netdev - Re: [PATCH 11/20] octeontx2-af: Add support for stripping STAG/CTAG

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Date:   Fri, 9 Nov 2018 22:36:04 +0530
From:   Sunil Kovvuri <sunil.kovvuri@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Linux Netdev List <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>, linux-soc@...r.kernel.org,
        Tomasz Duszynski <tduszynski@...vell.com>,
        Sunil Goutham <sgoutham@...vell.com>
Subject: Re: [PATCH 11/20] octeontx2-af: Add support for stripping STAG/CTAG

On Fri, Nov 9, 2018 at 4:42 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Fri, Nov 9, 2018 at 5:29 AM Sunil Kovvuri <sunil.kovvuri@...il.com> wrote:
> > On Fri, Nov 9, 2018 at 2:17 AM Arnd Bergmann <arnd@...db.de> wrote:
> > > On Thu, Nov 8, 2018 at 7:37 PM <sunil.kovvuri@...il.com> wrote:
>
> > >
> > > Here is another instance of bitfields in an interface structure. As
> > > before, please try to avoid doing that and use bit shifts and masks
> > > instead.
> > >
> > >        Arnd
> >
> > No, this struct is not part of communication interface.
> > This is used to fill up a register in a bit more readable fashion
> > instead of plain bit shifts.
>
> But this is still an interface, isn't it? Writing to the register
> implies that there is some hardware that interprets the
> bits, so they have to be in the right place.
>
> > ===
> > struct nix_rx_vtag_action vtag_action;
> >
> >         *(u64 *)&vtag_action = 0;
> >         vtag_action.vtag0_valid = 1;
> >         /* must match type set in NIX_VTAG_CFG */
> >         vtag_action.vtag0_type = 0;
> >         vtag_action.vtag0_lid = NPC_LID_LA;
> >         vtag_action.vtag0_relptr = 12;
> >         entry.vtag_action = *(u64 *)&vtag_action;
> >
> >         /* Set TAG 'action' */
> >         rvu_write64(rvu, blkaddr, NPC_AF_MCAMEX_BANKX_TAG_ACT(index, actbank),
> >                     entry->vtag_action);
>
> I assume this rvu_write64() does a cpu_to_le64() swap on big-endian,
> so the contents again are in the wrong place. I don't see any non-reserved
> fields that span an 8-bit boundary, so you can probably rearrange the bits
> to make it work, but generally speaking it's better to not rely on how the
> compiler lays out bit fields.
>
>         Arnd

Agreed.
Will fix and submit a new series.

Thanks,
Sunil.