[net-next,v3,1/1] net: stmmac: Batch set RX OWN flag and other flags

[ende.tan@starfivetech.com]

From: Tan En De <ende.tan@starfivetech.com>

Minimize access to the RX descriptor by collecting all the flags in a
local variable and then updating the descriptor at once.

Signed-off-by: Tan En De <ende.tan@starfivetech.com>
---
v3:
- Use local variable to batch set the descriptor flags.
- This reduces the number of accesses to the descriptor.
v2: https://patchwork.kernel.org/project/netdevbpf/patch/20240821060307.46350-1-ende.tan@starfivetech.com/
- Avoid introducing a new function just to set the interrupt-on-completion
  bit, as it is wasteful to do so.
- Delegate the responsibility of calling dma_wmb() from main driver code
  to set_rx_owner() callbacks (i.e. let callbacks to manage the low-level
  ordering/barrier rather than cluttering up the main driver code).
v1: https://patchwork.kernel.org/project/netdevbpf/patch/20240814092438.3129-1-ende.tan@starfivetech.com/
---
 drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c   | 6 ++++--
 drivers/net/ethernet/stmicro/stmmac/dwxgmac2_descs.c | 6 ++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
index 1c5802e0d7f4..dfcbe7036988 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
@@ -186,10 +186,12 @@ static void dwmac4_set_tx_owner(struct dma_desc *p)
 
 static void dwmac4_set_rx_owner(struct dma_desc *p, int disable_rx_ic)
 {
-	p->des3 |= cpu_to_le32(RDES3_OWN | RDES3_BUFFER1_VALID_ADDR);
+	u32 flags = cpu_to_le32(RDES3_OWN | RDES3_BUFFER1_VALID_ADDR);
 
 	if (!disable_rx_ic)
-		p->des3 |= cpu_to_le32(RDES3_INT_ON_COMPLETION_EN);
+		flags |= cpu_to_le32(RDES3_INT_ON_COMPLETION_EN);
+
+	p->des3 |= flags;
 }
 
 static int dwmac4_get_tx_ls(struct dma_desc *p)
diff --git a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_descs.c b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_descs.c
index fc82862a612c..0c7ea939f787 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_descs.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_descs.c
@@ -56,10 +56,12 @@ static void dwxgmac2_set_tx_owner(struct dma_desc *p)
 
 static void dwxgmac2_set_rx_owner(struct dma_desc *p, int disable_rx_ic)
 {
-	p->des3 |= cpu_to_le32(XGMAC_RDES3_OWN);
+	u32 flags = cpu_to_le32(XGMAC_RDES3_OWN);
 
 	if (!disable_rx_ic)
-		p->des3 |= cpu_to_le32(XGMAC_RDES3_IOC);
+		 flags |= cpu_to_le32(XGMAC_RDES3_IOC);
+
+	p->des3 |= flags;
 }
 
 static int dwxgmac2_get_tx_ls(struct dma_desc *p)
-- 
2.34.1