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

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Message-ID: <20200417171802.GV1068@sasha-vm>
Date:   Fri, 17 Apr 2020 13:18:02 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.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

On Sun, Apr 12, 2020 at 10:44:01AM +0200, Geert Uytterhoeven wrote:
>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.

Done, thanks!

-- 
Thanks,
Sasha