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Sat, 25 Apr 2026 10:34:26 -0700 From: Vishwaroop A To: Mark Brown CC: , , "Thierry Reding" , Jonathan Hunter , Francesco Dolcini , , Subject: [PATCH v2 1/2] spi: add new_device/delete_device sysfs interface Date: Sat, 25 Apr 2026 17:34:24 +0000 Message-ID: <20260425173425.622042-2-va@nvidia.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20260425173425.622042-1-va@nvidia.com> References: <20260420031417.291442-1-va@nvidia.com> <20260425173425.622042-1-va@nvidia.com> Precedence: bulk X-Mailing-List: linux-spi@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: CO1PEPF000075ED:EE_|DS2PR12MB9709:EE_ X-MS-Office365-Filtering-Correlation-Id: 98ec3cb3-a4d1-4829-6eb2-08dea2f0ecfd X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|30052699003|1800799024|82310400026|36860700016|13003099007|22082099003|56012099003|18002099003; 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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. Link: https://lore.kernel.org/linux-tegra/909f0c92-d110-4253-903e-5c81e21e12c9@nvidia.com/ Signed-off-by: Vishwaroop A --- drivers/spi/spi.c | 190 ++++++++++++++++++++++++++++++++++++++++ include/linux/spi/spi.h | 10 +++ 2 files changed, 200 insertions(+) diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c index 7001f5dce8bd..916741690462 100644 --- a/drivers/spi/spi.c +++ b/drivers/spi/spi.c @@ -296,8 +296,178 @@ static const struct attribute_group spi_controller_statistics_group = { .attrs = spi_controller_statistics_attrs, }; +static void spi_dev_set_name(struct spi_device *spi); +static int __spi_add_device(struct spi_device *spi, struct spi_device *parent); + +/* + * 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; + } + + /* + * Use __spi_add_device() directly rather than spi_add_device() + * so we can hold add_lock across both the device registration + * and the list insertion. Without this, spi_unregister_controller() + * could run between the two operations: the device would be known + * to the core (so __unregister iterates over it) but not yet on + * the userspace_clients list, leading to a double-free or a + * dangling list entry. + */ + spi_dev_set_name(spi); + + mutex_lock(&ctlr->add_lock); + status = __spi_add_device(spi, NULL); + if (status) { + mutex_unlock(&ctlr->add_lock); + spi_dev_put(spi); + return status; + } + + mutex_lock(&ctlr->userspace_clients_lock); + list_add_tail(&spi->userspace_node, &ctlr->userspace_clients); + mutex_unlock(&ctlr->userspace_clients_lock); + 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_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, }; @@ -3256,6 +3426,8 @@ 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); + mutex_init(&ctlr->userspace_clients_lock); + INIT_LIST_HEAD(&ctlr->userspace_clients); ctlr->bus_num = -1; ctlr->num_chipselect = 1; ctlr->num_data_lanes = 1; @@ -3633,6 +3805,24 @@ void spi_unregister_controller(struct spi_controller *ctlr) if (IS_ENABLED(CONFIG_SPI_DYNAMIC)) mutex_lock(&ctlr->add_lock); + /* + * Remove devices created via the sysfs new_device interface. + * These must be explicitly removed before device_for_each_child() + * below because spi_unregister_device() does not remove devices + * from the userspace_clients list; freeing them without list_del() + * first would leave dangling pointers in that list. + */ + mutex_lock(&ctlr->userspace_clients_lock); + 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); + 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 7587b1c5d7ec..63c267ca9730 100644 --- a/include/linux/spi/spi.h +++ b/include/linux/spi/spi.h @@ -250,6 +250,9 @@ struct spi_device { u8 rx_lane_map[SPI_DEVICE_DATA_LANE_CNT_MAX]; u8 num_rx_lanes; + /* Entry on controller's userspace_clients list */ + struct list_head userspace_node; + /* * Likely need more hooks for more protocol options affecting how * the controller talks to each chip, like: @@ -554,6 +557,9 @@ 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 +815,10 @@ struct spi_controller { bool queue_empty; bool must_async; bool defer_optimize_message; + + /* List of SPI devices created via sysfs new_device interface */ + struct list_head userspace_clients; + struct mutex userspace_clients_lock; }; static inline void *spi_controller_get_devdata(struct spi_controller *ctlr) -- 2.17.1