Re: [PATCH v3 1/3] riscv: Factorize xip and !xip kernel address conversion macros

Anup Patel
2021-06-03T13:18:31Z

On Thu, Jun 3, 2021 at 6:27 PM Alex Ghiti <alex@ghiti.fr> wrote:
>
> Hi Jisheng,
>
> Le 3/06/2021 à 14:27, Jisheng Zhang a écrit :
> > On Thu, 3 Jun 2021 10:27:47 +0200
> > Alexandre Ghiti <alex@ghiti.fr> wrote:
> >
> >> To simplify the kernel address conversion code, make the same definition of
> >> kernel_mapping_pa_to_va and kernel_mapping_va_to_pa compatible for both xip
> >> and !xip kernel by defining XIP_OFFSET to 0 in !xip kernel.
> >>
> >> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> >> ---
> >> arch/riscv/include/asm/page.h | 14 +++-----------
> >> arch/riscv/include/asm/pgtable.h | 2 ++
> >> 2 files changed, 5 insertions(+), 11 deletions(-)
> >>
> >> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> >> index 6a7761c86ec2..6e004d8fda4d 100644
> >> --- a/arch/riscv/include/asm/page.h
> >> +++ b/arch/riscv/include/asm/page.h
> >> @@ -93,9 +93,7 @@ extern unsigned long va_pa_offset;
> >> #ifdef CONFIG_64BIT
> >> extern unsigned long va_kernel_pa_offset;
> >> #endif
> >> -#ifdef CONFIG_XIP_KERNEL
> >> extern unsigned long va_kernel_xip_pa_offset;
> >> -#endif
> >> extern unsigned long pfn_base;
> >> #define ARCH_PFN_OFFSET (pfn_base)
> >> #else
> >> @@ -103,6 +101,7 @@ extern unsigned long pfn_base;
> >> #ifdef CONFIG_64BIT
> >> #define va_kernel_pa_offset 0
> >> #endif
> >> +#define va_kernel_xip_pa_offset 0
> >> #define ARCH_PFN_OFFSET (PAGE_OFFSET >> PAGE_SHIFT)
> >> #endif /* CONFIG_MMU */
> >>
> >> @@ -110,29 +109,22 @@ extern unsigned long kernel_virt_addr;
> >>
> >> #ifdef CONFIG_64BIT
> >> #define linear_mapping_pa_to_va(x) ((void *)((unsigned long)(x) + va_pa_offset))
> >> -#ifdef CONFIG_XIP_KERNEL
> >> #define kernel_mapping_pa_to_va(y) ({ \
> >> unsigned long _y = y; \
> >> (_y >= CONFIG_PHYS_RAM_BASE) ?
> >
> > This CONFIG_PHYS_RAM_BASE is only available for XIP, could result in a
> > compiler error for !XIP?
>
> You're right, I have this patch in my branch and forgot to squash it.
>
> >
> > I'm also concerned with the unecessary overhead of kernel_mapping_pa_to_va()
> > for !XIP case, there's a "if" condition branch, and extra symbol: va_kernel_xip_pa_offset
>
> I understand your concerns even if I don't find that the overhead is
> that important here, I prefer the readability improvement. I can always
> add unlikely/likely builtin to improve things or completely remove this
> patch if others agree with you.

I would also prefer readable code for long-term maintainability. Currently,
the nested "#ifdefs" are increasing causing developers to easily break
untested combinations.

Regards,
Anup

>
> Thanks,
>
> Alex
>
> >
> >> (void *)((unsigned long)(_y) + va_kernel_pa_offset + XIP_OFFSET) : \
> >> (void *)((unsigned long)(_y) + va_kernel_xip_pa_offset); \
> >> })
> >> -#else
> >> -#define kernel_mapping_pa_to_va(x) ((void *)((unsigned long)(x) + va_kernel_pa_offset))
> >> -#endif
> >> #define __pa_to_va_nodebug(x) linear_mapping_pa_to_va(x)
> >>
> >> #define linear_mapping_va_to_pa(x) ((unsigned long)(x) - va_pa_offset)
> >> -#ifdef CONFIG_XIP_KERNEL
> >> #define kernel_mapping_va_to_pa(y) ({ \
> >> unsigned long _y = y; \
> >> (_y < kernel_virt_addr + XIP_OFFSET) ? \
> >> ((unsigned long)(_y) - va_kernel_xip_pa_offset) : \
> >> ((unsigned long)(_y) - va_kernel_pa_offset - XIP_OFFSET); \
> >> })
> >
> > Similar as kernel_mapping_pa_to_va(), an overhead of "if" condition branch
> > for !XIP and extra va_kernel_xip_pa_offset symbol.
> >
> >> -#else
> >> -#define kernel_mapping_va_to_pa(x) ((unsigned long)(x) - va_kernel_pa_offset)
> >> -#endif
> >> +
> >> #define __va_to_pa_nodebug(x) ({ \
> >> unsigned long _x = x; \
> >> (_x < kernel_virt_addr) ? \
> >> @@ -141,7 +133,7 @@ extern unsigned long kernel_virt_addr;
> >> #else
> >> #define __pa_to_va_nodebug(x) ((void *)((unsigned long) (x) + va_pa_offset))
> >> #define __va_to_pa_nodebug(x) ((unsigned long)(x) - va_pa_offset)
> >> -#endif
> >> +#endif /* CONFIG_64BIT */
> >>
> >> #ifdef CONFIG_DEBUG_VIRTUAL
> >> extern phys_addr_t __virt_to_phys(unsigned long x);
> >> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> >> index bde8ce3bfe7c..d98e931a31e5 100644
> >> --- a/arch/riscv/include/asm/pgtable.h
> >> +++ b/arch/riscv/include/asm/pgtable.h
> >> @@ -77,6 +77,8 @@
> >>
> >> #ifdef CONFIG_XIP_KERNEL
> >> #define XIP_OFFSET SZ_8M
> >> +#else
> >> +#define XIP_OFFSET 0
> >> #endif
> >>
> >> #ifndef __ASSEMBLY__
> >
> >
> >
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> >