Messages in this thread | | | Date | Thu, 16 Feb 2023 12:23:06 +0100 | From | Matthias Brugger <> | Subject | Re: [PATCH v2 4/4] clocksource/drivers/timer-mediatek: Make timer-mediatek become loadable module |
| |
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://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/clocksource/timer-mediatek.c?h=next-20230215&id=327e93cf9a59b0d04eb3a31a7fdbf0f11cf13ecb >>> >>> 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://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/mach-mediatek/mediatek.c?h=v6.2-rc8#n16
| |