[PATCH net-next] net: stmmac: dwc-qos-eth: simplify switch() in dwc_eth_dwmac_config_dt()

[PATCH net-next] net: stmmac: dwc-qos-eth: simplify switch() in dwc_eth_dwmac_config_dt()

[Russell King (Oracle)]

Simplify the 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%.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---
 .../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

Re: [PATCH net-next] net: stmmac: dwc-qos-eth: simplify switch() in dwc_eth_dwmac_config_dt()

[Maxime Chevallier]

On 18/11/2025 12:18, Russell King (Oracle) wrote:
> Simplify the 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%.
> 
> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

Maxime

> ---
>  .../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;

Re: [PATCH net-next] net: stmmac: dwc-qos-eth: simplify switch() in dwc_eth_dwmac_config_dt()

[Russell King (Oracle)]

On Tue, Nov 18, 2025 at 11:18:01AM +0000, Russell King (Oracle) wrote:
> Simplify the the switch() statement in dwc_eth_dwmac_config_dt().

I notice that "the the" stammer has appeared in this patch commit
description, which is flagged as a warning in patchwork, so I'll
re-send with that fixed.

As I have a number of other patches that depend on this, all centred
around the axi_blen stuff, I'll send this patch as part of that series.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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