[Librem-5-dev] U-Boot support for uSD

Andy Green andy at warmcat.com
Thu Dec 27 02:17:49 PST 2018

On 27/12/2018 15:09, Andy Green via Librem-5-dev wrote:
> Hi -
> It seems my reasonably midrange for 2018 uSD (Sandisk Ultra U1 32GB) 
> cannot be brought up by U-Boot on the dev board.
>   u-boot=> mmc dev 1
>   Card did not respond to voltage select!
>   mmc_init: -95, time 29
> But there's no evident problem using that card on a Linux box via a 
> cheapo USB adapter.
> "Just me"?  Known issue not on the list of known issues[1]?  Any 
> recommended cards that do work?

I retried using an ancient Class 10 non-U1 device and then with no 
device in... all the same.

Digging around in the schematics [1] it looks like mmc1 is actually the 
sdio connection to the WLAN module.  Linux says this:

[    0.486566] mmc1: SDHCI controller on 30b50000.usdhc [30b50000.usdhc] 
using ADMA
[    0.514651] mmc1: new high speed SDIO card at address fffd

The actual uSD is connected via an MA8627 [2] which is a USB hub + mmc / 
sd adapter.  The hub part appears in Linux as

Bus 001 Device 002: ID 14cd:8601 Super Top

However the other two logical devices seem to be spoken for, the WAN 
module and the interface to the SIM card it seems.

Bus 001 Device 005: ID 1e0e:9001 Qualcomm / Option
Bus 001 Device 004: ID 0424:1104 Standard Microsystems Corp.

If you stick a uSD card in though, there dynamically appears also

Bus 001 Device 005: ID 14cd:8170 Super Top

which is the mass storage device connection to the uSD card.  And 
/dev/sda* appears in Linux.

Back in U-Boot, armed with this new knowledge: no joy

u-boot=> usb start
starting USB...
No controllers found

I intended to put a newly-built kernel on uSD and have U-Boot boot from 
it to test it, but it's not supported until U-Boot supports the USB 
controller so it seems.  [4] discusses various update scenarios (mainly 
whole-image) but not this kind of thing.

I'll try putting my kernel pieces on eMMC with different names and have 
U-Boot boot from there by hand to get the same effect.


[1] https://source.puri.sm/Librem5/dvk-mx8m-bsb/blob/master/dvk-mx8m-bsb.pdf
[2] http://www.prolific.com.tw/ShowProductPDF.aspx?p_id=347
[4] https://source.puri.sm/Librem5/librem5-devkit-tools

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