AM5728: SD UHS support in U-boot

Part Number: AM5728

platform : am572x-idk

sdk : processor-sdk-linux 05.02.00.10

U-Boot version: 2018.01

U-Boot config: am57xx_evm_defconfig

U-Boot devicetree: am572x-idk.dts 

Here is the part of the device tree related to mmc1:

&mmc1 {
pinctrl-names = "default", "hs", "sdr12", "sdr25", "sdr50", "ddr50", "sdr104";
pinctrl-0 = <&mmc1_pins_default>;
pinctrl-1 = <&mmc1_pins_hs>;
pinctrl-2 = <&mmc1_pins_sdr12>;
pinctrl-3 = <&mmc1_pins_sdr25>;
pinctrl-4 = <&mmc1_pins_sdr50>;
pinctrl-5 = <&mmc1_pins_ddr50 &mmc1_iodelay_ddr_rev20_conf>;
pinctrl-6 = <&mmc1_pins_sdr104 &mmc1_iodelay_sdr104_rev20_conf>;
};

&mmc1 {
status = "okay";
vmmc-supply = <&v3_3d>;
vqmmc-supply = <&ldo1_reg>;
bus-width = <4>;
cd-gpios = <&gpio6 27 GPIO_ACTIVE_LOW>; /* gpio 219 */
};

v3_3d: fixedregulator-v3_3d {
compatible = "regulator-fixed";
regulator-name = "V3_3D";
vin-supply = <&smps9_reg>;
regulator-min-microvolt = <3300000>;
regulator-max-microvolt = <3300000>;
regulator-always-on;
regulator-boot-on;
};

&i2c1 {
@tps659038 {
tps659038_pmic {
regulators {
smps9_reg: smps9 {

/* VDD_3_3D */
regulator-name = "smps9";
regulator-min-microvolt = <3300000>;
regulator-max-microvolt = <3300000>;
regulator-always-on;
regulator-boot-on;
};

ldo1_reg: ldo1 {
/* VDDSHV8 - VSDMMC */
/* NOTE: on rev 1.3a, data supply */
regulator-name = "ldo1";
regulator-min-microvolt = <1800000>;
regulator-max-microvolt = <3300000>;
regulator-boot-on;
regulator-always-on;
};
};
};
};
};

I am using a SanDisk Extreme® microSDXC™ UHS-I CARD：https://shop.westerndigital.com/products/memory-cards/sandisk-extreme-uhs-i-microsd#SDSQXA2-064G-AN6MA

I want to support UHS mode in uboot, but it seems to be unsuccessful. Debugging found that UHS capabilities was masked in the sd_select_mode_and_width function:Image may be NSFW.
Clik here to view.

uhs_en depends on bit [24] (OCR_S18R) of mmc->ocr, which is set in function sd_send_op_cond:

Send CMD55 and ACMD41, then (OCR) content in the response on the CMD line.

Image may be NSFW.
Clik here to view.

#define MMC_CMD_APP_CMD 55

#define SD_CMD_APP_SEND_OP_COND 41

#define OCR_BUSY 0x80000000

#define OCR_HCS 0x40000000

#define OCR_S18R 0x1000000

Image may be NSFW.
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Image may be NSFW.
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I added some print information to these two functions, and found that bit [24] (OCR_S18R) of cmd.arg is 1, but bit [24] (OCR_S18R) of cmd.response[0] is 0.

Image may be NSFW.
Clik here to view.

Then I look at the OCR register definition, bit [24-30] is reserved.

Image may be NSFW.
Clik here to view.[

1. I want to know what is the definition of bit [24] of ocr? Why use it as a flag to UHS?

2. The print information contains this error "mmc@4809c000: No vmmc supply" in function mmc_power_init. Vmmc supply was set but not found. Why is that? Does it affect uhs mode?