94c2b6aff4
A Malta board can support up to 2GiB of RAM. Since the unmapped kseg0/1 regions are only 512MiB large & the latter 256MiB of those are taken up by the IO region, access to RAM beyond 256MiB must be done through a mapped region. In the case of a Linux guest this means we need to use highmem. The mainline Linux kernel does not support highmem for Malta at this time, however this can be tested using the linux-mti-3.8 kernel branch available from: git://git.linux-mips.org/pub/scm/linux-mti.git You should be able to boot a Linux kernel built from the linux-mti-3.8 branch, with CONFIG_HIGHMEM enabled, using 2GiB RAM by passing "-m 2G" to QEMU and appending the following kernel parameters: mem=256m@0x0 mem=256m@0x90000000 mem=1536m@0x20000000 Note that the upper half of the physical address space of a Malta mirrors the lower half (hence the 2GiB limit) except that the IO region (0x10000000-0x1fffffff in the lower half) is not mirrored in the upper half. That is, physical addresses 0x90000000-0x9fffffff access RAM rather than the IO region, resulting in a physical address space resembling the following: 0x00000000 -> 0x0fffffff RAM 0x10000000 -> 0x1fffffff I/O 0x20000000 -> 0x7fffffff RAM 0x80000000 -> 0x8fffffff RAM (mirror of 0x00000000 -> 0x0fffffff) 0x90000000 -> 0x9fffffff RAM 0xa0000000 -> 0xffffffff RAM (mirror of 0x20000000 -> 0x7fffffff) The second mem parameter provided to the kernel above accesses the second 256MiB of RAM through the upper half of the physical address space, making use of the aliasing described above in order to avoid the IO region and use the whole 2GiB RAM. The memory setup may be seen as 'backwards' in this commit since the 'real' memory is mapped in the upper half of the physical address space and the lower half contains the aliases. On real hardware it would be typical to see the upper half of the physical address space as the alias since the bus addresses generated match the lower half of the physical address space. However since the memory accessible in the upper half of the physical address space is uninterrupted by the IO region it is easiest to map the RAM as a whole there, and functionally it makes no difference to the target code. Due to the requirements of accessing the second 256MiB of RAM through a mapping to the upper half of the physical address space it is usual for the bootloader to indicate a maximum of 256MiB memory to a kernel. This allows kernels which do not support such access to boot on systems with more than 256MiB of RAM. It is also the behaviour assumed by Linux. QEMUs small generated bootloader is modified to provide this behaviour. Signed-off-by: Paul Burton <paul.burton@imgtec.com> Signed-off-by: Yongbok Kim <yongbok.kim@imgtec.com> Reviewed-by: Aurelien Jarno <aurelien@aurel32.net> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net> |
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| .. | ||
| addr.c | ||
| cputimer.c | ||
| gt64xxx_pci.c | ||
| Makefile.objs | ||
| mips_fulong2e.c | ||
| mips_int.c | ||
| mips_jazz.c | ||
| mips_malta.c | ||
| mips_mipssim.c | ||
| mips_r4k.c | ||