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From: Sam Protsenko <semen.protsenko@linaro.org>
To: Marc Zyngier <maz@kernel.org>
Cc: Sylwester Nawrocki <s.nawrocki@samsung.com>,
	Chanwoo Choi <cw00.choi@samsung.com>,
	Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Tomasz Figa <tomasz.figa@gmail.com>,
	Rob Herring <robh+dt@kernel.org>, Stephen Boyd <sboyd@kernel.org>,
	Michael Turquette <mturquette@baylibre.com>,
	Jiri Slaby <jirislaby@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Charles Keepax <ckeepax@opensource.wolfsonmicro.com>,
	Ryu Euiyoul <ryu.real@samsung.com>,
	Tom Gall <tom.gall@linaro.org>,
	Sumit Semwal <sumit.semwal@linaro.org>,
	John Stultz <john.stultz@linaro.org>,
	Amit Pundir <amit.pundir@linaro.org>,
	devicetree <devicetree@vger.kernel.org>,
	linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>,
	linux-clk <linux-clk@vger.kernel.org>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux Samsung SOC <linux-samsung-soc@vger.kernel.org>,
	"open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>
Subject: Re: [PATCH 12/12] arm64: dts: exynos: Add Exynos850 SoC support
Date: Wed, 4 Aug 2021 21:37:24 +0300	[thread overview]
Message-ID: <CAPLW+4mMF9B2BiY2hTgHz5=DNbDJZ7TDzt=Xefb5tDKwQhpEew@mail.gmail.com> (raw)
In-Reply-To: <87k0l1w8y5.wl-maz@kernel.org>

On Wed, 4 Aug 2021 at 18:01, Marc Zyngier <maz@kernel.org> wrote:
>
> On Wed, 04 Aug 2021 15:39:38 +0100,
> Sam Protsenko <semen.protsenko@linaro.org> wrote:
>
> > > You are also missing the hypervisor virtual timer interrupt.
> > >
> >
> > Checked SoC TRM, there is no PPI for hypervisor virtual timer
> > interrupt, and no mentioning of it at all. Likewise, I checked ARMv8
> > ARM and TRM, almost no description of it. Also, I checked other
> > platforms, and seems like everyone does the same (having only 4
> > interrupts). And I wasn't able to find any documentation on that, so I
> > guess I'll leave it as is, if you don't mind.
>
> I *do* mind, and other DTs being wrong isn't a good enough excuse! ;-)
>
> From the ARMv8 ARM (ARM DDI 0487G.b)
> <quote>
> D11.2.4 Timers
>
> In an implementation of the Generic Timer that includes EL3, if EL3
> can use AArch64, the following timers are implemented:
>
> * An EL1 physical timer, that:
>   - In Secure state, can be accessed from EL1.
>   - In Non-secure state, can be accessed from EL1 unless those
>     accesses are trapped to EL2.
>     When this timer can be accessed from EL1, an EL1 control
>     determines whether it can be accessed from EL0.
> * A Non-secure EL2 physical timer.
> * A Secure EL3 physical timer. An EL3 control determines whether this
>   register is accessible from Secure EL1.
> * An EL1 virtual timer.
> * When FEAT_VHE is implemented, a Non-secure EL2 virtual timer.
> * When FEAT_SEL2 is implemented, a Secure EL2 physical timer.
> * When FEAT_SEL2 is implemented, a Secure EL2 virtual timer.
> </quote>
>
> Cortex-A55 being an ARMv8.2 implementation, it has FEAT_VHE, and thus
> it does have a NS-EL2 virtual timer. This is further confirmed by the
> TRM which documents CNTHV*_EL2 as valid system registers[1].
>
> So the timer exists, the signal is routed out of the core, and it
> is likely that it is connected to the GIC.
>
> If the designers have omitted it, then it needs to be documented as
> such.
>

Ok, I've checked thoroughly all docs again, and it seems like there is
no dedicated PPI number for this "EL2 Hypervisor Virtual Timer" in
Exynos850 SoC. The timer instance itself might exist of course, but
interrupt line is probably wasn't connected to GIC by SoC designers,
at least it's not documented.

Moreover, from [1,2] it looks like if it were existing it would have
been PPI=12 (INTID=28). But in GIC-400 TRM this PPI is assigned to
"Legacy FIQ signal", and all there is no PPI for Hypervisor Virtual
Timer documented there as well. In Exynos850 TRM the source for this
PPI's interrupt source is marked as "-", which means it's not used.

So if you know something that I don't know -- please point me out the
doc where this PPI line is documented. Otherwise I can add the comment
to device tree, stating that this interrupt line is not present in
SoC's GIC, i.e. something like this:

8<------------------------------------------------------------------------------->8
    timer {
        compatible = "arm,armv8-timer";
        interrupts = <GIC_PPI 13 (GIC_CPU_MASK_SIMPLE(8) |
                      IRQ_TYPE_LEVEL_LOW)>,
                 <GIC_PPI 14 (GIC_CPU_MASK_SIMPLE(8) |
                      IRQ_TYPE_LEVEL_LOW)>,
                 <GIC_PPI 11 (GIC_CPU_MASK_SIMPLE(8) |
                      IRQ_TYPE_LEVEL_LOW)>,
                 <GIC_PPI 10 (GIC_CPU_MASK_SIMPLE(8) |
                      IRQ_TYPE_LEVEL_LOW)>;
        /* Hypervisor Virtual Timer PPI is not present in this SoC GIC */
    };
8<------------------------------------------------------------------------------->8

Is that ok with you?

