[U-Boot] [PATCH v5 4/4] riscv: Remove redundant a2 store on DRAM base in start.S

[Rick Chen]

> > > > > When we run U-Boot in S-mode the BBL runs from 0x80000000 so this
> > > > > two lines corrupts BBL instructions.

Hi Anup

You said
Your patchset based upon git://git.denx.de/u-boot-riscv.git

Why you announce this problem in [PATCH v5 4/4] riscv: Remove
redundant a2 store on DRAM base in start.S
Why you do not find this proble in v1, v2, v3, v4 ?

Rick

> > > > >
> > > > > If this is important for some board then please have it around #ifdef.
> > > > >
> > > >
> > > > Hi Anup
> > > >
> > > > In the discussion as below :
> > > > https://www.mail-archive.com/u-boot@lists.denx.de/msg305880.html
> > > >
> > > > I try to solve this issue with the aptch
> > > > [PATCH] riscv: ax25-ae350: Pass dtb address to u-boot with a1 register
> > > > diff --git a/arch/riscv/cpu/start.S b/arch/riscv/cpu/start.S
> > > > -       li      t0, CONFIG_SYS_SDRAM_BASE
> > > > -       SREG    a2, 0(t0)
> > > >
> > > > diff --git a/board/AndesTech/ax25-ae350/ax25-ae350.c
> > > > b/board/AndesTech/ax25-ae350/ax25-ae350.c
> > > >  void *board_fdt_blob_setup(void)
> > > >  {
> > > > -       void **ptr = (void *)CONFIG_SYS_SDRAM_BASE;
> > > > +       void **ptr = (void *)&prior_stage_fdt_address;
> > > >
> > > > in the previous pull request.
> > > >
> > > > But Bin do not agree with that I use prior_stage_fdt_address in
> > > > board_fdt_blob_setup( )
> > > > I try to explain why I use it like that way.
> > > > Then Bin have not any reply in the following mail.
> > > > Finally I decide to drop this patch in the next pull request.
> > > >
> > > > Hi Bin
> > > >
> > > > How do you think about I recovery this patch to fix this issue ?
> > >
> > > Actually, previous booting stage can pass location of FDT stored in flash
> > > to U-Boot. U-Boot requires FDT at a DRAM location which it can modify
> > > in-place before passing on to Linux kernel so we should relocate the FDT
> > > passed by previous booting stage to some board specific DRAM location.
> > >
> > > My suggestion is as follows:
> > >
> > > Instead of SDRAM_BASE, we can have new board specific config
> > > CONFIG_RISCV_PRIOR_FDT_BASE
> > >
> > > If CONFIG_RISCV_PRIOR_FDT_BASE is defined/selected by
> > > config then in start.S copy-over the FDT from location pointed by
> > > "a1" register to location pointed by CONFIG_RISCV_PRIOR_FDT_BASE.
> >
>
> Hi Anup
>
> It can not achieve dtb delivery at runtime.
>
> Rick
>
> > I think you can copy-over FDT in C code too. You don't need to do
> > in start.S.
> >
> > >
> > > In your board_fdt_blob_setup(), you can safely do:
> > > void **ptr = (void *)CONFIG_RISCV_PRIOR_FDT_BASE;
> > >
> > > Regards,
> > > Anup