dmaengine: mv_xor_v2: fix tx_submit() implementation

The mv_xor_v2_tx_submit() gets the next available HW descriptor by
calling mv_xor_v2_get_desq_write_ptr(), which reads a HW register
telling the next available HW descriptor. This was working fine when HW
descriptors were issued for processing directly in tx_submit().

However, as part of the review process of the driver, a change was
requested to move the actual kick-off of HW descriptors processing to
->issue_pending(). Due to this, reading the HW register to know the next
available HW descriptor no longer works.

So instead of using this HW register, we implemented a software index
pointing to the next available HW descriptor.

Fixes: 19a340b1 ("dmaengine: mv_xor_v2: new driver")
Cc: <stable@vger.kernel.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/mv_xor_v2.c

@@ -161,6 +161,7 @@ struct mv_xor_v2_device {
 	struct mv_xor_v2_sw_desc *sw_desq;
 	int desc_size;
 	unsigned int npendings;
+	unsigned int hw_queue_idx;
 };
 
 /**
@@ -213,18 +214,6 @@ static void mv_xor_v2_set_data_buffers(struct mv_xor_v2_device *xor_dev,
 	}
 }
 
-/*
- * Return the next available index in the DESQ.
- */
-static int mv_xor_v2_get_desq_write_ptr(struct mv_xor_v2_device *xor_dev)
-{
-	/* read the index for the next available descriptor in the DESQ */
-	u32 reg = readl(xor_dev->dma_base + MV_XOR_V2_DMA_DESQ_ALLOC_OFF);
-
-	return ((reg >> MV_XOR_V2_DMA_DESQ_ALLOC_WRPTR_SHIFT)
-		& MV_XOR_V2_DMA_DESQ_ALLOC_WRPTR_MASK);
-}
-
 /*
  * notify the engine of new descriptors, and update the available index.
  */
@@ -306,7 +295,6 @@ static irqreturn_t mv_xor_v2_interrupt_handler(int irq, void *data)
 static dma_cookie_t
 mv_xor_v2_tx_submit(struct dma_async_tx_descriptor *tx)
 {
-	int desq_ptr;
 	void *dest_hw_desc;
 	dma_cookie_t cookie;
 	struct mv_xor_v2_sw_desc *sw_desc =
@@ -322,15 +310,15 @@ mv_xor_v2_tx_submit(struct dma_async_tx_descriptor *tx)
 	spin_lock_bh(&xor_dev->lock);
 	cookie = dma_cookie_assign(tx);
 
-	/* get the next available slot in the DESQ */
-	desq_ptr = mv_xor_v2_get_desq_write_ptr(xor_dev);
-
 	/* copy the HW descriptor from the SW descriptor to the DESQ */
-	dest_hw_desc = xor_dev->hw_desq_virt + desq_ptr;
+	dest_hw_desc = xor_dev->hw_desq_virt + xor_dev->hw_queue_idx;
 
 	memcpy(dest_hw_desc, &sw_desc->hw_desc, xor_dev->desc_size);
 
 	xor_dev->npendings++;
+	xor_dev->hw_queue_idx++;
+	if (xor_dev->hw_queue_idx >= MV_XOR_V2_DESC_NUM)
+		xor_dev->hw_queue_idx = 0;
 
 	spin_unlock_bh(&xor_dev->lock);