From: Youngmin Nam <youngmin.nam@samsung.com>
To: krzysztof.kozlowski@canonical.com, will@kernel.org,
mark.rutland@arm.com, daniel.lezcano@linaro.org
Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-samsung-soc@vger.kernel.org, pullip.cho@samsung.com,
hoony.yu@samsung.com, hajun.sung@samsung.com,
myung-su.cha@samsung.com, kgene@kernel.org
Subject: Re: [PATCH v1 1/2] clocksource/drivers/exynos_mct_v2: introduce Exynos MCT version 2 driver for next Exynos SoC
Date: Wed, 27 Oct 2021 10:38:37 +0900 [thread overview]
Message-ID: <20211027013709.GA17353@perf> (raw)
In-Reply-To: <cb5bd5a3-1c23-0dc5-9f77-112befd7269c@canonical.com>
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On Tue, Oct 26, 2021 at 01:00:51PM +0200, Krzysztof Kozlowski wrote:
> On 26/10/2021 12:45, Youngmin Nam wrote:
> > On Tue, Oct 26, 2021 at 09:10:28AM +0200, Krzysztof Kozlowski wrote:
> >> On 26/10/2021 03:47, Youngmin Nam wrote:
> >>>> If everyone added a new driver to avoid integrating with existing code,
> >>>> we would have huge kernel with thousands of duplicated solutions. The
> >>>> kernel also would be unmaintained.
> >>>>
> >>>> Such arguments were brought before several times - "I don't want to
> >>>> integrating with existing code", "My use case is different", "I would
> >>>> need to test the other cases", "It's complicated for me".
> >>>>
> >>>> Instead of pushing a new vendor driver you should integrate it with
> >>>> existing code.
> >>>>
> >>> Let me ask you one question.
> >>> If we maintain as one driver, how can people who don't have the new MCT test the new driver?
> >>
> >> I assume you talk about a case when someone else later changes something
> >> in the driver. Such person doesn't necessarily have to test it. The same
> >> as in all other cases (Exynos MCT is not special here): just ask for
> >> testing on platform one doesn't have.
> >>
> >> Even if you submit this as separate driver, there is the exact same
> >> problem. People will change the MCTv2 driver without access to hardware.
> >>
> > Yes, I can test the new MCT driver if someone ask for testing after modifying the new driver.
> > But in this case, we don't need to test the previous MCT driver. We have only to test the new MCT driver.
>
> Like with everything in Linux kernel. We merge instead of duplicate.
> It's not an argument.
>
> >> None of these differ for Exynos MCT from other drivers, e.g. mentioned
> >> Samsung PMIC drivers, recently modified (by Will and Sam) the SoC clock
> >> drivers or the ChipID drivers (changed by Chanho).
> > From HW point of view, the previous MCT is almost 10-year-old IP without any major change and
> > it will not be used on next new Exynos SoC.
> > MCTv2 is the totally newly designed IP and it will replace the Exynos system timer.
> > Device driver would be dependent with H/W. We are going to apply a lot of changes for this new MCT.
> > For maintenance, I think we should separate the new MCT driver for maintenance.
> >
>
> There are several similarities which actually suggest that you
> exaggerate the differences.
>
> The number of interrupts is the same (4+8 in older one, 12 in new one...).
I didn't "exaggerate" at all.
The numer of interrups is the same. But their usage is completely different.
The type of each timer is different.
And previous MCT can only support upto 8 cores.
* MCTv1 (Let me call previous MCT as MCTv1)
- 4 global timer + 8 local timer
- Global timer and local timer are totally different.
- 4 global timer have only one 64bit FRC that serves as the "up-counter" with 4 "comparators"
- 8 local timer have 8 of 32bit FRC that serves as the "down-counter" without any "comparators".(just expire timer)
- local timer can be used as per-cpu event timer, so it can only support upto 8 cores.
* MCTv2
- There are no global timer and local timer anymore.
- 1 of 64bit FRC that serves as "up-counter" (just counter without "comparators")
- 12 comaprators (These are not "counter") can be used as per-cpu event timer so that it can support upto 12 cores.
- RTC source can be used as backup source.
