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

From: Ilya Lipnitskiy
Date: Thu Apr 22 2021 - 00:10:45 EST


From: Felix Fietkau <nbd@xxxxxxxx>

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@xxxxxxxx>
Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@xxxxxxxxx>
---
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