linux-kernel - Re: [PATCH AUTOSEL 5.4 095/108] ARM: shmobile: Enable ARM_GLOBAL

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Message-ID: <CAMuHMdVrp25m_SDKSC=ntNWxsumcw4JKvHNDeFZT_JnpfQmCxg@mail.gmail.com>
Date:   Sun, 12 Apr 2020 10:44:01 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Sasha Levin <sashal@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH AUTOSEL 5.4 095/108] ARM: shmobile: Enable
 ARM_GLOBAL_TIMER on Cortex-A9 MPCore SoCs

Hi Sasha,

On Sun, Apr 12, 2020 at 1:11 AM Sasha Levin <sashal@...nel.org> wrote:
> From: Geert Uytterhoeven <geert+renesas@...der.be>
>
> [ Upstream commit 408324a3c5383716939eea8096a0f999a0665f7e ]
>
> SH-Mobile AG5 and R-Car H1 SoCs are based on the Cortex-A9 MPCore, which
> includes a global timer.
>
> Enable the ARM global timer on these SoCs, which will be used for:
>   - the scheduler clock, improving scheduler accuracy from 10 ms to 3 or
>     4 ns,
>   - delay loops, allowing removal of calls to shmobile_init_delay() from
>     the corresponding machine vectors.
>
> Note that when using an old DTB lacking the global timer, the kernel
> will still work.  However, loops-per-jiffies will no longer be preset,
> and the delay loop will need to be calibrated during boot.

I.e. to avoid this delay, this patch is best backported after backporting
8443ffd1bbd5be74 ("ARM: dts: r8a7779: Add device node for ARM global timer"),
df1a0aac0a533e6f ("ARM: dts: sh73a0: Add device node for ARM global timer").

While the former has been backported to v5.[45]-stable, the latter hasn't,
probably because it depends on
61b58e3f6e518c51 ("ARM: dts: sh73a0: Rename twd clock to periph clock")

So please backport the last two commits first.
Thanks!

> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Link: https://lore.kernel.org/r/20191211135222.26770-5-geert+renesas@glider.be
> Signed-off-by: Sasha Levin <sashal@...nel.org>

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