Linux: AM5728 MMC clock

Babji,

"max-frequency" of mmc3 is set in file dra7.dtsi, it is set to 64MHz and I suggest you to not change that value.

mmc3: mmc@480ad000 {
            compatible = "ti,dra7-hsmmc", "ti,omap4-hsmmc";
            reg = <0x480ad000 0x400>;
            interrupts = <GIC_SPI 89 IRQ_TYPE_LEVEL_HIGH>;
            ti,hwmods = "mmc3";
            ti,needs-special-reset;
            dmas = <&sdma_xbar 77>, <&sdma_xbar 78>;
            dma-names = "tx", "rx";
            status = "disabled";
            /* Errata i887 limits max-frequency of MMC3 to 64 MHz */
            max-frequency = <64000000>;
            sd-uhs-sdr12;
            sd-uhs-sdr25;
            sd-uhs-sdr50;
        };

Babji Pakala said:

But, when checked the clock frequency with oscilloscope, I am getting around 25 MHz only.

Most probably you are in mode sd-uhs-sdr12 (24MHz) and you need to switch to mode sd-uhs-sdr25 (48MHz). You can do that in am57xx-evm-common.dtsi file, try the below approach:

&mmc3 {
    status = "okay";
    vmmc-supply = <&vmmcwl_fixed>;
    bus-width = <4>;
    pinctrl-names = "default";
    cap-power-off-card;
    keep-power-in-suspend;
    ti,non-removable;
    +/delete-property/ sd-uhs-sdr12;
    +/delete-property/ sd-uhs-sdr50;

    #address-cells = <1>;
    #size-cells = <0>;
    wlcore: wlcore@2 {
        compatible = "ti,wl1835";
        reg = <2>;
        interrupt-parent = <&gpio5>;
        interrupts = <7 IRQ_TYPE_LEVEL_HIGH>;
    };
};

Then you can trace the flow in linux-kernel/drivers/mmc/core/host.c file and verify that MMC_CAP_UHS_SDR25 is set for host->caps.

Note also that the external WiFi module should also support SDR25 mode (48MHz, 24Mbps).

Regards,
Pavel

If you look in the Silicon Errata, you'll see the speed limits on each mmc. MMC3 has a maximum speed of 64MHz.

Steve K.