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Sun, 17 May 2026 13:16:03 -0700 From: Vishwaroop A To: , CC: , , , , , Subject: [PATCH v5 1/2] spi: add new_device/delete_device sysfs interface Date: Sun, 17 May 2026 20:16:01 +0000 Message-ID: <20260517201602.498135-2-va@nvidia.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20260517201602.498135-1-va@nvidia.com> References: <20260517201602.498135-1-va@nvidia.com> Precedence: bulk X-Mailing-List: linux-doc@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: CH1PEPF0000AD79:EE_|PH7PR12MB5712:EE_ X-MS-Office365-Filtering-Correlation-Id: b11d68bb-cd1c-48ff-9df9-08deb451244e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|36860700016|1800799024|30052699003|82310400026|3023799003|56012099003|22082099003|18002099003|11063799003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.118.232;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc7edge1.nvidia.com;CAT:NONE;SFS:(13230040)(376014)(36860700016)(1800799024)(30052699003)(82310400026)(3023799003)(56012099003)(22082099003)(18002099003)(11063799003);DIR:OUT;SFP:1101; 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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 | 217 ++++++++++++++++++++++++++++++++++++++-- include/linux/spi/spi.h | 13 +++ 2 files changed, 224 insertions(+), 6 deletions(-) diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c index 7001f5dce8bd..9042c19746b8 100644 --- a/drivers/spi/spi.c +++ b/drivers/spi/spi.c @@ -296,11 +296,188 @@ 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]; + u16 chip_select; + u32 max_speed_hz = 0; + u32 mode = 0; + char *blank; + int n, res, status; + + blank = strchr(buf, ' '); + if (!blank) { + dev_err(dev, "%s: Missing parameters\n", "new_device"); + return -EINVAL; + } + + if (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, "%hu %u %u%n", + &chip_select, &max_speed_hz, &mode, &n); + if (res < 1) { + dev_err(dev, "%s: Can't parse chip select\n", "new_device"); + return -EINVAL; + } + + if (chip_select >= ctlr->num_chipselect) { + dev_err(dev, "%s: Chip select %u >= max %u\n", "new_device", + chip_select, ctlr->num_chipselect); + 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; + } + + /* Extra ref so concurrent __unregister cannot free the device */ + get_device(&spi->dev); + + status = spi_add_device(spi); + if (status) { + put_device(&spi->dev); + spi_dev_put(spi); + return status; + } + + mutex_lock(&ctlr->userspace_clients_lock); + if (!ctlr->dead) { + list_add_tail(&spi->userspace_node, &ctlr->userspace_clients); + mutex_unlock(&ctlr->userspace_clients_lock); + put_device(&spi->dev); + dev_info(dev, "%s: Instantiated device %s at CS%u\n", + "new_device", modalias, chip_select); + return count; + } + mutex_unlock(&ctlr->userspace_clients_lock); + + /* + * Controller is dying; __unregister will clean up the device. + * Drop our extra ref and bail. + */ + put_device(&spi->dev); + return -ENODEV; +} +static DEVICE_ATTR_WO(new_device); + +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->userspace_clients_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->userspace_clients_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, +}; + static const struct attribute_group *spi_controller_groups[] = { &spi_controller_statistics_group, + &spi_controller_userspace_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) @@ -724,10 +901,10 @@ 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) { u8 cs; @@ -3256,6 +3433,10 @@ 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) + mutex_init(&ctlr->userspace_clients_lock); + INIT_LIST_HEAD(&ctlr->userspace_clients); +#endif ctlr->bus_num = -1; ctlr->num_chipselect = 1; ctlr->num_data_lanes = 1; @@ -3633,8 +3814,35 @@ void spi_unregister_controller(struct spi_controller *ctlr) if (IS_ENABLED(CONFIG_SPI_DYNAMIC)) mutex_lock(&ctlr->add_lock); + /* + * Mark dead and drain userspace_clients before __unregister, + * since spi_unregister_device() doesn't do list_del() itself. + */ +#if IS_ENABLED(CONFIG_SPI_DYNAMIC) + mutex_lock(&ctlr->userspace_clients_lock); + 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); + } + mutex_unlock(&ctlr->userspace_clients_lock); +#endif + device_for_each_child(&ctlr->dev, NULL, __unregister); + /* + * Release add_lock before device_del(): holding it would + * deadlock against kernfs_drain waiting for in-flight sysfs + * stores. ctlr->dead prevents new device registration. + */ + 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); @@ -3655,9 +3863,6 @@ void spi_unregister_controller(struct spi_controller *ctlr) idr_remove(&spi_controller_idr, id); mutex_unlock(&board_lock); - if (IS_ENABLED(CONFIG_SPI_DYNAMIC)) - mutex_unlock(&ctlr->add_lock); - /* * Release the last reference on the controller if its driver * has not yet been converted to devm_spi_alloc_host/target(). diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h index 7587b1c5d7ec..7a86749d2701 100644 --- a/include/linux/spi/spi.h +++ b/include/linux/spi/spi.h @@ -250,6 +250,10 @@ 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: @@ -554,6 +558,9 @@ 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 + * @userspace_clients_lock: mutex protecting @userspace_clients * * Each SPI controller can communicate with one or more @spi_device * children. These make a small bus, sharing MOSI, MISO and SCK signals @@ -809,6 +816,12 @@ struct spi_controller { bool queue_empty; bool must_async; bool defer_optimize_message; + +#if IS_ENABLED(CONFIG_SPI_DYNAMIC) + struct list_head userspace_clients; + struct mutex userspace_clients_lock; + bool dead; +#endif }; static inline void *spi_controller_get_devdata(struct spi_controller *ctlr) -- 2.17.1