Date:   Mon, 16 Jan 2017 11:39:53 +0100
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Andreas Färber <afaerber@...e.de>,
        Kevin Hilman <khilman@...libre.com>
Cc:     devicetree@...r.kernel.org, xypron.glpk@....de,
        linux-kernel@...r.kernel.org, carlo@...one.org,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4] ARM64: dts: meson-gx: Add reserved memory zone and
 usable memory range

On 01/15/2017 03:43 PM, Andreas Färber wrote:
> Am 13.01.2017 um 21:03 schrieb Kevin Hilman:
>> Neil Armstrong <narmstrong@...libre.com> writes:
>>
>>> The Amlogic Meson GXBB/GXL/GXM secure monitor uses part of the memory space,
>>> this patch adds this reserved zone and redefines the usable memory range.
>>>
>>> The memory node is also moved from the dtsi files into the proper dts files
>>> to handle variants memory sizes.
>>>
>>> This patch also fixes the memory sizes for the following platforms :
>>> - gxl-s905x-p212 : 1GiB instead of 2GiB, a proper 2GiB dts should be pushed
>>> - gxm-s912-q201 : 1GiB instead of 2GiB, a proper 2GiB dts should be pushed
>>> - gxl-s905d-p231 : 1GiB instead of 2GiB, a proper 2GiB dts should be pushed
>>> - gxl-nexbox-a95x : 1GiB instead of 2GiB, a proper 2GiB dts should be pushed
>>>
>>> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
>>
>> Queued for v4.10-rc.
> 
> What is the motivation for this change? I have a local U-Boot patch to
> detect the amount of memory available as done downstream, but U-Boot
> only updates the reg property that you seem to be abandoning here...
> 
> So for devices that come in multiple RAM configurations - like R-Box Pro
> - this would require separate .dts files now! This looks very wrong to
> me, especially since I am not aware of other platforms doing the same.
> Instead, there's memory reservations for top and bottom done in U-Boot
> for reg, plus reserved-memory nodes for anything in the middle.
> 
> Another thing to consider is that uEFI boot (bootefi) handles memory
> reservation differently yet again, on the bootloader level. I have had
> that working fine on Odroid-C2 and Vega S95.
> 
> So if there's no bug this is fixing (none mentioned in commit message) I
> strongly object to this patch.
> 
> Regards,
> Andreas
> 

Hi Andreas,

Like I replied of my RFT patch :
I really disagree about relying on any work or properties added by any bootloader here, Amlogic SoCs has
a lot of u-boot versions in the field, and the Odroid-C2 is part of this.

Even if Odroid-c2 is in mainline U-Boot or not, the mainline Linux kernel should work using
any U-boot version even with the one provided by Amlogic on their openlinux distribution channel.

Handling multiple RAM configuration is another story, and the Arm-Soc and DT maintainers should give us
their advices.

Actually there is a severe bug fixed here that cause a huge crash if such memory is not reserved while
running stock u-boot version on various shipped products and Amlogic's own development boards.

The bug is easily triggered by running :
# stress --vm 4 --vm-bytes 128M --timeout 10s &
[   46.937975] Bad mode in Error handler detected on CPU1, code 0xbf000000 -- SError
...
[   47.058536] Internal error: Attempting to execute userspace memory: 8600000f [#3] PREEMPT SMP
...

Note this is a fix targeted for 4.10 to make the system stable and various users reported some severe
crash now the system has more drivers and read-world use-cases are running on Amlogic SoCs.

Please feel free to push whatever changes that makes this memory reservation more coherent for 4.11,
and respect the behavior of already shipped u-boot version and mainline U-Boot, UEFI, whatever...

Neil

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