Subject: "ARM: multi_v7_defconfig: Enable shmobile platforms" breaks Tegra20 multi_v7_defconfig boot

From: [email-masked] (Stephen Warren)
Date: Wed, 01 Apr 2015 12:55:33 -0600

(Dropping people likely not interested in Tegra U-Boot from explicit Cc)

On 04/01/2015 11:48 AM, Paul Walmsley wrote:
> On 04/01/2015 11:14 AM, Stephen Warren wrote:
>> On 03/26/2015 12:57 PM, Stephen Warren wrote:
>>> On 03/26/2015 12:35 PM, Paul Walmsley wrote:
>>>> On Wed, 25 Mar 2015, Stephen Warren wrote:
>>>>
>>>>> On 03/25/2015 04:00 PM, Paul Walmsley wrote:
>>>>>> On Wed, 25 Mar 2015, Tyler Baker wrote:
>>>>>>> On 25 March 2015 at 11:03, Paul Walmsley <[email-masked]> wrote:
>>>>>>>> Looks like commit 4a3a6f86693922b29cf829c63f652b057f14619e ("ARM:
>>>>>>>> multi_v7_defconfig: Enable shmobile platforms") breaks Tegra20
>>>>>>>> multi_v7_defconfig boot.
>> ...
>>>>>>> Can you try to shift your kernel load address around a bit? From
>>>>>>> experience with the boards from kernelci.org we find that as the
>>>>>>> multi
>>>>>>> v7 kernel size increases they can clobber memory when they get
>>>>>>> decompressed.
>>>>>>
>>>>>> Thanks, that was it:
>>>>>>
>>>>>> http://nvt.pwsan.com/pub/pwalmsley-tester/testlogs/test_20150325144058_6af714b069dc278d5d8e1b7afc13568f71d9aba8/20150325144058/boot/tegra20-trimslice/tegra20-trimslice/multi_v7_defconfig_log.txt
>>>>>>
>> ...
>>>>> Interesting. Do the values in U-Boot's default environment work
>>>>> correctly
>>>>
>>>> No idea, I haven't tried.  (The load addresses I used are observable in
>>>> the boot logs above.)
>>>
>>> Sure. I was hoping you'd try it out since you already had the setup to
>>> repro the issue.
>>>
>>> It'd be good if your test-bed used the built-in U-Boot variables too, so
>>> we're testing them.
>>
>> I've reproduced the original problem, and then validated that using
>> the addresses from U-Boot's default environment (at least with a ToT
>> U-Boot that I just built) does indeed solve it.
>>
>> I'd like to re-iterate that the test bed should be using the values
>> from U-Boot's environment rather than making up its own. That way:
>>
>> * The value the test bed uses for the kernel load address likely
>> overlaps where the kernel decompressor writes to for even slightly
>> large kernels. This means the decompressor must move itself before
>> decompressing. IIUC, there's zero guarantee that moving the
>> decompressor won't overwrite the DTB, since IIUC the decompressor uses
>> zero knowledge of the DTB location. In other words, if the compressed
>> kernel is loaded somewhere that's likely to require it to move itself,
>> there's a real risk of the exact same problem cropping up again in the
>> future if the kernel happens to overwrite the DTB during relocation.
>>
>> * The values are part of every Tegra U-Boot port (and hopefully for
>> other SoCs too given any distro using boot.scr with
>> config_distro_bootcmd.h will expect the variables to exist), so for
>> future (Tegra) chips you won't have to adjust the test bed if RAM
>> layout changes.
>>
>> * Those values get testing, so we'll find out if the ever don't work.
>> We get more test coverage.
>
> Sounds reasonable, I'll try to get to this at some point soon.
>
> BTW, it might be worth changing U-boot CONFIG_LOADADDR to point to the
> value you define for kernel_addr_r.  That would reinforce to folks who
> aren't using the U-boot scripts that they should use that address for
> loading their kernel.

Hmm. Our values for CONFIG_LOADADDR and CONFIG_SYS_LOADADDR in U-Boot 
seem to be a mess.

Essentially they are used for the same semantic purpose, it's just that 
different U-Boot features use one or the other. I propose we make them 
the same value. There are certainly many other boards that do (and many 
that don't, strangely).

I'm not sure that pointing those at the same location as kernel_addr_r 
is best. I'd expect modern scripts to explicitly use one of the 
type-specific (kernel, DT, script, initrd, ...) variables and never rely 
on simple $loadaddr. How about we point these variables somewhere that 
doesn't overlap with any of the memory regions "reserved"/intended for a 
specific purpose?

In other words, I'd suggest 0x90200000 as the value for Tegra30+; that's 
consistent with the default values of $scriptaddr and $pxefile_addr_r, 
i.e. 1MB beyond the latter, and well out of the way from anything else.

Does all that sound reasonable? If so, I'll send a patch for U-Boot.