linux-kernel - [PATCH 1/1] riscv: introduce ioremap

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Message-Id: <20250722091504.45974-2-cuiyunhui@bytedance.com>
Date: Tue, 22 Jul 2025 17:15:04 +0800
From: Yunhui Cui <cuiyunhui@...edance.com>
To: paul.walmsley@...ive.com,
	palmer@...belt.com,
	aou@...s.berkeley.edu,
	alex@...ti.fr,
	akpm@...ux-foundation.org,
	catalin.marinas@....com,
	anshuman.khandual@....com,
	kas@...nel.org,
	ryan.roberts@....com,
	cuiyunhui@...edance.com,
	samuel.holland@...ive.com,
	namcao@...utronix.de,
	willy@...radead.org,
	abrestic@...osinc.com,
	yongxuan.wang@...ive.com,
	apopple@...dia.com,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Cc: Qingfang Deng <qingfang.deng@...lower.com.cn>
Subject: [PATCH 1/1] 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@...edance.com>
Signed-off-by: Qingfang Deng <qingfang.deng@...lower.com.cn>
---
 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)
 
-- 
2.39.5