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

Kuan-Wei Chiu
2026-04-16T09:25:31Z

On Mon, Apr 13, 2026 at 06:22:36PM +0900, Daniel Palmer wrote:
> 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>

Acked-by: Kuan-Wei Chiu <visitorckw@gmail.com>

Regards,
Kuan-Wei

> ---
> 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
>