[U-Boot] [PATCH] rockchip: rk3399-puma: reduce sd card max-frequency to 40MHz

[Philipp Tomsich]

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 at theobroma-systems.com>
Signed-off-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
Tested-by: Christoph Muellner <christoph.muellner at theobroma-systems.com>
---

 arch/arm/dts/rk3399-puma.dtsi | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/dts/rk3399-puma.dtsi b/arch/arm/dts/rk3399-puma.dtsi
index 261df42..ba9bb4c 100644
--- a/arch/arm/dts/rk3399-puma.dtsi
+++ b/arch/arm/dts/rk3399-puma.dtsi
@@ -505,7 +505,7 @@
 &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;
-- 
2.1.4