[1] https://developer.arm.com/documentation/102379/0000/The-processor-timers?lang=en
[2] https://gem5.googlesource.com/public/gem5/+/refs/heads/master/src/arch/arm/fastmodel/CortexA76/FastModelCortexA76.py#150

> Thanks,
>
>         M.
>
> [1] https://developer.arm.com/documentation/100442/0100/register-descriptions/aarch64-system-registers/aarch64-architectural-system-register-summary
>
> --
> Without deviation from the norm, progress is not possible.

  reply	other threads:[~2021-08-04 18:37 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-30 14:49 [PATCH 00/12] Add minimal support for Exynos850 SoC Sam Protsenko
2021-07-30 14:49 ` [PATCH 01/12] pinctrl: samsung: Fix pinctrl bank pin count Sam Protsenko
2021-07-30 14:49 ` [PATCH 02/12] pinctrl: samsung: Add Exynos850 SoC specific data Sam Protsenko
2021-07-30 15:22   ` Krzysztof Kozlowski
2021-08-02 19:24     ` Sam Protsenko
2021-07-30 14:49 ` [PATCH 03/12] dt-bindings: pinctrl: samsung: Add Exynos850 doc Sam Protsenko
2021-07-30 15:24   ` Krzysztof Kozlowski
2021-07-30 19:31     ` Sam Protsenko
2021-07-30 14:49 ` [PATCH 04/12] tty: serial: samsung: Init USI to keep clocks running Sam Protsenko
2021-07-30 16:31   ` Krzysztof Kozlowski
2021-08-02 23:06     ` Sam Protsenko
2021-08-03  7:37       ` Krzysztof Kozlowski
2021-08-03 11:41         ` Sam Protsenko
2021-07-30 14:49 ` [PATCH 05/12] tty: serial: samsung: Fix driver data macros style Sam Protsenko
2021-07-30 16:34   ` Krzysztof Kozlowski
2021-07-30 14:49 ` [PATCH 06/12] tty: serial: samsung: Add Exynos850 SoC data Sam Protsenko
2021-07-30 15:05   ` Andy Shevchenko
2021-07-30 16:05   ` Krzysztof Kozlowski
2021-07-30 23:10     ` Sam Protsenko
2021-07-31  7:12       ` Krzysztof Kozlowski
2021-07-30 14:49 ` [PATCH 07/12] dt-bindings: serial: samsung: Add Exynos850 doc Sam Protsenko
2021-07-30 16:35   ` Krzysztof Kozlowski
2021-07-30 19:04     ` Sam Protsenko
2021-07-30 14:49 ` [PATCH 08/12] MAINTAINERS: Cover Samsung clock YAML bindings Sam Protsenko
2021-07-30 15:06   ` Andy Shevchenko
2021-07-30 15:25     ` Krzysztof Kozlowski
2021-07-30 17:32       ` Sam Protsenko
2021-07-30 14:49 ` [PATCH 09/12] dt-bindings: clock: Add bindings for Exynos850 clock controller Sam Protsenko
2021-07-30 15:43   ` Krzysztof Kozlowski
2021-08-03 11:55     ` Sam Protsenko
2021-07-30 22:28   ` Rob Herring
2021-07-30 14:49 ` [PATCH 10/12] clk: samsung: Add Exynos850 clock driver stub Sam Protsenko
2021-07-30 15:11   ` Andy Shevchenko
2021-07-30 17:24     ` Sam Protsenko
2021-07-30 14:49 ` [PATCH 11/12] dt-bindings: interrupt-controller: Add IRQ constants for Exynos850 Sam Protsenko
2021-07-31  8:45   ` Krzysztof Kozlowski
2021-08-03 12:58     ` Sam Protsenko
2021-07-30 14:49 ` [PATCH 12/12] arm64: dts: exynos: Add Exynos850 SoC support Sam Protsenko
2021-07-30 16:50   ` Marc Zyngier
2021-08-04 14:39     ` Sam Protsenko
2021-08-04 15:01       ` Marc Zyngier
2021-08-04 18:37         ` Sam Protsenko [this message]
2021-08-05  7:39           ` Marc Zyngier
2021-08-05 15:30             ` Sam Protsenko
2021-08-05 15:50               ` Marc Zyngier
2021-08-04 18:36       ` Krzysztof Kozlowski
2021-08-04 21:30         ` Sam Protsenko
2021-08-05  7:17           ` Krzysztof Kozlowski
2021-08-05  7:30             ` Marc Zyngier
2021-08-05  7:35               ` Krzysztof Kozlowski
2021-07-31  9:03   ` Krzysztof Kozlowski
2021-08-05 23:06     ` Sam Protsenko
2021-08-06  7:48       ` Krzysztof Kozlowski
2021-08-06 12:07         ` Sam Protsenko
2021-08-06 12:32           ` Krzysztof Kozlowski
2021-08-06 12:48             ` Krzysztof Kozlowski
2021-08-06 16:57               ` Sam Protsenko
2021-08-06 20:32             ` Paweł Chmiel
2021-09-06 15:16               ` Sam Protsenko
2021-07-30 15:18 ` [PATCH 00/12] Add minimal support for Exynos850 SoC Krzysztof Kozlowski
2021-07-30 17:21   ` Krzysztof Kozlowski
2021-07-30 19:02     ` Sam Protsenko
2021-07-31  7:29       ` Krzysztof Kozlowski
2021-07-31  8:12         ` Krzysztof Kozlowski
2021-08-02 23:27           ` Sam Protsenko
2021-08-03  7:41             ` Krzysztof Kozlowski

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