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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Sat, 29 Dec 2018 23:36:49 +0100
Message-ID: <CAK8P3a2p91XJfJuSCZqRLRgC-aP3LR1tMK2DDxTiSuD8_FOg8Q@mail.gmail.com>
Subject: Re: [PATCH v8 24/25] powerpc: Adopt nvram module for PPC64
To:     Finn Thain <fthain@telegraphics.com.au>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-m68k <linux-m68k@lists.linux-m68k.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
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On Wed, Dec 26, 2018 at 1:43 AM Finn Thain <fthain@telegraphics.com.au> wrote:

> +static ssize_t ppc_nvram_get_size(void)
> +{
> +       if (ppc_md.nvram_size)
> +               return ppc_md.nvram_size();
> +       return -ENODEV;
> +}

> +const struct nvram_ops arch_nvram_ops = {
> +       .read           = ppc_nvram_read,
> +       .write          = ppc_nvram_write,
> +       .get_size       = ppc_nvram_get_size,
> +       .sync           = ppc_nvram_sync,
> +};

Coming back to this after my comment on the m68k side, I notice that
there is now a double indirection through function pointers. Have you
considered completely removing the operations from ppc_md instead
by having multiple copies of nvram_ops?

With the current method, it does seem odd to have a single
per-architecture instance of the exported structure containing
function pointers. This doesn't give us the flexibility of having
multiple copies in the kernel the way that ppc_md does, but it adds
overhead compared to simply exporting the functions directly.

       Arnd