Re: [RFC PATCH 0/3] riscv: Add riscv.fwsz kernel parameter to save memory

["Heiko Stübner" <heiko@sntech.de>]

Am Mittwoch, 24. November 2021, 07:42:17 CET schrieb Guo Ren:
> On Wed, Nov 24, 2021 at 3:33 AM Heiko Stübner <heiko@sntech.de> wrote:
> >
> > Hi Guo,
> >
> > Am Dienstag, 23. November 2021, 02:57:14 CET schrieb guoren@kernel.org:
> > > From: Guo Ren <guoren@linux.alibaba.com>
> > >
> > > The firmware of riscv (such as opensbi) occupy 2MB(64bit) /
> > > 4MB(32bit) in Linux. It's very wasteful to small memory footprint
> > > soc chip such as Allwinner D1s/F133. The kernel parameter gives a
> > > chance to users to set the proper size of the firmware and get
> > > more than 1.5MB of memory.
> >
> > is this kernel parameter approach a result of the T-Head Ice-SoC
> > currently loading its openSBI from inside the main u-boot via extfs-load,
> > directly before the kernel itself [0] ?
> The patch is not related to that issue. The patch just helps users who
> put opensbi at 0~2MB paddr to save memory.

So as Anup wrote, this should just be solved by using a correct reserved memory
node in the devicetree passed to the kernel. And the firmware will know what
memory region it actually occupies ;-)


> 
> >
> > Because that approach in general looks not ideal.
> >
> > Normally you want the main u-boot already running with less privileges
> > so firmware like openSBI should've been already loaded before that.
> > Even more true when you're employing methods to protect memory regions
> > from less privileged access.
> >
> > A lot of socs set u-boot as opensbi payload, but for the example the D1
> > mainline approach uses the Allwinner TOC1 image format to load both
> > opensbi and the main uboot into memory from its 1st stage loader.
> >
> >
> > Of course the best way would be to just mimic what a number of
> > arm64 and also riscv socs do and use already existing u-boot utilities.
> >
> > U-Boot can create a FIT image containing both main u-boot, dtb and
> > firmware images that all get loaded from SPL and placed at the correct
> > addresses before having the SPL jump into opensbi and from there
> > into u-boot [1] .
> >
> > And as Anup was writing, reserved-memory should then be the way
> > to go to tell the kernel what regions to omit.
> >
> > And mainline u-boot has already the means to even take the reserved-memory
> > from the devicetree used by opensbi and copy it to a new devicetree,
> > if the second one is different.
> >
> >
> > Heiko
> >
> >
> > [0] https://github.com/T-head-Semi/u-boot/blob/main/include/configs/ice-c910.h#L46
> > [1] see spl_invoke_opensbi() in common/spl/spl_opensbi.c
> > [2] see riscv_board_reserved_mem_fixup() in arch/riscv/lib/fdt_fixup.c
> >
> > >
> > > Guo Ren (3):
> > >   riscv: Remove 2MB offset in the mm layout
> > >   riscv: Add early_param to decrease firmware region
> > >   riscv: Add riscv.fwsz kernel parameter
> > >
> > >  .../admin-guide/kernel-parameters.txt         |  3 +++
> > >  arch/riscv/include/asm/page.h                 |  8 +++++++
> > >  arch/riscv/kernel/head.S                      | 10 +++-----
> > >  arch/riscv/kernel/vmlinux.lds.S               |  5 ++--
> > >  arch/riscv/mm/init.c                          | 23 ++++++++++++++++---
> > >  5 files changed, 36 insertions(+), 13 deletions(-)
> > >
> > >
> >
> >
> >
> >
> 
> 
>