linux-kernel - Re: [PATCH 2/2] spi: rpc-if: Remove CONFIG_PM

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Date:   Tue, 5 Jan 2021 08:37:58 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     Mark Brown <broonie@...nel.org>,
        "Lad, Prabhakar" <prabhakar.csengg@...il.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Jiri Kosina <trivial@...nel.org>,
        Sergei Shtylyov <sergei.shtylyov@...il.com>,
        linux-spi <linux-spi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Chris Brandt <Chris.Brandt@...esas.com>
Subject: Re: [PATCH 2/2] spi: rpc-if: Remove CONFIG_PM_SLEEP ifdefery

Hi Pavel,

On Tue, Jan 5, 2021 at 12:40 AM Pavel Machek <pavel@...x.de> wrote:
> > > > >                 .name   = "rpc-if-spi",
> > > > > -               .pm     = DEV_PM_OPS,
> > > > > +               .pm     = &rpcif_spi_pm_ops,
> >
> > > > You're aware rpcif_spi_pm_ops is now always referenced and thus emitted,
> > > > increasing kernel size by 92 bytes if CONFIG_PM_SLEEP=n?
> > > > This may matter for RZ/A SoCs running from internal SRAM.
> >
> > > Hmm didn't realise this would be an issue on RZ/A.
> >
> > > Mark, could you please drop this patch from your branch.
> >
> > Please send an incremental patch with an appropriate changelog.
>
> Let's fix this properly. I'm pretty sure we have some macros that can
> solve this without re-introducing the ifdefs...

There's pm_ptr(), but it uses CONFIG_PM as a selector, not CONFIG_PM_SLEEP.

> (Besides... 92 bytes. How big is kernel these days? 4MB? More? How
> much SRAM do you have?)

92 bytes is indeed not much (on 64-bit it would be doubled).
Still, it's good to make people think about innocent looking changes,
once in a while.

RZ/A1H and RZ/A1M have 10 resp. 5 MiB of SRAM.
RZ/A2 has 4 MiB SRAM, which is sufficient to run Linux when used with
XIP (requires a one-line Kconfig change rmk has been vetoing for years).

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds