linux-kernel - Re: [PATCH] clk: tegra: fix SMP build

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Date:   Wed, 12 Dec 2018 14:31:27 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Stephen Boyd <sboyd@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Michael Turquette <mturquette@...libre.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Prashant Gaikwad <pgaikwad@...dia.com>,
        Dmitry Osipenko <digetx@...il.com>,
        Aapo Vienamo <avienamo@...dia.com>, linux-clk@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: tegra: fix SMP build

On Wed, Dec 12, 2018 at 11:47:32AM +0000, Jon Hunter wrote:
> 
> On 11/12/2018 17:21, Stephen Boyd wrote:
> > Quoting Arnd Bergmann (2018-12-11 06:35:07)
> >> When CONFIG_SMP is disabled, the tegra clk driver now fails to build:
> >>
> >> drivers/clk/tegra/clk-tegra30.c: In function 'tegra30_cpu_rail_off_ready':
> >> drivers/clk/tegra/clk-tegra30.c:1151:19: error: implicit declaration of function 'tegra_pmc_cpu_is_powered'; did you mean 'tegra_powergate_is_powered'? [-Werror=implicit-function-declaration]
> >>   cpu_pwr_status = tegra_pmc_cpu_is_powered(1) ||
> >>
> >> I don't know if tegra works without CONFIG_SMP, but we can get it to
> >> build by making the calls conditional, and removing the pointless
> >> ifdef around the declaration. The assumption now is that in a
> >> non-SMP system, the secondary CPUs are always disabled.
> >>
> >> Fixes: 61866523ed6e ("clk: tegra30: Use Tegra CPU powergate helper function")
> >> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> >> ---
> >> Not sure if this is the best solution. If you think it's not, please
> >> submit a different fix.
> > 
> > Hmm.. Is there any reason why the implementation of
> > tegra_pmc_cpu_is_powered() is under an ifdef CONFIG_SMP? I'd rather not
> > have to think about SMP or not in this clk code and have the
> > tegra_pmc_cpu_is_powered() function do the UP vs SMP code optimization.
> 
> Not that I know of. I just think that the function should/would not be
> used for non-SMP.
> 
> I was actually thinking that we could just leave the clk code as it is
> and simply drop the CONFIG_SMP from pmc.h. That would be fine with me.

Yeah, I'd be fine keeping that code around whether or not we enable SMP.
Chances are people won't disable it anyway. If they do, then most likely
only for testing purposes, in which case I'm sure they won't mind the
extra couple of bytes.

I think if we remove CONFIG_SMP from pmc.h we also need to remove it
from drivers/soc/tegra/pmc.c to make sure these functions are available,
otherwise we'll likely run into linker errors.

Jon, is that something I can interest you in? If not, I can easily do
that myself.

Thierry

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