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    SubjectRe: [PATCH V2 2/4] MIPS: Add board support for Loongson1B
    From
    2011/10/24, Giuseppe CAVALLARO <peppe.cavallaro@st.com>:
    > On 10/24/2011 4:05 PM, Kelvin Cheung wrote:
    >> 2011/10/24, Giuseppe CAVALLARO <peppe.cavallaro@st.com>:
    >>> Hello Kelvin.
    >>>
    >>> On 10/24/2011 12:36 PM, Kelvin Cheung wrote:
    >>>
    >>> [snip]
    >>>
    >>>> According to datasheet of Loongson 1B, the buffer size in RX/TX
    >>>> descriptor is only 2KB. So the Loongson1B's GMAC could not handle
    >>>> jumbo frames. And the second buffer is useless in this case. Am I
    >>>> right? Is there a better way than ifdef CONFIG_MACH_LOONGSON1 to
    >>>> avoid duplicate code?
    >>>
    >>> Sorry for my misunderstanding.
    >>>
    >>> I think you have to use the normal descriptor and remove the enh_desc
    >>> from the platform w/o modifying the driver at all.
    >>>
    >>> The driver will be able to select/configure all automatically (also
    >>> jumbo).
    >>>
    >>> Let me know.
    >>
    >> That's the problem.
    >> The bitfield definition of Loongson1B is also different from normal
    >> descriptor.
    >
    > The problem is not in the Loongson1B gmac.

    I found that the bit checksum_insertion is not existed in normal descriptor.

    > The normal descriptor fields in the stmmac refer to an old synopsys
    > databook.

    Could you send me the new databook of Synopsys GMAC?

    > New chips have the same structure you have added; so we should fix this
    > in the driver w/o breaking the compatibility for old chips.

    Agree.

    > I kindly ask you to confirm if the currently normal descriptor structure
    > (w/o your changes) doesn't work on your platform.
    > Did you test it?

    Well, the normal descriptor works on my platform except TX checksum offload.

    >> Moreover, I want to enable the TX checksum offload function which is
    >> not supported in normal descriptor.
    >> Any suggestions?
    >
    > It is supported but you have to pass from the platform: tx_coe = 1.

    I noticed that the flag csum_insertion is passed to
    ndesc_prepare_tx_desc() in stmmac_xmit(). But ndesc_prepare_tx_desc()
    just ignores it.
    In other words, the TX checksum offload function is disabled in normal
    descriptor currently.

    Should we fix this problem for normal descriptor?

    > Peppe
    >>
    >>> Note:
    >>> IIRC, there is a bit difference in case of normal descriptors for
    >>> Synopsys databook newer than the 1.91 (I used for testing this mode).
    >>> In any case, I remember that, on some platforms, the normal descriptors
    >>> have been used w/o problems also on these new chip generations.
    >>>
    >>> Peppe
    >>>
    >>>
    >>
    >>
    >
    >


    --
    Best Regards!
    Kelvin


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