rockchip: rk3399-puma: reduce sd card max-frequency to 40MHz

Some SanDisk Ultra cards trigger intermittent errors on detection
resulting in an -EOPNOTSUPP, when running at 50MHz.

Waveform analysis suggest that the level shifters that are used on the
RK3399-Q7 module (for voltage translation between the on-module
voltages and the 3.3V required on the card-edge) don't handle clock
rates at or above 48MHz properly. This change reduces the maximum
frequency on the external SD-interface to 40MHz (for a safety margin
of 20%).

Reported-by: Jakob Unterwurzacher <jakob.unterwurzacher@theobroma-systems.com>
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Tested-by: Christoph Muellner <christoph.muellner@theobroma-systems.com>

diff --git a/arch/arm/dts/rk3399-puma.dtsi b/arch/arm/dts/rk3399-puma.dtsi
index 6e7e1e3..11ffcb7 100644 (file)
--- a/arch/arm/dts/rk3399-puma.dtsi
+++ b/arch/arm/dts/rk3399-puma.dtsi
@@ -503,7 +503,7 @@
 &sdmmc {
        u-boot,dm-pre-reloc;
        clock-frequency = <150000000>;
-       clock-freq-min-max = <100000 150000000>;
+       max-frequency = <40000000>;
        supports-sd;
        bus-width = <4>;
        cap-mmc-highspeed;