linux-kernel - Re: [PATCH V2] staging: fieldbus: anybus-s: force endiannes annotation

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Message-ID: <CAGngYiVSg86X+jD+hgwwrOYX82Fu3OWSLygwGFzyc9wYq6AesQ@mail.gmail.com>
Date:   Tue, 30 Apr 2019 09:32:20 -0400
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Nicholas Mc Guire <der.herr@...r.at>,
        Nicholas Mc Guire <hofrat@...dl.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devel@...verdev.osuosl.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] staging: fieldbus: anybus-s: force endiannes annotation

On Tue, Apr 30, 2019 at 12:19 AM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> ... not that there's much sense keeping ->fieldbus_type in host-endian,
> while we are at it.

Interesting! Suppose we make device->fieldbus_type bus-endian.
Then the endinan-ness conversion either needs to happen in
bus_match() (and we'd have to convert endianness each time
this function is called).
Or, we make driver->fieldbus_type bus-endian also, then there
is no need for conversion... but the driver writer has to remember
to specify this in bus endianness:

static struct anybuss_client_driver profinet_driver = {
        .probe = ...,
        .fieldbus_type = endian convert?? (0x0089),
};

Which pushes bus implementation details onto the
client driver writer? Also, how to convert a constant
to a specific endianness in a static initializer?

You never make a remark without good reason, so what
am I overlooking?