linux-kernel - Re: [PATCH 4/5] ARM: BCM5301X: Specify all RAM by including extra block

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Date:   Tue, 6 Dec 2016 21:57:31 +0100
From:   Rafał Miłecki <zajec5@...il.com>
To:     Jon Mason <jon.mason@...adcom.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH 4/5] ARM: BCM5301X: Specify all RAM by including extra block

On 6 December 2016 at 21:06, Jon Mason <jon.mason@...adcom.com> wrote:
> On Tue, Dec 06, 2016 at 06:17:13PM +0100, Rafał Miłecki wrote:
>> From: Rafał Miłecki <rafal@...ecki.pl>
>>
>> So far we were specifying only the first block which is always limited
>> up to 128 MiB. There are many devices with 256 MiB and few with 512 MiB.
>
> Assuming that NS is like NSP (and I'm pretty sure it is), there are 2
> ways to access the first 128M of RAM, a proxy starting at address 0
> and the real address.  I think you are splitting RAM by accessing it
> both ways, when you really should just be accessing it at the real
> address.

I need some more help, please.

This patch (quite well tested) confirms that 0x88000000 can be used to
access RAM at offset 128 MiB. If this is a real address and whole
space is contiguous, it means the base real address should be
0x80000000. So using 0x0 and 0x80000000 should allow accessing
beginning of the RAM. I took a device that was working just fine with:
reg = <0x00000000 0x08000000>;
and I replaced it with:
reg = <0x80000000 0x08000000>;
but it broke things, kernel didn't boot with the last message being:
[    0.000000] Memory policy: Data cache writealloc

I can see that bcm958525er.dts, bcm958525xmc.dts, bcm958623hr.dts,
bcm958625k.dts bcm988312hr.dts are using 0x60000000 as base address.
It seems to be different from Northstar but I tried following entry
anyway:
reg = <0x60000000 0x08000000>;
and I got kernel hang just like in the previous try.

Did I miss something? Or does Northstar seem to be actually different than NSP?