> You assign the MCT priority also as higher than Architected Timer
> (+Cc Will and Mark - is it ok for you?)
> evt->rating = 500; /* use value higher than ARM arch timer *
>
Yes, this is absolutely correct on event timer.
We cannot use arm arch timer which is operating based on PPI as per-cpu event timer because of poewr mode.
We have to use SPI for per-cpu timer interrupt. (This is the same in all Exynos platform)
> All these point that block is not different. Again, let me repeat, we
> support old Samsung PMICs with new Samsung PMICs in one driver. Even
> though the "old one" won't be changed, as you mentioned here. The same
> Samsung SoC clock drivers are used for old Exynos and for new ones...
> Similarly to pinctrl drivers. The same ChipId.
>
> Everywhere we follow the same concept of unification instead of
> duplication. Maybe Exynos MCT timer is an exception but you did not
> provide any arguments supporting this. Why Exynos MCTv2 should be
> treated differently than Exynos850 clocks, chipid, pinctrl and other blocks?
>
If MCTv2 has only changes in register layout, I can consider merging work.
But this is not that case.
You gave a example with PMIC, SoC clock, Pinctrl, ChipId.
These H/W IP have only changes in register layout which came from difference of each SoC.
Were these H/W IP version changed?
Were these H/W IP control method changed ?
No. It only has minor chagnes not major changes.
* PMIC - controls the PMIC reigster with I2C interface regarding their SoC usecase.
- there is no changes on H/W control method itself.
* SoC Clock - changes only in register layout regarding SoC
- Clock control method still the same.
* Pinctrl - changes only in gpio pin register layout (pin number, pin type, pin map..) regarding SoC.
- Is there any changes on control method ?
* Chipid - This is very simple H/W IP. It only supports unique chip id value with read-only register.
- It really only have changes in register layout.
MCTv2 is different.
Not only register layout but also it's control method has to be changed regarding H/W difference.
> Daniel,
> Any preferences from you? Integrating MCT into existing driver (thus
> growing it) or having a new one?
>
> Best regards,
> Krzysztof
>
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next prev parent reply other threads:[~2021-10-27 1:11 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20211021055104epcas2p4bd5278e58860af8c136a850c0f080087@epcas2p4.samsung.com>
2021-10-21 6:18 ` [PATCH v1 0/2] Indroduce Exynos Multi Core Timer version 2 Youngmin Nam
[not found] ` <CGME20211021055112epcas2p278145beb21cd6cc4217813a41c1e1407@epcas2p2.samsung.com>
2021-10-21 6:18 ` [PATCH v1 1/2] clocksource/drivers/exynos_mct_v2: introduce Exynos MCT version 2 driver for next Exynos SoC Youngmin Nam
2021-10-21 6:18 ` Krzysztof Kozlowski
2021-10-21 8:26 ` Youngmin Nam
2021-10-21 8:07 ` Krzysztof Kozlowski
2021-10-22 4:21 ` Youngmin Nam
2021-10-25 8:18 ` Krzysztof Kozlowski
2021-10-26 1:47 ` Youngmin Nam
2021-10-26 7:10 ` Krzysztof Kozlowski
2021-10-26 10:45 ` Youngmin Nam
2021-10-26 11:00 ` Krzysztof Kozlowski
[not found] ` <CGME20211027011125epcas2p2916524051416ede854b750c91a19073b@epcas2p2.samsung.com>
2021-10-27 1:38 ` Youngmin Nam [this message]
2021-10-27 6:39 ` Krzysztof Kozlowski
2021-11-01 6:04 ` Youngmin Nam
2021-10-27 7:34 ` Will Deacon
2021-10-29 3:54 ` Youngmin Nam
2021-10-26 11:00 ` Krzysztof Kozlowski
2021-10-27 8:38 ` Krzysztof Kozlowski
2021-11-01 5:25 ` Youngmin Nam
[not found] ` <CGME20211021055115epcas2p158fbf3ac61d3deeb5995bd100d7edef1@epcas2p1.samsung.com>
2021-10-21 6:18 ` [PATCH v1 2/2] dt-bindings: timer: samsung,s5e99xx-mct: Document s5e99xx-mct bindings Youngmin Nam
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