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

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Date:   Mon, 16 Jan 2017 11:26:58 +0100
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Andreas Färber <afaerber@...e.de>,
        Heinrich Schuchardt <xypron.glpk@....de>
Cc:     khilman@...libre.com, carlo@...one.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org
Subject: Re: [RFT PATCH] ARM64: dts: meson-gxbb: Add reserved memory zone and
 usable memory range

On 01/15/2017 04:44 PM, Andreas Färber wrote:
> Am 23.12.2016 um 10:42 schrieb Heinrich Schuchardt:
>> it really makes a difference if we write
>>
>>  	memory@0 {
>>  		device_type = "memory";
>>  		linux,usable-memory = <0x0 0x1000000 0x0 0x7f000000>;
>>  	};
>>
>> or
>>
>>  	memory@0 {
>>  		device_type = "memory";
>>  		reg = <0x0 0x1000000 0x0 0x7f000000>;
>>  	};
>>
>> The second version leads to failure of the Odroid C2.
>>
>> When I looked at /sys/firmware/fdt I saw this difference:
>>
>> --- fails
>> +++ works
>>
>>         memory@0 {
>> -               device_type = "memory";
>>                 reg = <0x0 0x0 0x0 0x78000000>;
>> +               device_type = "memory";
>> +               linux,usable-memory = <0x0 0x1000000 0x0 0x7f000000>;
>>         };
>>
>> I found the following sentence in the NXP forum:
>> In case you want to overwrite the memory usage passed from u-boot, you
>> can use "linux,usable-memory".
>> https://community.nxp.com/thread/382284
> 
> The Odroid-C2 is in mainline U-Boot. Please submit a patch to U-Boot
> instead of forcing the creation of unnecessary new .dts files onto
> everyone due to hardcoded linux,usable-memory properties. In fact, it
> already reserves 0x1000000, so it seems you are merely using an older
> U-Boot.
> 
> http://git.denx.de/?p=u-boot.git;a=blob;f=arch/arm/mach-meson/board.c;h=f159cbf849f75ab046e6f3a025bbc97c0bcfd59d;hb=HEAD#l39
> 
> I would bet that the upper limit is unrelated here.
> 
> Regards,
> Andreas
> 

Hi Andreas,

I really disagree about relying on any work or properties added by any bootloader here, Amlogic SoCs has
a lot of u-boot version 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.

Neil