[U-Boot] [bug report] sunxi: booting from eMMC

[Maxime Ripard]

Hi,

On Mon, Sep 12, 2016 at 04:47:49PM +0200, Hans de Goede wrote:
> On 12-09-16 15:56, Maxime Ripard wrote:
> >Hi,
> >
> >On Mon, Sep 12, 2016 at 01:53:24PM +0200, Ciprian Manea wrote:
> >>I'm using a SinA33 dev board (Allwinner a33 SoC) and at the moment
> >>I'm trying to boot from the eMMC.
> >>
> >>But it fails in the following way:
> >>
> >>
> >>*Got the following error at boot time:*
> >>*U-Boot SPL 2016.09-rc2-00125-g6e8b42f (Sep 08 2016 - 11:00:46) DRAM: 1024
> >>MiB Trying to boot from MMC2 MMC Device 1 not found spl: could not find mmc
> >>device. error: -19 SPL: failed to boot from all boot devices ### ERROR ###
> >>Please RESET the board ###*
> >
> >So I've been on the same issue for the last couple of days.
> >
> >Since that board is already supported, adding support for the eMMC
> >basically came down to that patch on top of 2016.09-rc2.
> >
> >http://code.bulix.org/kcgxri-106037?raw
> >
> >(Quite hackish, the 8-Bits part being a separate issue that would need
> >to be addressed somehow).
> >
> >However, it doesn't work, neither when flashing u-boot on the eMMC
> >itself (where there's a timeout error in the SPL) nor when trying to
> >access the eMMC from a U-Boot loaded from the (external) SD.
> >
> >In the latter case, even mmc dev 1 fails silently.
> >
> >I traced that down to the mmc_switch here:
> >http://git.denx.de/?p=u-boot.git;a=blob;f=drivers/mmc/mmc.c#l530
> >
> >Which fails with ETIMEDOUT, and more specifically, it's the call to
> >mmc_rint_wait here
> >http://git.denx.de/?p=u-boot.git;a=blob;f=drivers/mmc/sunxi_mmc.c#l383
> >that times out.
> >
> >Increasing the timeout value (to 10000) doesn't really change
> >anything. I guess this is also the reason why we had a timeout error
> >in the SPL.
> >
> >This eMMC works fine in Linux, with the same muxing (and I guess the
> >earlier commands wouldn't be successful if the muxing or power was not
> >set up appropriately). So I'm kind of running out of ideas on what
> >could be the root cause of this.
> >
> >Hans, any ideas?
> 
> Maybe the emmc needs external pull-ups ? I don't remember if u-boot
> always enables those or not ...

So I pushed this a bit more, and it seems like commenting the call to
mmc_change_freq makes everything just work.

Reading the JEDEC spec, it looks like when you switch to high speed,
you also need to change the controller clock rate, that u-boot doesn't
seem to do at the moment, which obviously will fail, since the
controller will be stuck at the former rate, while the eMMC would be
switched.

If I comment mmc_change_freq, everything works.

> I've not tried booting from eMMC on A33 boards (-ENOHARDWARE) but it
> does work on A13 and A20 boards (last time I tried).

I'm guessing this is more about what rates and modes are supported,
rather than the actual SoC.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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