linux-kernel - Re: [PATCH 0/6] 32-bit Meson: add the ARM TWD and Global Timers

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Date:   Tue, 04 Dec 2018 16:51:33 -0800
From:   Kevin Hilman <khilman@...libre.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        carlo@...one.org, linux-amlogic@...ts.infradead.org
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: Re: [PATCH 0/6] 32-bit Meson: add the ARM TWD and Global Timers

Martin Blumenstingl <martin.blumenstingl@...glemail.com> writes:

> The 32-bit Meson SoCs use Cortex-A9 or Cortex-A5 cores. These come
> with the ARM TWD ("Timer Watchdog") which contains a timer and a
> watchdog as well as the ARM Global Timer.
>
> This enables the corresponding configs for the 32-bit Meson target.
> Additionally this adds and enables the ARM TWD timer. The Global
> Timer is added but currently disabled because it's clock input is
> the PERIPH clock which is derived from the CPU clock. Thus the rate
> of the PERIPH clock will change when changing the CPU frequency.
> Unfortunately the Global Timer driver doesn't handle clocks with
> changing rates yet (unlike the TWD timer), thus we keep it disabled
> for now.
>
> The whole series is inspired by an almost 3 year old patch from
> Carlo: [0]
>
>
> Dependencies:
> - I build this on top of my other series "ARM: dts: meson: add the
>   timer interrupts and clocks" from [1]
> - CLKID_PERIPH requires updated clock driver headers. Neil provided
>   a tag which includes the updated headers: [2]

I pulled this branch into v4.21/dt

> - There is no runtime dependency on the PERIPH clock as we don't
>   have CPU frequency scaling support enabled yet. In case the TWD
>   timer driver can't find the clock it falls back to auto-detecting
>   the clock rate at boot time. This is safe as long as we don't have
>   .dts patches in place which allow changing the CPU clock rate. Once
>   we enable CPU frequency scaling support for the PERIPH clock becomes
>   mandatory so the TWD timer driver knows about changes to the PERIPH
>   clock (which is derived from the CPU clock).
>
>
> [0] https://patchwork.kernel.org/patch/7797581/
> [1] https://patchwork.kernel.org/cover/10687005/
> [2] http://lists.infradead.org/pipermail/linux-amlogic/2018-November/009136.html
>
>
> Martin Blumenstingl (6):
>   ARM: meson: select HAVE_ARM_TWD and ARM_GLOBAL_TIMER

Applied to v4.21/defconfig

>   ARM: dts: meson: group the Cortex-A5 / Cortex-A9 peripherals
>   ARM: dts: meson8: add the ARM TWD timer
>   ARM: dts: meson8: add the Cortex-A9 global timer
>   ARM: dts: meson8b: add the ARM TWD timer
>   ARM: dts: meson8b: add the Cortex-A5 global timer

Applied to v4.21/dt

Kevin