1 files changed, 29 insertions, 11 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 964124b60db2..75e86865234c 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -226,10 +226,11 @@ EXPORT_SYMBOL_GPL(spi_alloc_device);
  * Companion function to spi_alloc_device.  Devices allocated with
  * spi_alloc_device can be added onto the spi bus with this function.
  *
- * Returns 0 on success; non-zero on failure
+ * Returns 0 on success; negative errno on failure
  */
 int spi_add_device(struct spi_device *spi)
 {
+        static DEFINE_MUTEX(spi_add_lock);
         struct device *dev = spi->master->dev.parent;
         int status;
 
@@ -246,26 +247,43 @@ int spi_add_device(struct spi_device *spi)
                         "%s.%u", spi->master->dev.bus_id,
                         spi->chip_select);
 
-        /* drivers may modify this initial i/o setup */
+
+        /* We need to make sure there's no other device with this
+         * chipselect **BEFORE** we call setup(), else we'll trash
+         * its configuration.  Lock against concurrent add() calls.
+         */
+        mutex_lock(&spi_add_lock);
+
+        if (bus_find_device_by_name(&spi_bus_type, NULL, spi->dev.bus_id)
+                        != NULL) {
+                dev_err(dev, "chipselect %d already in use\n",
+                                spi->chip_select);
+                status = -EBUSY;
+                goto done;
+        }
+
+        /* Drivers may modify this initial i/o setup, but will
+         * normally rely on the device being setup.  Devices
+         * using SPI_CS_HIGH can't coexist well otherwise...
+         */
         status = spi->master->setup(spi);
         if (status < 0) {
                 dev_err(dev, "can't %s %s, status %d\n",
                                 "setup", spi->dev.bus_id, status);
-                return status;
+                goto done;
         }
 
-        /* driver core catches callers that misbehave by defining
-         * devices that already exist.
-         */
+        /* Device may be bound to an active driver when this returns */
         status = device_add(&spi->dev);
-        if (status < 0) {
+        if (status < 0)
                 dev_err(dev, "can't %s %s, status %d\n",
                                 "add", spi->dev.bus_id, status);
-                return status;
-        }
+        else
+                dev_dbg(dev, "registered child %s\n", spi->dev.bus_id);
 
-        dev_dbg(dev, "registered child %s\n", spi->dev.bus_id);
-        return 0;
+done:
+        mutex_unlock(&spi_add_lock);
+        return status;
 }
 EXPORT_SYMBOL_GPL(spi_add_device);