[U-Boot] [linux-sunxi] Re: [PATCH 0/7] ARM: sunxi: Add basic support for Allwinner A31 (sun6i)

[Siarhei Siamashka]

On Tue, 09 Sep 2014 09:00:57 +0200
Hans de Goede <hdegoede at redhat.com> wrote:

> Hi,
> 
> On 09/08/2014 03:28 PM, Chen-Yu Tsai wrote:
> > Hi everyone,
> > 
> > This series add basic support for Allwinner's A31 SoC. The patches,
> > excluding the first one, were cherry-picked from u-boot-sunxi. Due to
> > the difference between u-boot mainline and u-boot-sunxi, some patches
> > were rearranged or squashed to better fit the current state of u-boot,
> > and not introduce any build breaks. It follows Ian's initial merge
> > method of sun7i support: introducing various components first, then
> > enabling them in the last commit. I tried to keep the commits separate,
> > thus retaining the original author and Signed-off-bys.
> > 
> > Patch 1 adds a wrapper around "func(USB, usb, 0)" in BOOT_TARGET_DEVICES
> > to deal with breakage when USB support is not enabled.
> > 
> > Patch 2 adds memory addresses for some hardware blocks new in sun6i.
> > 
> > Patch 3 adds support for the new PRCM (power reset and clock management)
> > block, which also contains PLL bias voltage control.
> > 
> > Patch 4 adds support for the clock module. This patch is a bunch of
> > different sun6i related patches on the clock code, from when sun6i
> > support was introduced to u-boot-sunxi, up to its current form.
> > This is done to avoid various conflicts and needlessly introducing
> > then removing macros.
> > 
> > Patch 5 adds mmc support on sun6i.
> > 
> > Patch 6 adds uart0 muxing on sun6i.
> > 
> > Patch 7 enables sun6i support and adds defconfig for the Colombus board.
> 
> Chen,
> 
> Many thanks for working on this!
> 
> Just a quick not for people celebrating too early, this is the *incomplete*
> sun7i support from the linux-sunxi/u-boot-sunxi git repo. It is fine to
> merge this upstream, but this does not include SPL support.
> 
> This allows replacing u-boot.bin on allwinnner sd-card images, which is
> very useful. But it does not get us all the way to booting sun7i devices
> we still need boot0 and boot1 binaries from allwinner for that (for now).

If I understand it correctly, one of the things that needs to be done
in SPL is the initialization of the DRAM controller. A few weeks ago
Oliver has updated the http://linux-sunxi.org/DRAM_Controller page
and added a link to the 'dram_sun6i.c' file from the rhombus-tech.net
u-boot repository:
    http://git.rhombus-tech.net/?p=u-boot.git;a=blob;f=arch/arm/cpu/armv7/sunxi/dram_sun6i.c;hb=refs/heads/allwinner-sunxi-a31
Does this repository look like exactly the missing part of code?
Assuming that this code works, it provides a usable starting point
for us.

It looks like the Allwinner A31 DRAM controller registers are very
similar to what is used in RK3288 (I have not checked the details,
but if we are very lucky, it might be even a 100% perfect match):
    https://chromium-review.googlesource.com/#/c/209419/
And thanks to the Rockchip developers (who are contributing this
DRAM controller support code to coreboot), now we have a lot of
named defines for the individual bitfields in the hardware
registers. So we can decode the magic constants used in the
Allwinner code. And thanks to Texas Instruments, we also have
some useful documentation, which also happens to be a reasonably
good match:
    http://www.ti.com/lit/ug/spruhn7a/spruhn7a.pdf

In general, if we are on our own, then we just need to do all the
boring work again (similar to what we did with the Allwinner
A10/A13/A20 DRAM controller earlier). Starting with the creation of the
    http://linux-sunxi.org/A31_DRAM_Controller_Register_Guide
wiki page and populating it with the information gathered from the
Allwinner and Rockchip source code and also from the TI Keystone2
documentation. Naturally, every bit of this information needs to
be verified on real Allwinner A31 hardware before we can make any
assumptions.

However Allwinner has promised to provide us with some better
documentation later this month:
    https://www.mail-archive.com/linux-sunxi@googlegroups.com/msg06840.html
I don't know if they are going to include the documentation for the
DRAM controller in the first new documentation delivery. It surely
may be complicated, because Allwinner is obviously licensing the DRAM
controller IP from a third party and not designing it from scratch
(in a nice company with Rockchip and Texas Instruments). But Texas
Instruments somehow can provide the DRAM controller documentation
in free public access. So I would guess that it should be possible
for Allwinner too.

We still need proper Power-Down and Self-Refresh mode support for
Allwinner A10/A13/A20. And I had plans to do some investigation for
this stuff. But now this activity is temporarily suspended until
we see what kind of assistance Allwinner is going to provide to us
(A usable DRAM controller documentation? A contribution of DRAM
code for u-boot? Nothing?).

-- 
Best regards,
Siarhei Siamashka