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Subject: Re: [PATCH v3 1/3] riscv: Factorize xip and !xip kernel address
 conversion macros
To:     Jisheng Zhang <jszhang3@mail.ustc.edu.cn>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Jisheng Zhang <jszhang@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        Zong Li <zong.li@sifive.com>, Anup Patel <anup@brainfault.org>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20210603082749.1256129-1-alex@ghiti.fr>
 <20210603082749.1256129-2-alex@ghiti.fr> <20210603202748.2775f739@xhacker>
From:   Alex Ghiti <alex@ghiti.fr>
Message-ID: <64cdb4f9-06f0-59b9-acf9-6fc298db37d7@ghiti.fr>
Date:   Thu, 3 Jun 2021 14:57:25 +0200
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Hi Jisheng,

Le 3/06/2021 ? 14:27, Jisheng Zhang a ?crit?:
> 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.

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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