MMC2 Linux Device Tree Configuration For SD CARD on ARM PART ii

• This blog entry is useful for ARM microprocessors running Kernel versions 4.4.16-ti-rt and newer. 
• For configuring mmc2 on earlier kernel versions go to part I of this topic: 
• MMC2 Linux Device Tree Configuration For ARM PART i

What has changed since earlier kernel releases?

• There has been a recent changes (end of last year) to the dt bindings for eDMA3.  Older kernels used DEPRECATED binding for DTS files.  The old bindings were ti,edma3-tpcc/ti,edma3-tptc.  And to get mmc2 (labeled mmc3 in dts files) to work properly you must use the ti,edma-xbar-event-map property for edma:

&mmc3 {
      vmmc-supply = <&vmmcsd_fixed>;
      ti,dual-volt;
      ti,needs-special-reset;
      ti,needs-special-hs-handling;
      pinctrl-names = "default";
      pinctrl-0 = <&mmc3_pins>;
      cd-gpios = <&gpio0 31 GPIO_ACTIVE_HIGH>;
      cd-inverted;
      bus-width = <4>;
      max-frequency = <25000000>;
      dmas = <&edma 12
              &edma 13>;
      dma-names = "tx", "rx";
      status = "okay";
};

&edma {
 ti,edma-xbar-event-map = /bits/ 16 <1 12 
                                     2 13>;

};

What are the new dt bindings for eDMA3?

• "ti,edma3-tpcc" for the channel controller(s)
• "ti,edma3-tptc" for the transfer controller(s)
• "ti,am335x-edma-crossbar" for Crossbar event to channel map

The changes to mmc3 configuration is in bold below:

&mmc3 {

      vmmc-supply = <&vmmcsd_fixed>;
      ti,dual-volt;
      ti,needs-special-reset;
      ti,needs-special-hs-handling;
      pinctrl-names = "default";
      pinctrl-0 = <&mmc3_pins>;
      cd-gpios = <&gpio3 16 GPIO_ACTIVE_LOW>;
      bus-width = <4>;
      max-frequency = <25000000>;

     dmas = <&edma_xbar 12 0 1
             &edma_xbar 13 0 2>;

     #address-cells = <1>;
     #size-cells = <0>;
     dma-names = "tx", "rx";
     status = "okay";
};

• This is assuming that the pinmux configuration for mmc3 (&mmc3_pins) is:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

mmc3_pins: pinmux_mmc3_pins { pinctrl-single,pins = < /* gpmc_a1.mmc2_dat0, INPUT_PULLUP | MODE3 */ 0x44 (PIN_INPUT_PULLUP | MUX_MODE3) /* gpmc_a2.mmc2_dat1, INPUT_PULLUP | MODE3 */ 0x48 (PIN_INPUT_PULLUP | MUX_MODE3) /* gpmc_a3.mmc2_dat2, INPUT_PULLUP | MODE3 */ 0x4C (PIN_INPUT_PULLUP | MUX_MODE3) /* gpmc_ben1.mmc2_dat3, INPUT_PULLUP | MODE3 */ 0x78 (PIN_INPUT_PULLUP | MUX_MODE3) /* gpmc_csn3.mmc2_cmd, INPUT_PULLUP | MODE3 */ 0x88 (PIN_INPUT_PULLUP | MUX_MODE3) /* gpmc_clk.mmc2_clk, INPUT_PULLUP | MODE3 */ 0x8C (PIN_INPUT_PULLUP | MUX_MODE3) /* gpmc_a0.gpio1_16 */ 0x40 (PIN_OUTPUT_PULLDOWN | MUX_MODE7) /* mmc2_sdcd, p9_13, Note: Dont know why but we set card detect pinout to be GPIO */ 0x74 (PIN_INPUT_PULLDOWN | MUX_MODE7) /* mmc2_sdwp, p9_17, Note: Write protect is not configured in the device tree settings*/ 0x15c (PIN_INPUT_PULLDOWN | MUX_MODE1) >; };