMIC) && - !device_is_registered(&ctlr->dev)) { +#if IS_ENABLED(CONFIG_SPI_DYNAMIC) + if (ctlr->dead) return -ENODEV; - } +#endif if (ctlr->cs_gpiods) { for (idx = 0; idx < spi->num_chipselect; idx++) { @@ -3259,6 +3463,9 @@ 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 +3759,24 @@ 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 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. + */ + 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; +#endif + return 0; del_ctrl: @@ -3616,12 +3841,48 @@ 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) + /* + * Mark dead and drain userspace_clients before __unregister, + * since spi_unregister_device() doesn't do list_del() itself. + * With the userspace sysfs group already removed above, no new + * entries can appear in this list. + */ + ctlr->dead = true; + 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); + if (IS_ENABLED(CONFIG_SPI_DYNAMIC)) + mutex_unlock(&ctlr->add_lock); + /* First make sure that this controller was ever added */ mutex_lock(&board_lock); found = idr_find(&spi_controller_idr, id); @@ -3641,9 +3902,6 @@ void spi_unregister_controller(struct spi_controller *ctlr) if (found == ctlr) idr_remove(&spi_controller_idr, id); mutex_unlock(&board_lock); - - if (IS_ENABLED(CONFIG_SPI_DYNAMIC)) - mutex_unlock(&ctlr->add_lock); } EXPORT_SYMBOL_GPL(spi_unregister_controller); diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h index 4c285d3ede1d..628b3466cdf5 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 +561,14 @@ 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 + * @dead: set to true under @add_lock when spi_unregister_controller() + * begins teardown; prevents __spi_add_device() from racing new + * device registrations against controller shutdown * * 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 +821,15 @@ 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; + /* Set true under @add_lock once spi_unregister_controller() has begun teardown */ + bool dead; +#endif }; static inline void *spi_controller_get_devdata(struct spi_controller *ctlr) -- 2.17.1