carma-fpga: fix lockdep warning

Lockdep occasionally complains with the message:
INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected

This is caused by calling videobuf_dma_unmap() under spin_lock_irq(). To
fix the warning, we drop the lock before unmapping and freeing the
buffer.

Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 11 insertions, 2 deletions

diff --git a/drivers/misc/carma/carma-fpga.c b/drivers/misc/carma/carma-fpga.c
index 14e974b2a781..4fd896deda0d 100644
--- a/drivers/misc/carma/carma-fpga.c
+++ b/drivers/misc/carma/carma-fpga.c
@@ -1079,6 +1079,7 @@ static ssize_t data_read(struct file *filp, char __user *ubuf, size_t count,
         struct fpga_reader *reader = filp->private_data;
         struct fpga_device *priv = reader->priv;
         struct list_head *used = &priv->used;
+        bool drop_buffer = false;
         struct data_buf *dbuf;
         size_t avail;
         void *data;
@@ -1166,10 +1167,12 @@ have_buffer:
          * One of two things has happened, the device is disabled, or the
          * device has been reconfigured underneath us. In either case, we
          * should just throw away the buffer.
+         *
+         * Lockdep complains if this is done under the spinlock, so we
+         * handle it during the unlock path.
          */
         if (!priv->enabled || dbuf->size != priv->bufsize) {
-                videobuf_dma_unmap(priv->dev, &dbuf->vb);
-                data_free_buffer(dbuf);
+                drop_buffer = true;
                 goto out_unlock;
         }
 
@@ -1178,6 +1181,12 @@ have_buffer:
 
 out_unlock:
         spin_unlock_irq(&priv->lock);
+
+        if (drop_buffer) {
+                videobuf_dma_unmap(priv->dev, &dbuf->vb);
+                data_free_buffer(dbuf);
+        }
+
         return count;
 }