[U-Boot] [PATCH v9 2/2] Odroid-XU3: Add documentation for Odroid-XU3

[Kevin Hilman <khilman@kernel.org>]

Lukasz Majewski <l.majewski@majess.pl> writes:

[...]

>> On 28 November 2014 at 06:46, Lukasz Majewski <l.majewski@majess.pl>
>> wrote:
>> > Hello Javier,
>> >
>> >> Hello Lukasz,
>> >>
>> >> On Fri, Nov 28, 2014 at 9:39 AM, Lukasz Majewski
>> >> <l.majewski@majess.pl> wrote:
>> >> >> I have yet to take him up on that offer though, but it sounds
>> >> >> like a good way forward. The current layout really isn't
>> >> >> practical.
>> >> >>
>> >> >
>> >> > It indeed isn't very practical, but this is what you received
>> >> > from HardKernel when you buy XU3 board.
>> >> >
>> >> > Of course you can grab their sources, modify the layout, prepare
>> >> > u-boot's SPL and send it to them to be signed.
>> >> > However, it is not the way the "normal" user do things.
>> >> >
>> >> > He or she would like to replace standard (and outdated)
>> >> > HardKernel u-boot on their SD card and go forward with booting
>> >> > kernel.
>> >> >
>> >>
>> >> I agree with Sjoed that normal users don't replace the low-level
>> >> components that are provided by the board vendor.
>> >>
>> >> After all you can boot a mainline kernel using the vendor u-boot,
>> >> just append the DTB and create a uImage. The practical reason why
>> >> someone would want to replace the vendor u-boot is to have more
>> >> features but is very hard to do if there is a constraint in the
>> >> maximum u-boot image size (even harder if the maximum is such
>> >> small like in the XU3).
>> >
>> > I agree that 328 KiB size for u-boot is a constraint. I don't know
>> > HardKernel's justification for this.
>> >
>> >>
>> >> > For now we _must_ focus on supporting XU3 with default BL1/BL2
>> >> > and hence we are obliged to have u-boot size smaller than 328
>> >> > KiB.
>> >> >
>> >> > It is challenging but for sure doable.
>> >> >
>> >>
>> >> It is doable but I don't see why the default BL2 _must_ be used.
>> >
>> > For practical/pragmatic reasons:
>> >
>> > 1. It is difficult to have signed BL2 - each time we need to ask
>> > HardKernel for signing it. It is impractical and hampers usage of
>> > mainline SPL (BL2) with XU3.
>> >
>> > 2. All the documentation on the HardKernel wiki site refers to the
>> > default BL2.
>> >
>> > 3. We will have "new" BL2, which source code is based on 2012.07
>> > mainline u-boot.
>> >
>> > 4. Two BL2 binaries - IMHO will hurt (i.e. brick) some device sooner
>> > or latter.
>> >
>> >>
>> >> A user that wants to replace the kernel or u-boot is already
>> >> tech-savy and can for sure replace the BL2 as well if it's
>> >> publicly available.
>> >
>> > Sorry, but I'm a bit sceptical about updating such low level code.
>> > Bad things do happen.
>> >
>> >> Maybe hardkernel folks can even make the modified BL2 available on
>> >> their website and the link added in the comment explaining the
>> >> layout?
>> >
>> > We would then require HardKernel to:
>> >
>> > 1. Provide updated BL2.img
>> > 2. Update their wiki to reflect the new BL2.
>> >
>> >>
>> >> Also, it is an artificial constraint after all and can be easily
>> >> modified. In fact I think we should push hardkernel to change that
>> >> layout by default and use a BL2/SPL that has more sensible size for
>> >> the u-boot binary even if they don't need it for their vendor
>> >> u-boot which seems to be quite small.
>> >
>> > I totally agree.
>> >
>> > I'd like to propose a following plan:
>> >
>> > 1. Accept Hyungwon's patches to have XU3 u-boot < 328 KiB (with
>> > link to default BL2) to have XU3 support in place (and treat it as
>> > a starting point)
>> >
>> > 2. If u-boot's size less than 328 KiB is _really_ a problem to
>> > somebody then ask hardkernel to change BL2 or:
>> >         - modify their sources to change the layout (I regard this
>> > as a "quick hack" solution)
>> >         - with a lot of pain develop BL2/SPL (by whom?) which base
>> > on newest mainline (then for each test hardkernel must sign the
>> >           binary).
>> 
>> My 2p worth...
>> 
>> The current Hardkernel BL1 looks broken to me - it is just too old.
>
> +1
>

FWIW, the XU3 firmware is broken in other ways as well which have a
major impact on power management.  

First, with mainline kernels using MCPM, only 6 of 8 CPUs come
online.  However, even with that fixed[1], it turns out that the kernel
can't properly manage CCI due to secure firmware[2], which means that MCPM
(multi-cluster power management) can't work, and thus the low-power
cluster-idle states can't work, the big.LITTLE switcher cannot work, and
the ongoing work on energy-aware scheduling will not be useful on this
platform.

Anyone know what are the chances of getting a non-secure version of the
firmware for this platform.  The Samsung Chromebook2 with basically the
same SoC (5800 compared to the 5422 on the XU3) ships with non-secure
firmware so all of the above mentioned features are working just fine.

I'm working on getting these same features working on the XU3, but this
broken firmware as brought a halt to any real progress.

Kevin

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/305790.html
[2] http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/306480.html