Re: [PATCH] RISC-V: Place DTB at 3GB boundary instead of 4GB

[Bin Meng]

Hi Atish,

On Fri, Dec 18, 2020 at 3:27 PM Atish Patra <Atish.Patra@wdc.com> wrote:
>
> On Fri, 2020-12-18 at 15:21 +0800, Bin Meng wrote:
> > Hi Atish,
> >
> > On Fri, Dec 18, 2020 at 5:48 AM Atish Patra <atish.patra@wdc.com>
> > wrote:
> > >
> > > Currently, we place the DTB at 2MB from 4GB or end of DRAM which
> > > ever is
> > > lesser. However, Linux kernel can address only 1GB of memory for
> > > RV32.
> > > Thus, it can not map anything beyond 3GB (assuming 2GB is the
> > > starting address).
> > > As a result, it can not process DT and panic if opensbi dynamic
> > > firmware
> > > is used.
> > >
> > > Fix this by placing the DTB at 2MB from 3GB or end of DRAM
> > > whichever is lower.
> > >
> > > Signed-off-by: Atish Patra <atish.patra@wdc.com>
> > > ---
> > >  hw/riscv/boot.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> >
> > With this patch, 32-bit sifive_u still does not boot kernel with the
> > following patch applied on 5.10:
> > https://patchwork.kernel.org/project/linux-riscv/patch/20201217074855.1948743-1-atish.patra@wdc.com/
> >
> > Command I used:
> > $ qemu-system-riscv32 -nographic -M sifive_u -m 1G -smp 5 -kernel
> > arch/riscv/boot/Image
> >
> > 32-bit virt cannot boot the same kernel image with memory set to 2G
> > either:
> > $ qemu-system-riscv32 -nographic -M virt -m 2G -smp 4 -kernel
> > arch/riscv/boot/Image
> >
>
> Hi Bin,
> As mentioned in the email on the linux mailing list, this patch only
> solves 2GB problem. sifive_u problem is solved by Alistair's patch[1].
>
> He is planning to send the PR soon. The issue with sifive_u boot was it
> was failing the 32 bit test earlier resulting a 2MB aligned address
> instead of 4MB.

Ah, I see. However my testing shows that virt with 2G still does not
boot with this patch.

>
> [1] https://www.mail-archive.com/qemu-devel@nongnu.org/msg767886.html
>

Regards,
Bin