[openwrt/openwrt] mediatek: filogic: mt7986: fix SPI driving for NAND and increase to 52MHz on ZyXEL EX5601

[LEDE Commits]

hauke pushed a commit to openwrt/openwrt.git, branch main:
https://git.openwrt.org/058bd6c9d3a058206f1b8eb9f229d5793eea1df4

commit 058bd6c9d3a058206f1b8eb9f229d5793eea1df4
Author: Sky Huang <SkyLake.Huang at mediatek.com>
AuthorDate: Fri May 16 18:45:02 2025 +0800

    mediatek: filogic: mt7986: fix SPI driving for NAND and increase to 52MHz on ZyXEL EX5601
    
    8mA driving will cause overshoot issue on SPI NAND. Change it to 4mA.
    - Reference:
    https://git01.mediatek.com/plugins/gitiles/openwrt/feeds/mtk-openwrt-feeds/+/003744197aa3a587828b4330ab1112ebdb9e840a
    
    On Linux mainline (mt7986.dtsi), spi's source clock is: clocks = <&topckgen CLK_TOP_MPLL_D2>, which is
    208MHz. Usable clock division will be:
    - 208/4=52MHz
    - 208/6~=35MHz
    - 208/8=26MHz
    and so on
    
    If we specify 50MHz for spi-max-frequency, it will actually run under about 35MHz. Most SPI NAND & NOR
    flashes are capable of running with more than 52MHz, include Micorn MT29F4G01ABAFDWB on ZyXEL EX5601.
    [Ref: #18752] To reach highest performance on mt7986, use spi-max-frequency = <520000000>. Basically,
    this setting should work on all mt7986 PCBs since most mt7986 boards follow reference design. However,
    other boards needs further test to guarantee stability.
    
    Signed-off-by: Sky Huang <SkyLake.Huang at mediatek.com>
    Tested-by: Aleksander Jan Bajkowski <olek2 at wp.pl>
    Link: https://github.com/openwrt/openwrt/pull/18813
    Signed-off-by: Hauke Mehrtens <hauke at hauke-m.de>
---
 target/linux/mediatek/dts/mt7986a-zyxel-ex5601-t0-common.dtsi | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/target/linux/mediatek/dts/mt7986a-zyxel-ex5601-t0-common.dtsi b/target/linux/mediatek/dts/mt7986a-zyxel-ex5601-t0-common.dtsi
index f714509f50..b68f386e8b 100644
--- a/target/linux/mediatek/dts/mt7986a-zyxel-ex5601-t0-common.dtsi
+++ b/target/linux/mediatek/dts/mt7986a-zyxel-ex5601-t0-common.dtsi
@@ -168,7 +168,7 @@
                 #size-cells = <1>;
                 compatible = "spi-nand";
                 reg = <1>;
-                spi-max-frequency = <50000000>;
+                spi-max-frequency = <52000000>;
                 spi-tx-bus-width = <4>;
                 spi-rx-bus-width = <4>;
 
@@ -327,12 +327,12 @@
 		};
 		conf-pu {
 			pins = "SPI2_CS", "SPI2_HOLD", "SPI2_WP";
-			drive-strength = <8>;
+			drive-strength = <4>;
 			mediatek,pull-up-adv = <0>;	/* bias-disable */
 		};
 		conf-pd {
 			pins = "SPI2_CLK", "SPI2_MOSI", "SPI2_MISO";
-			drive-strength = <8>;
+			drive-strength = <4>;
 			mediatek,pull-down-adv = <0>;	/* bias-disable */
 		};
 	};