• Christoph Hellwig's avatar
    riscv: add nommu support · 6bd33e1e
    Christoph Hellwig authored
    The kernel runs in M-mode without using page tables, and thus can't run
    bare metal without help from additional firmware.
    
    Most of the patch is just stubbing out code not needed without page
    tables, but there is an interesting detail in the signals implementation:
    
     - The normal RISC-V syscall ABI only implements rt_sigreturn as VDSO
       entry point, but the ELF VDSO is not supported for nommu Linux.
       We instead copy the code to call the syscall onto the stack.
    
    In addition to enabling the nommu code a new defconfig for a small
    kernel image that can run in nommu mode on qemu is also provided, to run
    a kernel in qemu you can use the following command line:
    
    qemu-system-riscv64 -smp 2 -m 64 -machine virt -nographic \
    	-kernel arch/riscv/boot/loader \
    	-drive file=rootfs.ext2,format=raw,id=hd0 \
    	-device virtio-blk-device,drive=hd0
    
    Contains contributions from Damien Le Moal <Damien.LeMoal@wdc.com>.
    Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
    Reviewed-by: default avatarAnup Patel <anup@brainfault.org>
    [paul.walmsley@sifive.com: updated to apply; add CONFIG_MMU guards
     around PCI_IOBASE definition to fix build issues; fixed checkpatch
     issues; move the PCI_IO_* and VMEMMAP address space macros along
     with the others; resolve sparse warning]
    Signed-off-by: default avatarPaul Walmsley <paul.walmsley@sifive.com>
    6bd33e1e
mmio.h 5.7 KB