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    SubjectRe: [PATCH 2/5] drivers/net/ethernet/dec/tulip: Use standard __set_bit_le() function
    From
    On Wed, Jun 13, 2012 at 7:00 AM, Takuya Yoshikawa
    <takuya.yoshikawa@gmail.com> wrote:
    > On Wed, 13 Jun 2012 22:31:13 +0900
    > Akinobu Mita <akinobu.mita@gmail.com> wrote:
    >
    >> >> Should this hash_table be converted from u16 hash_table[32] to
    >> >> DECLARE_BITMAP(hash_table, 16 * 32) to ensure that it is aligned
    >> >> on long-word boundary?
    >> >
    >> > I think hash_table is already long-word aligned because it is placed
    >> > right after a pointer.
    >>
    >> I recommend converting to proper bitmap.  Because such an implicit
    >> assumption is easily broken by someone touching this function.
    >
    > Do you mean something like:
    >        DECLARE_BITMAP(__hash_table, 16 * 32);
    >        u16 *hash_table = (u16 *)__hash_table;
    > ?
    >
    > Grant, what do you think about this?

    Hi Takuya,
    two thoughts:
    1) while I agree with Akinobu and thank him for pointing out a
    _potential_ alignment problem, this is a separate issue and your
    existing patch should go in anyway. There are probably other drivers
    with _potential_ alignment issues. Akinobu could get credit for
    finding them by submitting patches after reviewing calls to set_bit
    and set_bit_le() - similar to what you are doing now.

    2) I generally do not like declaring one type and then using an alias
    of a different type to reference the same memory address. We have a
    simple alternative since hash_table[] is indexed directly only in one
    hunk of code:
    for (i = 0; i < 32; i++) {
    *setup_frm++ = ((u16 *)hash_table)[i];
    *setup_frm++ = ((u16 *)hash_table)[i];
    }

    thanks,
    grant

    >
    >        Takuya
    >
    >
    > ===
    > drivers/net/ethernet/dec/tulip/tulip_core.c:
    >
    > static void build_setup_frame_hash(u16 *setup_frm, struct net_device *dev)
    > {
    >        struct tulip_private *tp = netdev_priv(dev);
    >        u16 hash_table[32];
    >        ...
    > }
    >
    > drivers/net/ethernet/dec/tulip/de2104x.c:
    >
    > static void build_setup_frame_hash(u16 *setup_frm, struct net_device *dev)
    > {
    >        struct de_private *de = netdev_priv(dev);
    >        u16 hash_table[32];
    >        ...
    > }
    --
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