linux-kernel - [PATCH] net: mvpp2: avoid bouncing buffers

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Date:   Sun, 19 Aug 2018 21:47:30 -0500
From:   Brian Brooks <brian.brooks@...aro.org>
To:     davem@...emloft.net
Cc:     antoine.tenart@...tlin.com, maxime.chevallier@...tlin.com,
        ymarkman@...vell.com, stefanc@...vell.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bjorn.topel@...el.com,
        brian.brooks@....com, Brian Brooks <brian.brooks@...aro.org>
Subject: [PATCH] net: mvpp2: avoid bouncing buffers

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@...aro.org>
---
 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