riscv: introduce ioremap_wc()

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@bytedance.com>
Signed-off-by: Qingfang Deng <qingfang.deng@siflower.com.cn>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250722091504.45974-2-cuiyunhui@bytedance.com
Signed-off-by: Paul Walmsley <pjw@kernel.org>

Author: cuiyunhui

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 */
 
 /*

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)