[U-Boot] [linux-sunxi] [UBOOT] Both Linux-Sunxi and Mainline Uboot have issues

[Hans de Goede]

Hi,

On 19-02-15 07:29, TsvetanUsunov wrote:
> Hi
>
> For A13-OLinuxino till now we conservatively used the Linux-Sunxi uboot,
> but we recently got new lot of Samsung memories and we decided to tweak
> some parameters for this DDR in Linux-Sunxi uboot and found problems.
> As this uboot is with status not maintained anymore I will not discuss the
> problems, as probably no one will spend time on it, so we wisely decided to
> move to mainline uboot :) but it seems there are other issues to address.

First of all let me say that it is a good decision to move to upstream u-boot,
as one of the upstream u-boot Allwinner support maintainers I believe that
that is a very good decision.

In case you've not noticed yet upstream u-boot will give you a console on
hdmi (or lcd if configured in the configs/A*-OLinuxIno*_defconfig file)
and supports usb keyboards, so you can interact with u-boot without needing
to hook up a serial console, and it supports booting from sata disks, and ...
lets just say it is much better :)

> The PLL5 and PLL6 values are changed and this cause problems, this is what
> we found so far:
>
>
> 1. mainline u-boot
> =================
> 1.1 pll5
> address 0x01c20020, value 0xb1049091 - P=1, N=16, K=2, M=2.
>   The PLL5 output for DDR = (24MHz*N*K)/M. DDR=24*16*2/2 = 384MHz
> The PLL5 output for other module = (24MHz*N*K)/P. DDR=24*16*2/1 = 768MHz  -
> This high frequency cause LCDs connected to the board to flicker

pll5's clock was doubled in upstream u-boot to give downstream users
more flexibility in which clocks they can get by dividing it.

Unfortunately the allwinner derived linux-sunxi kernels have some hardcoded
assumptions about pll5 speed left and right, so you must make sure that
your kernel has these 2 commits:

https://github.com/linux-sunxi/linux-sunxi/commit/9a1cd034181af628d4145202289e1993c1687db6
https://github.com/linux-sunxi/linux-sunxi/commit/ade08aa6e5249a9e75a97393e86c250b2bcb3ec8

Alternatively you can enable the old kernel compat option in u-boot's config, so
you would do the following:

make -j4 CROSS_COMPILE=arm-linux-gnu- A13-OLinuXino_defconfig
make -j4 CROSS_COMPILE=arm-linux-gnu- menuconfig
  -> goto "ARM architecture" -> select "Enable workarounds for booting old kernels"
  -> exit -> exit -> save
make -j4 CROSS_COMPILE=arm-linux-gnu- spl/menuconfig
  Do the same as for the normal menuconfig

This will remove the doubling of the PLL5 speed.

Note assuming you're using linux-sunxi kernels and not upstream kernels you also
need "Enable workarounds for booting old kernels" for things to boot at all
on A20 based devices, because the new u-boot by default boots the kernel in
non secure mode (so that it can be a hypervisor and hw accelerated qemu-kvm works
on the A20), but the old kernels do not work when booted in non secure mode
(another bug in the old kernels, for which no fix is available).

> 1.2 pll6
> address 0x01c20028, value 0xA1009900 - N=25, K=1, M=1
>   The PLL6 output is (24MHz*N*K)/M/2 = 24*25*1/1/2 = 300MHz

Actually with upstream u-boot the value is 0xA1009911, but the end
result is the same: 24*25*2/2/2 = 300MHz

> 1.3 MBUS clock
> address 0x01c2015c, value 0x81000001  - MBUS clock source is PLL6/2 = 300/2
> = 150MHz - This is connected to PLL6 setup, at this 150 Mhz the board cant
> play video smoothly and sometimes drop video packets when the video is
> playing

Hmm, interesting so it seems that PLL6 is different on the A13 compared to
the A10/A20 and both upstream u-boot and the kernel get this wrong, and
miss the extra /2 which is being done on the A13 only, causing this.

I'll work on a fix for this and get back to you.

Regards,

Hans



>   2. sunxi u-boot
> =================
> 1.1 pll5
> address 0x01c20020, value 0xb1049091 - P=2, N=17, K=2, M=2.
>   The PLL5 output for DDR = (24MHz*N*K)/M. DDR=24*17*2/2 = 408MHz
> The PLL5 output for other module = (24MHz*N*K)/P. DDR=24*16*2/2 = 408MHz  -
> this frequency was OK, There is no problem with LCD flickering, why the
> frequency increase was necessary?
> 1.2 pll6
> address 0x01c20028, value 0xA1009900 - N=25, K=1, M=1
>   The PLL6 output is (24MHz*N*K)/M/2 = 24*25*1/1/2 = 300MHz
> 1.3 about MBUS clock
> address 0x01c2015c, value 0x82000001  - MBUS clock source is PLL5/2 = 408/2
> = 204MHz - at this frequency No packet drop when the video is playing
>
>
> Can you tell me the reasons for the PLL5 and PLL6 frequency changes to
> mainline uboot?
>
> Best regards
> Tsvetan
>