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WOW64; rv:68.0) Gecko/20100101 Firefox/68.0 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: devicetree-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On 4/7/2020 10:14 PM, Chris Packham wrote: > Hi All, > > I'm trying to port an old Broadcom MIPS CPU (BCM53003) to a shiny new > kernel. I have some old historic source from a long forgotten Broadcom > LDK but I'd prefer to do things the modern way with device-trees. This is a MIPS74Kc CPU, right? > > The problem I've been grappling with is trying to open up access to all > of the RAM on the board. It has 512MB of DDR2. The CPU has two areas > where this appears. The first 128MB is from 0 to 0x07ffffff the second > area is from 0x88000000 to 0x9fffffff. > > SoC peripherals are at 0x18000000 and there is an IO window for flash > at 0x20000000. > > The old code has some custom tlb initialisation to deal with this but I > figured it should be possible with the following dts snippet. > > memory@0 { > device_type = "memory"; > reg = <0x00000000 0x08000000 > 0x88000000 0x18000000>; > }; > > I end up with only 128MB available. This appears to be > because the default HIGHMEM_START of 0x20000000 stops the rest from > being made available. If I add an override of HIGHMEM_START to > 0xffffffff I seem to have the full 512MB avaiable but then I get a > kernel panic Given the SoC supports 128MB or 256MB of EBI space, I suppose you could try setting HIGHMEM_START to 0x2000_0000 + 256MB = 0x3000_0000 and see if it works better. There is also this comment in arch/mips/include/asm/mach-malta/spaces.h regarding the last 64KB of HIGHMEM: * The last 64KB of physical memory are reserved for correct HIGHMEM * macros arithmetics. #define HIGHMEM_START _AC(0xffff0000, UL) > > CPU 0 Unable to handle kernel paging request at virtual address 1fc00000, epc == 800167b8, ra == 800e2860 > > 0x1fc00000 is in the range where the SoC peripherals are so I'm > thinking that is the problem. But then again that is a virtual address > so maybe it's just a co-incidence. 0x1fc0_0000 should be accessed via KSEG0/1 since the physical address is within the first 512MB of physical memory so it should not cause a translation fault since it is unmapped. > > Anyway I'd really appreciate any guidance that anyone could provide on > this. Even if it's just "go look at this SoC". > > Thanks, > Chris > > -- Florian