dmaengine: imx-sdma: fix buffer ownership

BD_DONE flag marks ownership of the buffer. When 1 SDMA owns the
buffer, when 0 ARM owns it. When processing the buffers in
sdma_update_channel_loop the ownership of the currently processed
buffer was set to SDMA again before running the callback function of
the buffer and while the sdma script may be running in parallel. So
there was the possibility to get the buffer overwritten by SDMA before
it has been processed by kernel leading to kind of random errors in the
upper layers, e.g. bluetooth.

Signed-off-by: Philipp Puschmann <philipp.puschmann@emlix.com>

drivers/dma/imx-sdma.c

@@ -802,7 +802,6 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac)
 		*/
 
 		desc->chn_real_count = bd->mode.count;
-		bd->mode.status |= BD_DONE;
 		bd->mode.count = desc->period_len;
 		desc->buf_ptail = desc->buf_tail;
 		desc->buf_tail = (desc->buf_tail + 1) % desc->num_bd;
@@ -817,6 +816,9 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac)
 		dmaengine_desc_get_callback_invoke(&desc->vd.tx, NULL);
 		spin_lock(&sdmac->vc.lock);
 
+		dma_wb();
+		bd->mode.status |= BD_DONE;
+
 		if (error)
 			sdmac->status = old_status;
 	}