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

Alex Ghiti
2021-06-03T15:07:17Z

Le 3/06/2021 à 15:53, Jisheng Zhang a écrit :
> On Thu, 3 Jun 2021 18:46:47 +0530
> Anup Patel <anup@brainfault.org> wrote:
>
>> On Thu, Jun 3, 2021 at 6:27 PM Alex Ghiti <alex@ghiti.fr> 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@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
>
> 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

IIUC, that won't improve readability, just avoid to allocate
va_kernel_xip_pa_offset in !XIP kernel right?

>
>>> 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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>>>>
>
>
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