Re: [PATCH v3 2/5] m68k: Fix writew(), writel(), readw(), readl() endianness for classic m68k

[Angelo Dureghello <angelo@kernel-space.org>]

Tested-by: Angelo Dureghello <angelo@kernel-space.org>


it's mainly ok, btw, since you need still probably a v4,
see below:

On 4/9/26 00:09, 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>
> ---
>  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))

My understanding is that, even if m68k is big endian, you need 
LE r/w for usage with virtio. 

Would M680x0 non-qemu work still with this change ?
Maybe an #if defined (CONFIG_VIRTIO) && defined(CONFIG_M680x0)
would be better ?


>  #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
>  
>  /*

Regards,
-- Angelo