linux-kernel - Re: [PATCH] ARM: dts: BCM5301X: Extend RAM to full 256MB for Linksys EA6500 V2

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Message-ID: <2beb9364-7b5d-4cf7-9003-2d70122731c3@gmail.com>
Date:   Wed, 12 Jul 2023 19:07:00 +0200
From:   Rafał Miłecki <zajec5@...il.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Christian Marangi <ansuelsmth@...il.com>
Cc:     Florian Fainelli <florian.fainelli@...adcom.com>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        René Kjellerup <rk.katana.steel@...il.com>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Aleksey Nasibulin <alealexpro100@...ru>, stable@...r.kernel.org
Subject: Re: [PATCH] ARM: dts: BCM5301X: Extend RAM to full 256MB for Linksys
 EA6500 V2

On 12.07.2023 17:23, Andrew Lunn wrote:
>> --- a/arch/arm/boot/dts/broadcom/bcm4708-linksys-ea6500-v2.dts
>> +++ b/arch/arm/boot/dts/broadcom/bcm4708-linksys-ea6500-v2.dts
>> @@ -19,7 +19,8 @@ chosen {
>>   
>>   	memory@0 {
>>   		device_type = "memory";
>> -		reg = <0x00000000 0x08000000>;
>> +		reg = <0x00000000 0x08000000>,
>> +		      <0x88000000 0x08000000>;
> 
> So there is a hole in the middle? Does this require any special
> CONFIG_ option to support sparse memory?

This is how RAM is mapped on all known Northstar devices. Using two
blocks.

I've heard there is a way to design Northstar SoC board to have all RAM
in one region but thay requires disabling something (I don't remember
what) and in practice to vendor decided to do that.

AFAIK no extra CONFIG_* option is needed to make Linux map multiple RAM
regions.