[PATCH v4 2/6] m68k: Fix writew(), writel(), readw(), readl() endianness for classic m68k

Daniel Palmer
2026-04-13T09:23:22Z

In Linux these are meant to read a little-endian value and swap
to the CPU endian.

In u-boot for m68k this is currently broken and prevents
virtio-mmio from functioning.

This change is only for classic m68k. Coldfire has read big-endian,
no swap for these in u-boot and Linux and existing drivers probably
depend on this.

Signed-off-by: Daniel Palmer <daniel@thingy.jp>
Tested-by: Angelo Dureghello <angelo@kernel-space.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
---
arch/m68k/include/asm/io.h | 31 ++++++++++++++++++++-----------
1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/arch/m68k/include/asm/io.h b/arch/m68k/include/asm/io.h
index 35ad4a1c0444..2577081d8363 100644
--- a/arch/m68k/include/asm/io.h
+++ b/arch/m68k/include/asm/io.h
@@ -23,18 +23,27 @@
#define __raw_writew(w,addr) ((*(volatile u16 *) (addr)) = (w))
#define __raw_writel(l,addr) ((*(volatile u32 *) (addr)) = (l))

-#define readb(addr) in_8((volatile u8 *)(addr))
-#define writeb(b,addr) out_8((volatile u8 *)(addr), (b))
-#if !defined(__BIG_ENDIAN)
-#define readw(addr) (*(volatile u16 *) (addr))
-#define readl(addr) (*(volatile u32 *) (addr))
-#define writew(b,addr) ((*(volatile u16 *) (addr)) = (b))
-#define writel(b,addr) ((*(volatile u32 *) (addr)) = (b))
+#define readb(addr) in_8((volatile u8 *)(addr))
+#define writeb(b, addr) out_8((volatile u8 *)(addr), (b))
+#ifdef CONFIG_M680x0
+/*
+ * For classic m68k these work the same way as Linux:
+ * Read a little endian value, swap to the CPU endian.
+ */
+#define readw(addr) in_le16((volatile u16 *)(addr))
+#define readl(addr) in_le32((volatile u32 *)(addr))
+#define writew(b, addr) out_le16((volatile u16 *)(addr), (b))
+#define writel(b, addr) out_le32((volatile u32 *)(addr), (b))
#else
-#define readw(addr) in_be16((volatile u16 *)(addr))
-#define readl(addr) in_be32((volatile u32 *)(addr))
-#define writew(b,addr) out_be16((volatile u16 *)(addr),(b))
-#define writel(b,addr) out_be32((volatile u32 *)(addr),(b))
+/*
+ * For coldfire these read a big endian value and use it
+ * as-is. This means that for little endian devices on the
+ * bus like PCI device these won't work as expected currently.
+ */
+#define readw(addr) in_be16((volatile u16 *)(addr))
+#define readl(addr) in_be32((volatile u32 *)(addr))
+#define writew(b, addr) out_be16((volatile u16 *)(addr), (b))
+#define writel(b, addr) out_be32((volatile u32 *)(addr), (b))
#endif

/*
--
2.51.0