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    SubjectRe: [PATCH] drivers/block/xsysace - replace in(out)_8/in(out)_be16/in(out)_le16 with generic iowrite(read)8/16(be)
    On 02/07/2013 01:34 AM, Arnd Bergmann wrote:
    > On Wednesday 06 February 2013 17:21:37 Michal Simek wrote:
    >
    >> I have looked at the patches from more practical side and I have tested it on
    >> microblaze big endian in 16bit mode and I have found that sysace driver
    >> stop to work.
    >> After that I have looked at ioread/iowrite microblaze implementation
    >> and implementation of that functions is wrong.
    >> I have fixed it but looking at using asm-generic/io.h for microblaze.
    >>
    >> I will do more tests and let you know.
    >
    > Well, I think they are only wrong in the way that they ignore
    > endianess. You can fix that by changing them to be identical
    > to the in_le/in_be families.

    But still it is wrong.

    >
    > However, I would also recommend changing your __raw_* accessors
    > to inline assembly functions rather than pointer dereferences,
    > because we have had problems in the past where gcc (when faced
    > with undefined C) silently turned 32-bit accesses into multiples
    > of byte accesses, which can be fatal for MMIO. The asm-generic
    > version obviously cannot get this right.
    >
    > The PCI I/O space handling, as mentioned, is completely broken
    > on microblaze, and you can either use the approach from asm-generic
    > when you set PCI_IOBASE match your isa_io_base.

    One question regarding to asm-generic/io.h about iowrite16be implementation

    #define iowrite16be(v, addr) iowrite16(be16_to_cpu(v), (addr))
    #define iowrite16(v, addr) writew((v), (addr))
    #define writew(b,addr) __raw_writew(__cpu_to_le16(b),addr)

    static inline void __raw_writew(u16 b, volatile void __iomem *addr)
    {
    *(volatile u16 __force *) addr = b;
    }

    How is this suppose to work on Big Endian?
    be16_to_cpu(v) is (v)
    and
    __cpu_to_le16(b) is swab16(v)

    On little
    be16_to_cpu(v) is swab16(v)
    and
    __cpu_to_le16(swab(b)) is swab16(v)


    What I would expect is
    #define iowrite16be(v, addr) __raw_writew(__cpu_to_be16(v), addr)

    on Big endian:
    __cpu_to_be16(v) is (v)
    on Little endian:
    __cpu_to_be16(v) is swab(v)

    What am I missing here?

    Thanks,
    Michal


    --
    Michal Simek, Ing. (M.Eng)
    w: www.monstr.eu p: +42-0-721842854
    Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
    Microblaze U-BOOT custodian


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