Re: [PATCH 1/1] riscv: introduce ioremap_wc()

[Alexandre Ghiti]

Hi Yunhui,

On 7/22/25 11:15, Yunhui Cui wrote:
> Compared with IO attributes, NC attributes can improve performance,
> specifically in these aspects: Relaxed Order, Gathering, Supports Read
> Speculation, Supports Unaligned Access.
>
> Signed-off-by: Yunhui Cui <cuiyunhui@xxxxxxxxxxxxx>
> Signed-off-by: Qingfang Deng <qingfang.deng@xxxxxxxxxxxxxxx>
> ---
>   arch/riscv/include/asm/io.h      | 4 ++++
>   arch/riscv/include/asm/pgtable.h | 1 +
>   2 files changed, 5 insertions(+)
>
> diff --git a/arch/riscv/include/asm/io.h b/arch/riscv/include/asm/io.h
> index a0e51840b9db4..09bb5f57a9d34 100644
> --- a/arch/riscv/include/asm/io.h
> +++ b/arch/riscv/include/asm/io.h
> @@ -28,6 +28,10 @@
>   #ifdef CONFIG_MMU
>   #define IO_SPACE_LIMIT		(PCI_IO_SIZE - 1)
>   #define PCI_IOBASE		((void __iomem *)PCI_IO_START)
> +
> +#define ioremap_wc(addr, size)	\
> +	ioremap_prot((addr), (size), __pgprot(_PAGE_KERNEL_NC))
> +
>   #endif /* CONFIG_MMU */
>   
>   /*
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 91697fbf1f901..3d17399a06c77 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -203,6 +203,7 @@ extern struct pt_alloc_ops pt_ops __meminitdata;
>   
>   #define PAGE_TABLE		__pgprot(_PAGE_TABLE)
>   
> +#define _PAGE_KERNEL_NC ((_PAGE_KERNEL & ~_PAGE_MTMASK) | _PAGE_NOCACHE)
>   #define _PAGE_IOREMAP	((_PAGE_KERNEL & ~_PAGE_MTMASK) | _PAGE_IO)
>   #define PAGE_KERNEL_IO		__pgprot(_PAGE_IOREMAP)
>   


I have just confirmed with Ved that mapping WC to NC is the correct 
thing to do, so:

Reviewed-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>

And I'll take that for 6.17.

Thanks,

Alex