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i.MX6 ULL eMMC has bit errors during 8 bit bus width

Question asked by lategoodbye on Feb 6, 2018
Latest reply on Feb 8, 2018 by igorpadykov


we have a custom board with i.MX6 ULL and Micron MTFC4GACAJCN-4M at usdhc2 (eMMC JEDEC 5.0) running under official FSL BSP 4.1.15-2.0.1. Using 4 bus width works perfectly in HS200 mode.


If i adjust the DTS to 8 bit bus width, i always got the following error and Linux switches back to 4 bit bus width:

mmc1: switch to bus width 2 failed


I investigated this issue and found out that mmc_compare_ext_csds() fails with error code -84 (EBADMSG). Then i dumped the EXT CSD register (dumps attached). If i compare both files i see a few bit errors in the 8 bit dump (at byte 19,157,184,196,213,214,231,241,247,487,488). These bit errors are the same over several boards (same layout).


This issue looks similiar to this, but we think the DAT lines are connected properly:

IMX6SX eMMC DDR with 8 bits bus problem 


Here are the relevant parts of the DT:

pinctrl_usdhc2_8bit: pinctrl_usdhc2_8bitGrp {
        fsl,pins = <
            MX6UL_PAD_CSI_VSYNC__USDHC2_CLK     0x10069
            MX6UL_PAD_CSI_HSYNC__USDHC2_CMD     0x17059
            MX6UL_PAD_CSI_DATA00__USDHC2_DATA0     0x17059
            MX6UL_PAD_CSI_DATA01__USDHC2_DATA1     0x17059
            MX6UL_PAD_CSI_DATA02__USDHC2_DATA2     0x17059
            MX6UL_PAD_CSI_DATA03__USDHC2_DATA3     0x17059
            MX6UL_PAD_CSI_DATA04__USDHC2_DATA4     0x17059
            MX6UL_PAD_CSI_DATA05__USDHC2_DATA5     0x17059
            MX6UL_PAD_CSI_DATA06__USDHC2_DATA6     0x17059
            MX6UL_PAD_CSI_DATA07__USDHC2_DATA7     0x17059

    pinctrl_usdhc2_8bit_100MHz: pinctrl_usdhc2_8bit_100MHz_Grp {
        fsl,pins = <
            MX6UL_PAD_CSI_VSYNC__USDHC2_CLK     0x100b9     
            MX6UL_PAD_CSI_HSYNC__USDHC2_CMD     0x170b9
            MX6UL_PAD_CSI_DATA00__USDHC2_DATA0     0x170b9
            MX6UL_PAD_CSI_DATA01__USDHC2_DATA1     0x170b9
            MX6UL_PAD_CSI_DATA02__USDHC2_DATA2     0x170b9
            MX6UL_PAD_CSI_DATA03__USDHC2_DATA3     0x170b9
            MX6UL_PAD_CSI_DATA04__USDHC2_DATA4     0x170b9
            MX6UL_PAD_CSI_DATA05__USDHC2_DATA5     0x170b9
            MX6UL_PAD_CSI_DATA06__USDHC2_DATA6     0x170b9
            MX6UL_PAD_CSI_DATA07__USDHC2_DATA7     0x170b9

    pinctrl_usdhc2_8bit_200MHz: pinctrl_usdhc2_8bit_200MHz_Grp {
        fsl,pins = <
            MX6UL_PAD_CSI_VSYNC__USDHC2_CLK     0x100f9
            MX6UL_PAD_CSI_HSYNC__USDHC2_CMD     0x170f9
            MX6UL_PAD_CSI_DATA00__USDHC2_DATA0     0x170f9
            MX6UL_PAD_CSI_DATA01__USDHC2_DATA1     0x170f9
            MX6UL_PAD_CSI_DATA02__USDHC2_DATA2     0x170f9
            MX6UL_PAD_CSI_DATA03__USDHC2_DATA3     0x170f9
            MX6UL_PAD_CSI_DATA04__USDHC2_DATA4     0x170f9
            MX6UL_PAD_CSI_DATA05__USDHC2_DATA5     0x170f9
            MX6UL_PAD_CSI_DATA06__USDHC2_DATA6     0x170f9
            MX6UL_PAD_CSI_DATA07__USDHC2_DATA7     0x170f9

&usdhc2 {
     pinctrl-names = "default", "state_100mhz", "state_200mhz";
     pinctrl-0 = <&pinctrl_usdhc2_8bit>;
     pinctrl-1 = <&pinctrl_usdhc2_8bit_100MHz>;
     pinctrl-2 = <&pinctrl_usdhc2_8bit_200MHz>;
     bus-width = <8>;
     status = "okay";


Here is the debugfs output:

# cat /sys/kernel/debug/mmc1/ios
clock: 132000000 Hz
actual clock: 132000000 Hz
vdd: 21 (3.3 ~ 3.4 V)
bus mode: 2 (push-pull)
chip select: 0 (don't care)
power mode: 2 (on)
bus width: 2 (4 bits)
timing spec: 9 (mmc HS200)
signal voltage: 0 (1.80 V)