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    Subject[PATCH] spi: Add a sysfs interface to instantiate devices
    Date
    Add a sysfs interface to instantiate and delete SPI devices using the
    spidev driver. This can be used when developing a driver on a
    self-soldered board which doesn't yet have proper SPI device declaration
    at the platform level, and presumably for various debugging situations.

    Inspired by 99cd8e25875a ("i2c: Add a sysfs interface to instantiate
    devices").

    Signed-off-by: Kyle Roeschley <kyle.roeschley@ni.com>
    ---
    Documentation/spi/spi-summary | 14 ++++++++
    drivers/spi/spi.c | 78 +++++++++++++++++++++++++++++++++++++++++++
    include/linux/spi/spi.h | 3 ++
    3 files changed, 95 insertions(+)

    diff --git a/Documentation/spi/spi-summary b/Documentation/spi/spi-summary
    index 1721c1b570c3..51d9747c4426 100644
    --- a/Documentation/spi/spi-summary
    +++ b/Documentation/spi/spi-summary
    @@ -339,6 +339,20 @@ up the spi bus master, and will likely need spi_new_device() to provide the
    board info based on the board that was hotplugged. Of course, you'd later
    call at least spi_unregister_device() when that board is removed.

    +Alternatively, a sysfs interface was added to let the user create devices which
    +using the spidev driver. This interface is made of 2 attribute files which are
    +created in every SPI master directory: new_device and delete_device. Both files
    +are write only and you must write the decimal SPI chip select number to them in
    +order to properly instantiate or delete a SPI device. As no two devices can be
    +attached to the same master with the same chip select line, the chip select
    +number is sufficient to uniquely identify the device to be deleted.
    +
    +Example:
    +# echo 1 > /sys/class/spi_master/spi0/new_device
    +
    +In general, this interface should only be used when in-kernel device
    +declaration can't be done.
    +
    When Linux includes support for MMC/SD/SDIO/DataFlash cards through SPI, those
    configurations will also be dynamic. Fortunately, such devices all support
    basic device identification probes, so they should hotplug normally.
    diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
    index b33a727a0158..648ccdf359f9 100644
    --- a/drivers/spi/spi.c
    +++ b/drivers/spi/spi.c
    @@ -242,8 +242,85 @@ static const struct attribute_group spi_controller_statistics_group = {
    .attrs = spi_controller_statistics_attrs,
    };

    +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;
    + struct spi_board_info bi = {
    + .modalias = "spidev",
    + .max_speed_hz = ctlr->max_speed_hz,
    + };
    +
    + if (kstrtou16(buf, 0, &bi.chip_select) < 0)
    + return -EINVAL;
    +
    + spi = spi_new_device(ctlr, &bi);
    + if (!spi) {
    + dev_err(dev, "can't create new device\n");
    + return -ENXIO;
    + }
    +
    + mutex_lock(&ctlr->bus_lock_mutex);
    + list_add_tail(&spi->userspace_device, &ctlr->userspace_devices);
    + mutex_unlock(&ctlr->bus_lock_mutex);
    +
    + dev_info(dev, "created spidev device %s\n", dev_name(&spi->dev));
    +
    + 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;
    + int ret = -ENXIO;
    + u16 cs;
    +
    + if (kstrtou16(buf, 0, &cs) < 0)
    + return -EINVAL;
    +
    + mutex_lock(&ctlr->bus_lock_mutex);
    + list_for_each_entry_safe(spi, next, &ctlr->userspace_devices,
    + userspace_device) {
    + if (spi->chip_select != cs)
    + continue;
    +
    + dev_info(dev, "deleting spidev device %s\n",
    + dev_name(&spi->dev));
    + list_del(&spi->userspace_device);
    + spi_unregister_device(spi);
    + ret = count;
    + break;
    + }
    + mutex_unlock(&ctlr->bus_lock_mutex);
    +
    + if (ret == -ENXIO)
    + dev_err(dev, "can't find spidev device %u in list\n", cs);
    +
    + return ret;
    +}
    +static DEVICE_ATTR_WO(delete_device);
    +
    +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_master_groups[] = {
    &spi_controller_statistics_group,
    + &spi_controller_userspace_group,
    NULL,
    };

    @@ -2129,6 +2206,7 @@ int spi_register_controller(struct spi_controller *ctlr)
    return id;
    ctlr->bus_num = id;
    }
    + INIT_LIST_HEAD(&ctlr->userspace_devices);
    INIT_LIST_HEAD(&ctlr->queue);
    spin_lock_init(&ctlr->queue_lock);
    spin_lock_init(&ctlr->bus_lock_spinlock);
    diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
    index bc6bb325d1bf..f7255745326d 100644
    --- a/include/linux/spi/spi.h
    +++ b/include/linux/spi/spi.h
    @@ -172,6 +172,8 @@ struct spi_device {
    /* the statistics */
    struct spi_statistics statistics;

    + struct list_head userspace_device;
    +
    /*
    * likely need more hooks for more protocol options affecting how
    * the controller talks to each chip, like:
    @@ -410,6 +412,7 @@ struct spi_controller {
    struct device dev;

    struct list_head list;
    + struct list_head userspace_devices;

    /* other than negative (== assign one dynamically), bus_num is fully
    * board-specific. usually that simplifies to being SOC-specific.
    --
    2.15.1
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