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

[Jisheng Zhang]

On Thu, 3 Jun 2021 18:46:47 +0530
Anup Patel <anup@xxxxxxxxxxxxxx> wrote:

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

Hi,

> >
> > 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

For readability, we still can avoid introducing va_kernel_xip_pa_offset
symbol by simply define va_kernel_xip_pa_offset as 0 if XIP as you did
for XIP_OFFSET

PS: this may need a preparation patch:
http://lists.infradead.org/pipermail/linux-riscv/2021-June/006802.html

> > 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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> > > linux-riscv@xxxxxxxxxxxxxxxxxxx
> > > http://lists.infradead.org/mailman/listinfo/linux-riscv
> > >