linux-kernel - [PATCH] iommu: riscv: Split 8-byte accesses on 32 bit I/O bus platform

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Message-Id: <20250325144252.27403-1-luxu.kernel@bytedance.com>
Date: Tue, 25 Mar 2025 22:42:52 +0800
From: Xu Lu <luxu.kernel@...edance.com>
To: tjeznach@...osinc.com,
	joro@...tes.org,
	will@...nel.org,
	robin.murphy@....com,
	alex@...ti.fr
Cc: lihangjing@...edance.com,
	xieyongji@...edance.com,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev,
	Xu Lu <luxu.kernel@...edance.com>
Subject: [PATCH] iommu: riscv: Split 8-byte accesses on 32 bit I/O bus platform

Introduce a new configuration CONFIG_RISCV_IOMMU_32BIT to enable
splitting 8-byte access into 4-byte transactions for hardware platform
whose I/O bus limits access to 4-byte transfers.

Signed-off-by: Xu Lu <luxu.kernel@...edance.com>
---
 drivers/iommu/riscv/Kconfig |  9 +++++++++
 drivers/iommu/riscv/iommu.h | 28 +++++++++++++++++++++++-----
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/riscv/Kconfig b/drivers/iommu/riscv/Kconfig
index c071816f59a6..b7c9ea22d969 100644
--- a/drivers/iommu/riscv/Kconfig
+++ b/drivers/iommu/riscv/Kconfig
@@ -18,3 +18,12 @@ config RISCV_IOMMU_PCI
 	def_bool y if RISCV_IOMMU && PCI_MSI
 	help
 	  Support for the PCIe implementation of RISC-V IOMMU architecture.
+
+config RISCV_IOMMU_32BIT
+	bool "Support 4-Byte Accesses on RISC-V IOMMU Registers"
+	depends on RISCV_IOMMU
+	default n
+	help
+	  Support hardware platform whose I/O bus limits access to 4-byte
+	  transfers. When enabled, all accesses to IOMMU registers will be
+	  split into 4-byte accesses.
diff --git a/drivers/iommu/riscv/iommu.h b/drivers/iommu/riscv/iommu.h
index 46df79dd5495..0e3552a8142d 100644
--- a/drivers/iommu/riscv/iommu.h
+++ b/drivers/iommu/riscv/iommu.h
@@ -14,6 +14,10 @@
 #include <linux/iommu.h>
 #include <linux/types.h>
 #include <linux/iopoll.h>
+#ifdef CONFIG_RISCV_IOMMU_32BIT
+#include <linux/io-64-nonatomic-hi-lo.h>
+#include <linux/io-64-nonatomic-lo-hi.h>
+#endif
 
 #include "iommu-bits.h"
 
@@ -69,21 +73,35 @@ void riscv_iommu_disable(struct riscv_iommu_device *iommu);
 #define riscv_iommu_readl(iommu, addr) \
 	readl_relaxed((iommu)->reg + (addr))
 
-#define riscv_iommu_readq(iommu, addr) \
-	readq_relaxed((iommu)->reg + (addr))
-
 #define riscv_iommu_writel(iommu, addr, val) \
 	writel_relaxed((val), (iommu)->reg + (addr))
 
+#define riscv_iommu_readl_timeout(iommu, addr, val, cond, delay_us, timeout_us) \
+	readx_poll_timeout(readl_relaxed, (iommu)->reg + (addr), val, cond, \
+			   delay_us, timeout_us)
+
+#ifndef CONFIG_RISCV_IOMMU_32BIT
+#define riscv_iommu_readq(iommu, addr) \
+	readq_relaxed((iommu)->reg + (addr))
+
 #define riscv_iommu_writeq(iommu, addr, val) \
 	writeq_relaxed((val), (iommu)->reg + (addr))
 
 #define riscv_iommu_readq_timeout(iommu, addr, val, cond, delay_us, timeout_us) \
 	readx_poll_timeout(readq_relaxed, (iommu)->reg + (addr), val, cond, \
 			   delay_us, timeout_us)
+#else /* CONFIG_RISCV_IOMMU_32BIT */
+#define riscv_iommu_readq(iommu, addr) \
+	hi_lo_readq_relaxed((iommu)->reg + (addr))
 
-#define riscv_iommu_readl_timeout(iommu, addr, val, cond, delay_us, timeout_us) \
-	readx_poll_timeout(readl_relaxed, (iommu)->reg + (addr), val, cond, \
+#define riscv_iommu_writeq(iommu, addr, val) \
+	((addr == RISCV_IOMMU_REG_IOHPMCYCLES) ? \
+	 lo_hi_writeq_relaxed((val), (iommu)->reg + (addr)) : \
+	 hi_lo_writeq_relaxed((val), (iommu)->reg + (addr)))
+
+#define riscv_iommu_readq_timeout(iommu, addr, val, cond, delay_us, timeout_us) \
+	readx_poll_timeout(hi_lo_readq_relaxed, (iommu)->reg + (addr), val, cond, \
 			   delay_us, timeout_us)
+#endif /* CONFIG_RISCV_IOMMU_32BIT */
 
 #endif
-- 
2.20.1