linux-kernel - Re: [PATCH v2 4/4] clocksource/drivers/timer-mediatek: Make timer-mediatek become loadable module

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Date:   Mon, 10 Apr 2023 06:58:00 +0000
From:   Walter Chang (張維哲) 
        <Walter.Chang@...iatek.com>
To:     "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "sudeep.holla@....com" <sudeep.holla@....com>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "jstultz@...gle.com" <jstultz@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "krzysztof.kozlowski@...aro.org" <krzysztof.kozlowski@...aro.org>,
        Chun-Hung Wu (巫駿宏) 
        <Chun-hung.Wu@...iatek.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Stanley Chu (朱原陞) 
        <stanley.chu@...iatek.com>,
        "macro@...am.me.uk" <macro@...am.me.uk>,
        Freddy Hsin (辛恒豐) 
        <Freddy.Hsin@...iatek.com>
Subject: Re: [PATCH v2 4/4] clocksource/drivers/timer-mediatek: Make
 timer-mediatek become loadable module

On Wed, 2023-03-29 at 14:22 +0800, Walter.Chang wrote:
> First, I'd like to thank Angelo for assisting us in spliting out the
> CPUX driver [1], allowing this driver to become a module that can be
> loaded when needed.
> 
> In response to Matthias's concern about whether SYST/GPT on the old
> MediaTek platforms can boot properly with the loadable module, I
> recently conducted a few tests and found that both hardwares are
> capable of booting normally with this loadable module.
> 
> For my experiments, I used MT6768 with this patch:
> 
> 1. When the module was not loaded or load the module but the
> corresponding compatible property was not specified in the dts, the
> following results were obtained:
> 
> # cat /proc/timer_list | grep "Broadcast device" -A 15
> Broadcast device
> Clock Event Device: bc_hrtimer
>  max_delta_ns:   9223372036854775807
>  min_delta_ns:   1
>  mult:           1
>  shift:          0
>  mode:           3
>  next_event:     490204000000 nsecs
>  set_next_event: <0000000000000000>
>  shutdown: bc_shutdown.cfi_jt
>  event_handler:  tick_handle_oneshot_broadcast.cfi_jt
>  retries:        0
> 
> tick_broadcast_mask: ff
> tick_broadcast_oneshot_mask: 7e
> 
> The built-in `bc_hrtimer` was used as the broadcast device, whereby
> one
> CPU was kept awake to wake up the other CPUs. As a result, one CPU
> could not enter the idle state.
> 
> 2. When the module was loaded and the GPT compatible property was
> specified in the dts:
> 
> # cat /proc/timer_list | grep "Broadcast device" -A 17
> Broadcast device
> Clock Event Device: mtk-clkevt
>  max_delta_ns:   330382104634
>  min_delta_ns:   1000
>  mult:           27917287
>  shift:          31
>  mode:           3
>  next_event:     1483221016462 nsecs
>  set_next_event: mtk_gpt_clkevt_next_event.cfi_jt
>  shutdown: mtk_gpt_clkevt_shutdown.cfi_jt
>  periodic: mtk_gpt_clkevt_set_periodic.cfi_jt
>  oneshot:  mtk_gpt_clkevt_shutdown.cfi_jt
>  resume:   mtk_gpt_clkevt_shutdown.cfi_jt
>  event_handler:  tick_handle_oneshot_broadcast.cfi_jt
>  retries:        17
> 
> tick_broadcast_mask: ff
> tick_broadcast_oneshot_mask: bf
> 
> 3. When the module was loaded and the SYST compatible property was
> specified in the dts:
> 
> # cat /proc/timer_list | grep "Broadcast device" -A 17
> Broadcast device
> Clock Event Device: mtk-clkevt
>  max_delta_ns:   330382104634
>  min_delta_ns:   1000
>  mult:           27917287
>  shift:          31
>  mode:           3
>  next_event:     132252000000 nsecs
>  set_next_event: mtk_syst_clkevt_next_event.cfi_jt
>  shutdown: mtk_syst_clkevt_shutdown.cfi_jt
>  oneshot:  mtk_syst_clkevt_oneshot.cfi_jt
>  resume:   mtk_syst_clkevt_resume.cfi_jt
>  event_handler:  tick_handle_oneshot_broadcast.cfi_jt
>  retries:        8
> 
> tick_broadcast_mask: ff
> tick_broadcast_oneshot_mask: 3f
> 
> These two experiments show that SYST/GPT on the old MediaTek
> platforms
> can also work properly with the loadable module, and will not cause
> any
> booting issues. Therefore, making timer-mediatek.c driver into a
> loadable module is feasible.
> 
> Thanks,
> Walter Chang
> 
> [1] 
> 
https://lore.kernel.org/lkml/20230309103913.116775-1-angelogioacchino.delregno@collabora.com/

Gentle ping.

Thanks,
Walter Chang