Messages in this thread | | | From | Walter Chang (張維哲) <> | Subject | Re: [PATCH v2 4/4] clocksource/drivers/timer-mediatek: Make timer-mediatek become loadable module | Date | Wed, 29 Mar 2023 06:22:57 +0000 |
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On Thu, 2023-02-16 at 12:36 +0100, AngeloGioacchino Del Regno wrote: > Il 16/02/23 12:23, Matthias Brugger ha scritto: > > > > > > On 16/02/2023 11:22, AngeloGioacchino Del Regno wrote: > > > Il 15/02/23 15:46, Sudeep Holla ha scritto: > > > > On Wed, Feb 15, 2023 at 02:30:51PM +0100, AngeloGioacchino Del > > > > Regno wrote: > > > > > > > > > > Both. I mean that these platforms do have architected timers, > > > > > but they are stopped > > > > > before the bootloader jumps to the kernel, or they are never > > > > > started at all. > > > > > > > > > > Please refer to: > > > > > > > > > > https://urldefense.com/v3/__https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/clocksource/timer-mediatek.c?h=next-20230215&id=327e93cf9a59b0d04eb3a31a7fdbf0f11cf13ecb__;!!CTRNKA9wMg0ARbw!jOX04TQn1HXcKOdzAiK3ZlqsSE3j3p6Zo-Cajr0khXC9ANlbkl8kQrUgx6wadR8b_46o9J0SbJgjhoS03rQ7somJfA5Z9L6G_g$ > > > > > > > > > > > > > > > For a nice explanation. > > > > > > > > > > > > > Thanks for that. Well then I see no point in making these > > > > modules if you > > > > can't have generic Image that boots on all the platform. I now > > > > tend to think > > > > that these are made modules just because GKI demands and it > > > > *might* work > > > > on one or 2 platforms. One we move this as modules, how will be > > > > know the > > > > Image without these timers or with them built as modules will > > > > boot or not > > > > on a given mediatek platform. Sorry, I initially saw some point > > > > in making > > > > these timers as modules but if they are required for boot on > > > > some systems > > > > then I see no point. So if that is the case, NACK for these as > > > > it just > > > > creates more confusion after these are merged as why some > > > > Images or > > > > even why defconfig image(if we push the config change as well) > > > > is not > > > > booting on these platforms. > > > > > > > > It is no longer just for system timer useful in low power CPU > > > > idle states > > > > as I initial thought. > > > > > > > > > > I think that there is still a point in modularization for this > > > driver and I > > > can propose a rather simple solution, even though this may add > > > some, rather > > > little, code duplication to the mix. > > > > > > The platforms that I've described (like mt6795) need the system > > > timer to be > > > initialized as early as possible - that's true - but that timer > > > is always > > > "CPUXGPT". > > > > > > On those platforms, you *still* have multiple timers: > > > - CPUX (short for cpuxgpt), used only as system timer; > > > - SYST, as another system timer implementation (additional > > > timers) but > > > those are always initialized (AFAIK) from the bootloader > > > before booting; > > > - GPT (General Purpose Timer). > > > > > > On one SoC, you may have: > > > - CPUX *and* SYST > > > - CPUX *and* GPT > > > - CPUX *and* SYST *and* GPT > > > > > > ... where the only one that is boot critical and needs to be > > > initialized early > > > is always only CPUX. > > > > > > Hence this proposal: to still allow modularization of timers on > > > MediaTek platforms, > > > we could eventually split the CPUX as a separated driver that > > > *cannot be*, due to > > > the previously explained constraints, compiled as module, hence > > > always built-in, > > > from a timer-mediatek driver that could be a module and capable > > > of handling only > > > SYST and GPT timers. > > > > > > In that case, we'd hence have... > > > - timer-mediatek-cpux.o (bool) > > > - timer-mediatek.c (tristate) > > > > > > Counting that the CPUX timers are actually even using different > > > `tick_resume` > > > and `set_state_shutdown` callbacks (doing only a IRQ > > > clear/restore and nothing > > > else), the amount of duplication would be .. well, again, > > > minimal, but then > > > this means that timer-mediatek-cpux would be `default y if > > > ARCH_MEDIATEK`, or > > > even selected by ARCH_MEDIATEK itself. > > > > > > If you think that this could be a good solution, I can send a > > > "fast" patch to > > > split it out, preparing the ground for the people doing this > > > module work. > > > > > > Any considerations? > > > > > > > I think your proposal sounds acceptable, but we would need to make > > sure that all > > SoCs can boot with the CPUX driver. I'm aware of some armv7 SoCs > > that use a kind of > > hack to enable the architecture timer [1]. This, for one part, > > should be moved to > > CPUX, if possible. For the other part it makes me wonder if really > > all supported > > MediaTek platforms will boot with SYST/GPT being a module. I think > > we will need > > some effort from the community to test that. > > > > So as a resume, yes I think your approach is feasible but we should > > collect > > tested-by tags before merging it. > > > > Regards, > > Matthias > > > > > > [1] > > https://urldefense.com/v3/__https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/mach-mediatek/mediatek.c?h=v6.2-rc8*n16__;Iw!!CTRNKA9wMg0ARbw!jOX04TQn1HXcKOdzAiK3ZlqsSE3j3p6Zo-Cajr0khXC9ANlbkl8kQrUgx6wadR8b_46o9J0SbJgjhoS03rQ7somJfA5mnCQ6Fw$ > > > > Right. I completely forgot about those platforms, even though my > intention was > to actually try and migrate them once the CPUX was picked. My bad. > > Well, I think that this module conversion will take quite a while, so > there > should be no need to rush... I'll send a series later with the split > *and* a > conversion of those platforms, so that we will see a removal of that > mediatek_timer_init() function. > > Some encouraging words ahead: I'm totally confident that the > conversion will > Just Work, because the MT6795 SoC had the same handling for CPUXGPT > as the > older MT6589/7623/8127/8135... as that SoC had two implementations > initially, > one as ARM, one as ARM64. > > Whatever - let's see what I can come up with, then. > > Cheers, > Angelo
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/
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