netdev - [PATCH net-next 1/6] net: stmmac: dwc-qos-eth: simplify switch() in dwc_eth_dwmac_config

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Message-Id: <E1vLfLG-0000000FMai-3fKz@rmk-PC.armlinux.org.uk>
Date: Wed, 19 Nov 2025 10:23:14 +0000
From: "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>
Cc: Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-stm32@...md-mailman.stormreply.com,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>
Subject: [PATCH net-next 1/6] net: stmmac: dwc-qos-eth: simplify switch() in
 dwc_eth_dwmac_config_dt()

Simplify the switch() statement in dwc_eth_dwmac_config_dt().
Although this is not speed-critical, simplifying it can make it more
readable. This also drastically improves the code emitted by the
compiler.

On aarch64, with the original code, the compiler loads registers with
every possible value, and then has a tree of test-and-branch statements
to work out which register to store. With the simplified code, the
compiler can load a register with '4' and shift it appropriately.

This shrinks the text size on aarch64 from 4289 bytes to 4153 bytes,
a reduction of 3%.

Reviewed-by: Maxime Chevallier <maxime.chevallier@...tlin.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
--
v2: remove "the the" in commit description
---
 .../stmicro/stmmac/dwmac-dwc-qos-eth.c        | 26 +++----------------
 1 file changed, 3 insertions(+), 23 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-dwc-qos-eth.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-dwc-qos-eth.c
index c7cd6497d42d..e6d5893c5905 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-dwc-qos-eth.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-dwc-qos-eth.c
@@ -84,29 +84,9 @@ static int dwc_eth_dwmac_config_dt(struct platform_device *pdev,
 	device_property_read_u32(dev, "snps,burst-map", &burst_map);
 
 	/* converts burst-map bitmask to burst array */
-	for (bit_index = 0; bit_index < 7; bit_index++) {
-		if (burst_map & (1 << bit_index)) {
-			switch (bit_index) {
-			case 0:
-			plat_dat->axi->axi_blen[a_index] = 4; break;
-			case 1:
-			plat_dat->axi->axi_blen[a_index] = 8; break;
-			case 2:
-			plat_dat->axi->axi_blen[a_index] = 16; break;
-			case 3:
-			plat_dat->axi->axi_blen[a_index] = 32; break;
-			case 4:
-			plat_dat->axi->axi_blen[a_index] = 64; break;
-			case 5:
-			plat_dat->axi->axi_blen[a_index] = 128; break;
-			case 6:
-			plat_dat->axi->axi_blen[a_index] = 256; break;
-			default:
-			break;
-			}
-			a_index++;
-		}
-	}
+	for (bit_index = 0; bit_index < 7; bit_index++)
+		if (burst_map & (1 << bit_index))
+			plat_dat->axi->axi_blen[a_index++] = 4 << bit_index;
 
 	/* dwc-qos needs GMAC4, AAL, TSO and PMT */
 	plat_dat->core_type = DWMAC_CORE_GMAC4;
-- 
2.47.3