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Registered: ‎02-29-2016

Need to pull eMMC RST_N low to boot

I am working on bringing up a custom board that has an eMMC module hooked up to SDHC1 on a Zynq-7000, with the RST_N line (with pull-up) going to MIO0.  There is neither a mux or conf pinctl entry for this pin/group in the devicetree.


When in u-boot I am able to “ls mmc 0:1” and see the contents of the filesystem.  When I try to boot into linux I get a "Waiting for root device /dev/mmcblk0p1...".


During my troubleshooting I found that If, in u-boot, I do a "gpio clear 0" (drive the pin low) it boots fine. What the heck!?


Other measures I have taked:

Made sure to enable RST_N in the ECSD register with the “mmc” tool - No change

Verified with an oscilloscope that the RST_N pin defaults to high, and only goes low when doing the gpio command from u-boot.

Tried adding pinctl entries into the devicetree to set the pin - this usually prevents the board from booting no matter what I do with the reset line in uboot.


Any advice would be greatly appreciated - I am quickly running out of ideas to try.


- Sam

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