Re: [PATCH 15/15] riscv: disable the EFI PECOFF header for M-mode

[Atish Patra]

On Tue, 2019-08-20 at 21:14 -0700, Troy Benjegerdes wrote:
> > On Aug 13, 2019, at 8:47 AM, Christoph Hellwig <hch@xxxxxx> wrote:
> > 
> > No point in bloating the kernel image with a bootloader header if
> > we run bare metal.
> 
> I would say the same for S-mode. EFI booting should be an option, not
> a requirement. 

EFI booting is never a requirement on any board. When EFI stub will be
added for kernel, it will be enabled with CONFIG_EFI_STUB only. 

The current additional header is only 64 bytes and also required for
booti in U-boot. So it shouldn't disabled for S-mode.
 
Disabling it for M-Mode Linux is okay because of memory constraint and
M-Mode linux won't use U-boot anyways.

> I have M-mode U-boot working with bootelf to start BBL,
> and at some point, Iâm hoping we can have a M-mode linux kernel be
> the SBI provider for S-mode kernels, 

Why do you want bloat a M-Mode software with Linux just for SBI
implementation?

Using Linux as a last stage boot loader i.e. LinuxBoot may make sense
though.

> which seem most logical to me
> to start using the vmlinux elf binaries using something like kexec()
> 
> > Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> > ---
> > arch/riscv/kernel/head.S | 2 ++
> > 1 file changed, 2 insertions(+)
> > 
> > diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> > index 670e5cacb24e..09fcf3d000c0 100644
> > --- a/arch/riscv/kernel/head.S
> > +++ b/arch/riscv/kernel/head.S
> > @@ -16,6 +16,7 @@
> > 
> > __INIT
> > ENTRY(_start)
> > +#ifndef CONFIG_M_MODE
> > 	/*
> > 	 * Image header expected by Linux boot-loaders. The image
> > header data
> > 	 * structure is described in asm/image.h.
> > @@ -47,6 +48,7 @@ ENTRY(_start)
> > 
> > .global _start_kernel
> > _start_kernel:
> > +#endif /* CONFIG_M_MODE */
> > 	/* Mask all interrupts */
> > 	csrw CSR_XIE, zero
> > 	csrw CSR_XIP, zero
> > -- 
> > 2.20.1
> > 
> > 
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> 
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-- 
Regards,
Atish