[PATCH 7/9] dmaengine: dw-edma: eDMA: Add memory barrier before starting the DMA transfer in remote setup

["Köry Maincent" <kory.maincent@bootlin.com>]

From: Kory Maincent <kory.maincent@bootlin.com>

The Linked list element and pointer are not stored in the same memory as
the eDMA controller register. If the doorbell register is toggled before
the full write of the linked list a race condition error can appears.
In remote setup we can only use a readl to the memory to assured the full
write has occurred.

Fixes: 7e4b8a4fbe2c ("dmaengine: Add Synopsys eDMA IP version 0 support")
Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
---
 drivers/dma/dw-edma/dw-edma-v0-core.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/dma/dw-edma/dw-edma-v0-core.c b/drivers/dma/dw-edma/dw-edma-v0-core.c
index b38786f0ad79..2e872d6f2c04 100644
--- a/drivers/dma/dw-edma/dw-edma-v0-core.c
+++ b/drivers/dma/dw-edma/dw-edma-v0-core.c
@@ -412,6 +412,15 @@ static void dw_edma_v0_core_start(struct dw_edma_chunk *chunk, bool first)
 		SET_CH_32(dw, chan->dir, chan->id, llp.msb,
 			  upper_32_bits(chunk->ll_region.paddr));
 	}
+
+	if (!(chunk->chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
+		/* Make sure Linked List has been written.
+		 * Linux memory barriers don't cater for what's required here.
+		 * What's required is what's here - a read of the linked
+		 * list region.
+		 */
+		readl(chunk->ll_region.vaddr.io);
+
 	/* Doorbell */
 	SET_RW_32(dw, chan->dir, doorbell,
 		  FIELD_PREP(EDMA_V0_DOORBELL_CH_MASK, chan->id));
-- 
2.25.1