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

[Anup Patel]

On Thu, Jun 3, 2021 at 6:27 PM Alex Ghiti <alex@xxxxxxxx> 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@xxxxxxxx> 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@xxxxxxxx>
> >> ---
> >>   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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> >