[PATCH] net: mvpp2: avoid bouncing buffers

From: Brian Brooks
Date: Sun Aug 19 2018 - 22:48:19 EST


Some memory regions used by this device need to share the same
upper 8 bits of the 40-bit bus address. Currently, a coherent
DMA mask of 32 bits is used so that dma_alloc_coherent() regions
have the same upper 8 bits. Packet buffers are not allocated via
DMA APIs, and the device does not require these memory regions
to have the same upper 8 bits. However, packet buffers are being
bounced during streaming mappings because streaming and coherent
DMA are using the same DMA mask, i.e. dev->dma_mask points to
dev->coherent_dma_mask.

Avoid bouncing packet buffers by ensuring streaming DMA uses a
mask of 40 bits and coherent DMA uses a mask of 32 bits. iperf3
shows throughput increases from 4.04 Gbps to 9.14 Gbps.

Signed-off-by: Brian Brooks <brian.brooks@xxxxxxxxxx>
---
drivers/net/ethernet/marvell/mvpp2/mvpp2.h | 3 +++
drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 6 ++++++
2 files changed, 9 insertions(+)

diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2.h b/drivers/net/ethernet/marvell/mvpp2/mvpp2.h
index def00dc3eb4e..3eb0c3ede8d2 100644
--- a/drivers/net/ethernet/marvell/mvpp2/mvpp2.h
+++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2.h
@@ -676,6 +676,9 @@ struct mvpp2 {
struct clk *mg_core_clk;
struct clk *axi_clk;

+ /* DMA mask for streaming mappings */
+ u64 dma_mask;
+
/* List of pointers to port structures */
int port_count;
struct mvpp2_port *port_list[MVPP2_MAX_PORTS];
diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
index 0319ed9ef8b8..3a190c489589 100644
--- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
+++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
@@ -5126,6 +5126,12 @@ static int mvpp2_probe(struct platform_device *pdev)
}

if (priv->hw_version == MVPP22) {
+ /* Platform code may have set dev->dma_mask to point
+ * to dev->coherent_dma_mask, but we want to ensure
+ * they take different values due to comment below.
+ */
+ pdev->dev.dma_mask = &priv->dma_mask;
+
err = dma_set_mask(&pdev->dev, MVPP2_DESC_DMA_MASK);
if (err)
goto err_axi_clk;
--
2.17.1