During mass manufacturing, we noticed the mmc_rx_crc_error counter, as reported by "ethtool -S eth0 | grep mmc_rx_crc_error", to increase above zero during nuttcp speedtests. Most of the time, this did not affect the achieved speed, but it prompted this investigation.

Cycling through the rx_delay range on six boards (see table below) of various ages shows that there is a large good region from 0x12 to 0x35 where we see zero crc errors on all tested boards.

The old rx_delay value (0x10) seems to have always been on the edge for the KSZ9031RNX that is usually placed on Puma.

Choose "rx_delay = 0x23" to put us smack in the middle of the good region. This works fine as well with the KSZ9131RNX PHY that was used for a small number of boards during the COVID chip shortages.

Board S/N PHY rx_delay good region --------- --- -------------------- Puma TT0069903 KSZ9031RNX 0x11 0x35 Puma TT0157733 KSZ9031RNX 0x11 0x35 Puma TT0681551 KSZ9031RNX 0x12 0x37 Puma TT0681156 KSZ9031RNX 0x10 0x38 Puma 17496030079 KSZ9031RNX 0x10 0x37 (Puma v1.2 from 2017) Puma TT0681720 KSZ9131RNX 0x02 0x39 (alternative PHY used in very few boards)

Intersection of good regions = 0x12 0x35 Middle of good region = 0x23

Fixes: 2c66fc34e945 ("arm64: dts: rockchip: add RK3399-Q7 (Puma) SoM") Cc: stable@vger.kernel.org Reviewed-by: Quentin Schulz quentin.schulz@cherry.de Tested-by: Quentin Schulz quentin.schulz@cherry.de # Puma v2.1 and v2.3 with KSZ9031 Signed-off-by: Jakob Unterwurzacher jakob.unterwurzacher@cherry.de --- v4: drop internal Relates-to tag, add Tested-by, rebase to Linus master, send with b4 v3: use rx_delay = 0x23 instead of 0x11, which was not enough. v2: cc stable, add "Fixes:", add omitted "there" to commit msg, v1: initial submission --- arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi b/arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi index d12e661dfd9917f820284477a215389c16205f46..995b30a7aae01a0326e9f80d6be930f227968539 100644 --- a/arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi +++ b/arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi @@ -182,7 +182,7 @@ &gmac { snps,reset-active-low; snps,reset-delays-us = <0 10000 50000>; tx_delay = <0x10>; - rx_delay = <0x10>; + rx_delay = <0x23>; status = "okay"; };

--- base-commit: f932fb9b40749d1c9a539d89bb3e288c077aafe5 change-id: 20241213-puma_rx_delay-fadbcdf09783

Best regards,