linux-kernel - Re: [PATCH v4] ARM64: dts: meson-gx: Add reserved memory zone and usable memory range

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Message-ID: <a312f87d-bd17-2729-1c51-d25be7de9380@baylibre.com>
Date:   Wed, 18 Jan 2017 11:57:22 +0100
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Andreas Färber <afaerber@...e.de>,
        Kevin Hilman <khilman@...libre.com>
Cc:     Olof Johansson <olof@...om.net>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        xypron.glpk@....de,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Carlo Caione <carlo@...one.org>,
        linux-amlogic@...ts.infradead.org,
        "linux-arm-kernel@...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 01/18/2017 01:00 AM, Andreas Färber wrote:
> Hi Neil,
> 
> Am 17.01.2017 um 09:21 schrieb Neil Armstrong:
>> As I finally understand, the real issue here is the usage of the "linux,useable-memory" property that
>> overrides the reg property that is changed by the bootloader to provide the "real" memory size.
> 
> Yes, exactly. It assured that 0..0x01000000 was always unavailable, as
> intended, but at the same time it ignored any lowered or heightened
> upper limit coming from the bootloader side.
> 
> As a rule of thumb, any nodes that have device_type set can be expected
> to be modified during boot.
> 
>> As I understand the mainline U-Boot does it right, and it's a good news, and it seems uEFI need to provide
>> some specialized memory range aswell, but the vendor U-Boot versions only provide the full memory range here.
>> It seems obvious that whatever range is provided by u-boot, the first 16MiB should be reserved.
>>
>> The stress-ng package provides this "stress" command and is used to force the kernel to map more memory
>> zones,
> 
> Thanks, its binary is called stress-ng in openSUSE Tumbleweed. ;)
> 
>> but I also got the issue while running a fully fledged Desktop Environment thanks to the
>> recently merged DRM driver.
> 
> I'll happily test once HDMI is ready. :)
> 
>> You may not be able to trigger the issue since it seems Amlogic reduces this reserved size on GXL/GXM :
>> https://github.com/khadas/linux/commit/698df2c6cfbb0d1a9359743208e83517b31da6ce
>> But it should be confirmed.
> 
> Confirming no issues on three runs on meson-gxm-rbox-pro:
> 
> boxer:~ # stress-ng --vm 4 --vm-bytes 128M --timeout 10s &
> [1] 2528
> boxer:~ # stress-ng: info:  [2528] dispatching hogs: 4 vm
> stress-ng: info:  [2528] cache allocate: default cache size: 256K
> stress-ng: info:  [2528] successful run completed in 10.07s
> 
> [1]+  Done                    stress-ng --vm 4 --vm-bytes 128M --timeout 10s
> boxer:~ # stress-ng --vm 4 --vm-bytes 128M --timeout 10s
> stress-ng: info:  [2537] dispatching hogs: 4 vm
> stress-ng: info:  [2537] cache allocate: default cache size: 256K
> stress-ng: info:  [2537] successful run completed in 10.07s
> boxer:~ # stress-ng --vm 4 --vm-bytes 128M --timeout 10s
> stress-ng: info:  [2546] dispatching hogs: 4 vm
> stress-ng: info:  [2546] cache allocate: default cache size: 256K
> stress-ng: info:  [2546] successful run completed in 10.07s
> boxer:~ #

For 2 GiB boards, you may need to increase the vm threads :
# stress-ng --vm 16 --vm-bytes 128M --timeout 10s
stress-ng: info:  [1292] dispatching hogs: 16 vm
stress-ng: info:  [1292] cache allocate: default cache size: 512K
stress: info: [1275] dispatching hogs: 0 cpu, 0 io, 16 vm, 0 hdd
[  948.832694] Bad mode in Error handler detected on CPU1, code 0xbf000000 -- SError
[  948.832812] Bad mode in Error handler detected on CPU3, code 0xbf000000 -- SError
[  948.832832] CPU: 3 PID: 1279 Comm: stress Not tainted 4.10.0-rc4-00004-gba7e7b8 #14
...

On a Wetek Play2 board with 2GiB.

> 
>> Kevin asked me initially to handle this "start of ddr" reserved zone via a reserved-memory entry, but
>> at that time it seemed a better idea to use "linux,useable-memory", but I recon it may be an error.
>>
>> I will push a v5 with a supplementary reserved-memory entry and will postpone the boards memory size
>> fixup for a future DTS cleanup.
>>
>> Andreas, is this ok for you ?
> 
> Yes, sounds fine to me, thanks. I'll note a few more nits to consider.
> 
> Kevin, I noticed that this supposedly applied patch did not show up in
> linux-next for testing - could you merge your fixes branch into for-next
> please for those of us working on new stuff?
> 
>> This issue exists since forever on mainline linux, and even 4.9 has it.
>> Olof, How could a similar fix go in 4.9 stable ?
> 
> I guess it would then be best to consider splitting this patch up per
> board/SoC so that you can set appropriate Fixes: headers indicating how
> far back each one needs to be fixed.
> 
> Regards,
> Andreas
>