Re: [PATCH 13/15] riscv: clear the instruction cache and all registers when booting

[Christoph Hellwig]

On Wed, Aug 14, 2019 at 09:00:14AM +0800, Alan Kao wrote:
> But it doesn't really mean that the running system has an FPU given CONFIG_FPU
> enabled.  Normally the existence of an FPU is checked in riscv_fill_hwcap by
> searching device tree, where the code looks like
> 
> 
> bool has_fpu = false; // this one is global
> ...
> #ifdef CONFIG_FPU
>         if (elf_hwcap & (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D))
>                 has_fpu = true;
> #endif
> 
> 
> Or does CONFIG_FPU have a more intuitive meaning when CONFIG_M_MODE is enabled?

No, it doesn't..

> 
> > +	csrr	t0, CSR_MISA
> > +	andi	t0, t0, (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D)
> > +	bnez	t0, .Lreset_regs_done

... which is why we have these few lines of code that check the
caps returns from the misa CSR, similar to the elf_caps check quoted
above.