Date:   Wed, 15 Feb 2023 13:18:49 +0000
From:   Sudeep Holla <sudeep.holla@arm.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
Cc:     walter.chang@mediatek.com,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Sudeep Holla <sudeep.holla@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        "Maciej W . Rozycki" <macro@orcam.me.uk>,
        John Stultz <jstultz@google.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        wsd_upstream@mediatek.com, stanley.chu@mediatek.com,
        Chun-hung.Wu@mediatek.com, Freddy.Hsin@mediatek.com,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org
Subject: Re: [PATCH v2 4/4] clocksource/drivers/timer-mediatek: Make
 timer-mediatek become loadable module
Message-ID: <20230215131849.mcgz53jf24atialp@bogus>
References: <20230214105412.5856-1-walter.chang@mediatek.com>
 <20230214105412.5856-5-walter.chang@mediatek.com>
 <20230214222021.k3tsfwezhnh7tdlx@bogus>
 <996b4e61-8486-d939-7367-1240b3c5c5fa@collabora.com>
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On Wed, Feb 15, 2023 at 01:43:19PM +0100, AngeloGioacchino Del Regno wrote:
> Il 14/02/23 23:20, Sudeep Holla ha scritto:
> > On Tue, Feb 14, 2023 at 06:53:14PM +0800, walter.chang@mediatek.com wrote:
> > > From: Chun-Hung Wu <chun-hung.wu@mediatek.com>
> > > 
> > > Make the timer-mediatek driver which can register
> > > an always-on timer as tick_broadcast_device on
> > > MediaTek SoCs become loadable module in GKI.
> > > 
> > > Signed-off-by: Chun-Hung Wu <chun-hung.wu@mediatek.com>
> > > ---
> > >   drivers/clocksource/Kconfig          |  2 +-
> > >   drivers/clocksource/timer-mediatek.c | 43 ++++++++++++++++++++++++++++
> > >   2 files changed, 44 insertions(+), 1 deletion(-)
> > 
> > [...]
> > 
> > > diff --git a/drivers/clocksource/timer-mediatek.c b/drivers/clocksource/timer-mediatek.c
> > > index d5b29fd03ca2..3358758ea694 100644
> > > --- a/drivers/clocksource/timer-mediatek.c
> > > +++ b/drivers/clocksource/timer-mediatek.c
> > 
> > [...]
> > 
> > > +static const struct of_device_id mtk_timer_match_table[] = {
> > > +	{
> > > +		.compatible = "mediatek,mt6577-timer",
> > > +		.data = mtk_gpt_init,
> > > +	},
> > > +	{
> > > +		.compatible = "mediatek,mt6765-timer",
> > > +		.data = mtk_syst_init,
> > > +	},
> > > +	{
> > > +		.compatible = "mediatek,mt6795-systimer",
> > > +		.data = mtk_cpux_init,
> > > +	},
> > > +	{}
> > > +};
> > > +
> > > +static struct platform_driver mtk_timer_driver = {
> > > +	.probe = mtk_timer_probe,
> > > +	.driver = {
> > > +		.name = "mtk-timer",
> > > +		.of_match_table = mtk_timer_match_table,
> > > +	},
> > > +};
> > > +module_platform_driver(mtk_timer_driver);
> > > +
> > > +MODULE_DESCRIPTION("MediaTek Module Timer driver");
> > > +MODULE_LICENSE("GPL v2");
> > > +#else
> > >   TIMER_OF_DECLARE(mtk_mt6577, "mediatek,mt6577-timer", mtk_gpt_init);
> > >   TIMER_OF_DECLARE(mtk_mt6765, "mediatek,mt6765-timer", mtk_syst_init);
> > >   TIMER_OF_DECLARE(mtk_mt6795, "mediatek,mt6795-systimer", mtk_cpux_init);
> >
> > Why do you need these ? If this driver can work as a module, it can be
> > built-in module and doesn't need to be initialised early using of_timer_init
> > (can't recall the exact name)
> >
>
> Some platforms need early initialization; this is seen on ones for which the
> bootloader does not initialize the "CPUXGPT" timer, which is used as the ARM
> arch timer. (No, on those platforms you can't upgrade the bootloader, as it's
> signed with a OEM key which is not obtainable, and signature verified earlier
> in the bootchain).
>

Is this arm32 or arm64 platform? Do you mean that these platforms don't have
working architected timers ?

Quick grep suggests the below list of platforms/SoC:

 | arch/arm64/boot/dts/mediatek/mt6795.dtsi
 | arch/arm64/boot/dts/mediatek/mt8173.dtsi
 | arch/arm64/boot/dts/mediatek/mt8183.dtsi
 | arch/arm64/boot/dts/mediatek/mt8186.dtsi
 | arch/arm64/boot/dts/mediatek/mt8192.dtsi
 | arch/arm64/boot/dts/mediatek/mt8195.dtsi
 | arch/arm64/boot/dts/mediatek/mt8516.dtsi
 | arch/arm/boot/dts/mt7623.dtsi
 | arch/arm/boot/dts/mt7629.dtsi
 | arch/arm/boot/dts/mt8127.dtsi
 | arch/arm/boot/dts/mt8135.dtsi

All the above has architected timers and can have the other timer initialised
at module_initcall level.

 | arch/arm/boot/dts/mt2701.dtsi
 | arch/arm/boot/dts/mt6580.dtsi
 | arch/arm/boot/dts/mt6582.dtsi
 | arch/arm/boot/dts/mt6589.dtsi
 | arch/arm/boot/dts/mt6592.dtsi

The above ones have cortex-a7 but still don't have architected timers listed
in the DT. Anyways all use "mediatek,mt6577-timer", so except that other
2 can be dropped from the else and force them to be initialised later.

> As a matter of fact (and somehow obvious), on those platforms (for example,
> MT6795.. but many other as well, really), you *need* this driver to be
> built-in and, well, initialize the CPUX timer as early as possible :-)
>

Built-in is not a problem, you can still remove TIMER_OF_DECLARE as
the initialisation happens later at module_initcall level.

-- 
Regards,
Sudeep