netdev - [PATCH net-next 10/14] net: ethernet: mtk_eth_soc: cache HW pointer of last freed TX descriptor

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Message-Id: <20210422040914.47788-11-ilya.lipnitskiy@gmail.com>
Date:   Wed, 21 Apr 2021 21:09:10 -0700
From:   Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
To:     Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Cc:     Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
Subject: [PATCH net-next 10/14] net: ethernet: mtk_eth_soc: cache HW pointer of last freed TX descriptor

From: Felix Fietkau <nbd@....name>

The value is only updated by the CPU, so it is cheaper to access from the
ring data structure than from a hardware register.

Signed-off-by: Felix Fietkau <nbd@....name>
Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 8 ++++----
 drivers/net/ethernet/mediatek/mtk_eth_soc.h | 2 ++
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 043ab5446524..01ad10c76d53 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -1362,7 +1362,7 @@ static int mtk_poll_tx_qdma(struct mtk_eth *eth, int budget,
 	struct mtk_tx_buf *tx_buf;
 	u32 cpu, dma;
 
-	cpu = mtk_r32(eth, MTK_QTX_CRX_PTR);
+	cpu = ring->last_free_ptr;
 	dma = mtk_r32(eth, MTK_QTX_DRX_PTR);
 
 	desc = mtk_qdma_phys_to_virt(ring, cpu);
@@ -1396,6 +1396,7 @@ static int mtk_poll_tx_qdma(struct mtk_eth *eth, int budget,
 		cpu = next_cpu;
 	}
 
+	ring->last_free_ptr = cpu;
 	mtk_w32(eth, cpu, MTK_QTX_CRX_PTR);
 
 	return budget;
@@ -1596,6 +1597,7 @@ static int mtk_tx_alloc(struct mtk_eth *eth)
 	atomic_set(&ring->free_count, MTK_DMA_SIZE - 2);
 	ring->next_free = &ring->dma[0];
 	ring->last_free = &ring->dma[MTK_DMA_SIZE - 1];
+	ring->last_free_ptr = (u32)(ring->phys + ((MTK_DMA_SIZE - 1) * sz));
 	ring->thresh = MAX_SKB_FRAGS;
 
 	/* make sure that all changes to the dma ring are flushed before we
@@ -1609,9 +1611,7 @@ static int mtk_tx_alloc(struct mtk_eth *eth)
 		mtk_w32(eth,
 			ring->phys + ((MTK_DMA_SIZE - 1) * sz),
 			MTK_QTX_CRX_PTR);
-		mtk_w32(eth,
-			ring->phys + ((MTK_DMA_SIZE - 1) * sz),
-			MTK_QTX_DRX_PTR);
+		mtk_w32(eth, ring->last_free_ptr, MTK_QTX_DRX_PTR);
 		mtk_w32(eth, (QDMA_RES_THRES << 8) | QDMA_RES_THRES,
 			MTK_QTX_CFG(0));
 	} else {
diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.h b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
index a8d388b02558..214da569e869 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.h
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
@@ -642,6 +642,7 @@ struct mtk_tx_buf {
  * @phys:		The physical addr of tx_buf
  * @next_free:		Pointer to the next free descriptor
  * @last_free:		Pointer to the last free descriptor
+ * @last_free_ptr:	Hardware pointer value of the last free descriptor
  * @thresh:		The threshold of minimum amount of free descriptors
  * @free_count:		QDMA uses a linked list. Track how many free descriptors
  *			are present
@@ -652,6 +653,7 @@ struct mtk_tx_ring {
 	dma_addr_t phys;
 	struct mtk_tx_dma *next_free;
 	struct mtk_tx_dma *last_free;
+	u32 last_free_ptr;
 	u16 thresh;
 	atomic_t free_count;
 	int dma_size;
-- 
2.31.1