dmaengine: imx-sdma: fix cyclic buffer race condition

Assign buffer ownership to SDMA after invoking descriptor callback to
make sure that SDMA does not write to the buffer before it is read by
the CPU.

Signed-off-by: Tomasz Moń <tomasz.mon@camlingroup.com>
Link: https://lore.kernel.org/r/20220117091955.1038937-2-tomasz.mon@camlingroup.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: Tomasz Moń

drivers/dma/imx-sdma.c

@@ -847,7 +847,6 @@ 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;
@@ -862,6 +861,9 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac)
 		dmaengine_desc_get_callback_invoke(&desc->vd.tx, NULL);
 		spin_lock(&sdmac->vc.lock);
 
+		/* Assign buffer ownership to SDMA */
+		bd->mode.status |= BD_DONE;
+
 		if (error)
 			sdmac->status = old_status;
 	}