Re: [PATCH v5 00/26] Fix watchdog on Renesas R-Car Gen2 and RZ/G1

From: Simon Horman <horms@verge.net.au>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Michael Turquette <mturquette@baylibre.com>,
	Will Deacon <will.deacon@arm.com>,
	Wolfram Sang <wsa+renesas@sang-engineering.com>,
	Wim Van Sebroeck <wim@iguana.be>,
	linux-clk <linux-clk@vger.kernel.org>,
	Magnus Damm <magnus.damm@gmail.com>,
	Russell King <linux@armlinux.org.uk>,
	Guenter Roeck <linux@roeck-us.net>,
	Fabrizio Castro <fabrizio.castro@bp.renesas.com>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
	<devicetree@vger.kernel.org>,
	Chris Paterson <Chris.Paterson2@renesas.com>,
	Linux Watchdog Mailing List <linux-watchdog@vger.kernel.org>,
	Biju Das <biju.das@bp.renesas.com>,
	Rob Herring <robh+dt@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Stephen Boyd <sboyd@codeaurora.org>,
	Linux-Renesas <linux-renesas-soc@vge>
Subject: Re: [PATCH v5 00/26] Fix watchdog on Renesas R-Car Gen2 and RZ/G1
Date: Tue, 13 Mar 2018 21:05:50 +0100	[thread overview]
Message-ID: <20180313200548.fgexoxlha3coa7hs@verge.net.au> (raw)
In-Reply-To: <CAMuHMdVKPFSVTbnQy9RwAg13OC3R=H1PN9+1FyU0SDHQPa1cuQ@mail.gmail.com>

On Thu, Mar 01, 2018 at 11:20:11AM +0100, Geert Uytterhoeven wrote:
> Hi Simon,
> 
> On Fri, Feb 23, 2018 at 9:14 AM, Simon Horman <horms@verge.net.au> wrote:
> > On Thu, Feb 22, 2018 at 09:38:39AM +0100, Geert Uytterhoeven wrote:
> >> On Wed, Feb 21, 2018 at 7:32 PM, Simon Horman <horms@verge.net.au> wrote:
> >> > On Wed, Feb 21, 2018 at 05:30:12PM +0100, Geert Uytterhoeven wrote:
> >> >> On Wed, Feb 21, 2018 at 5:13 PM, Simon Horman <horms@verge.net.au> wrote:
> >> >> > On Tue, Feb 20, 2018 at 01:51:28PM +0100, Geert Uytterhoeven wrote:
> >> >> >> On Mon, Feb 12, 2018 at 6:44 PM, Fabrizio Castro
> >> >> >> <fabrizio.castro@bp.renesas.com> wrote:
> >> >> >> > this series has been around for some time as RFC, and it has collected
> >> >> >> > useful comments from the community along the way.
> >> >> >> > The solution proposed by this patch set works for most R-Car Gen2 and
> >> >> >> > RZ/G1 devices, but not all of them. We now know that for some R-Car
> >> >> >> > Gen2 early revisions there is no proper software fix. Anyway, no
> >> >> >> > product has been built around early revisions, but development boards
> >> >> >> > mounting early revisions (basically prototypes) are still out there.
> >> >> >> > As a result, this series isn't enabling the internal watchdog on R-Car
> >> >> >> > Gen2 boards, developers may enable it in board specific device trees
> >> >> >> > if needed.
> >> >> >> > This series has been tested by me on the iwg20d, iwg22d, Lager, Alt,
> >> >> >> > and Koelsch boards.
> >> >> >> >
> >> >> >> > The problem
> >> >> >> > ===========
> >> >> >> > To deal with SMP on R-Car Gen2 and RZ/G1, we install a reset vector
> >> >> >> > to ICRAM1 and we program the [S]BAR registers so that when we turn ON
> >> >> >> > the non-boot CPUs they are redirected to the reset vector installed by
> >> >> >> > Linux in ICRAM1, and eventually they continue the execution to RAM,
> >> >> >> > where the SMP bring-up code will take care of the rest.
> >> >> >> > The content of the [S]BAR registers survives a watchdog triggered reset,
> >> >> >> > and as such after the watchdog fires the boot core will try and execute
> >> >> >> > the SMP bring-up code instead of jumping to the bootrom code.
> >> >> >> >
> >> >> >> > The fix
> >> >> >> > =======
> >> >> >> > The main strategy for the solution is to let the reset vector decide
> >> >> >> > if it needs to jump to shmobile_boot_fn or to the bootrom code.
> >> >> >> > In a watchdog triggered reset scenario, since the [S]BAR registers keep
> >> >> >> > their values, the boot CPU will jump into the newly designed reset
> >> >> >> > vector, the assembly routine will eventually test WOVF (a bit in register
> >> >> >> > RWTCSRA that indicates if the watchdog counter has overflown, the value
> >> >> >> > of this bit gets retained in this scenario), and jump to the bootrom code
> >> >> >> > which will in turn load up the bootloader, etc.
> >> >> >> > When bringing up SMP or using CPU hotplug, the reset vector will jump
> >> >> >> > to shmobile_boot_fn instead.
> >> >> >> >
> >> >> >> > Thank you All for your help.
> >> >> >> >
> >> >> >> > Best regards,
> >> >> >> >
> >> >> >> > Fabrizio Castro (26):
> >> >> >> >   ARM: shmobile: Add watchdog support
> >> >> >> >   ARM: dts: r8a7743: Adjust SMP routine size
> >> >> >> >   ARM: dts: r8a7745: Adjust SMP routine size
> >> >> >> >   ARM: dts: r8a7790: Adjust SMP routine size
> >> >> >> >   ARM: dts: r8a7791: Adjust SMP routine size
> >> >> >> >   ARM: dts: r8a7792: Adjust SMP routine size
> >> >> >> >   ARM: dts: r8a7793: Adjust SMP routine size
> >> >> >> >   ARM: dts: r8a7794: Adjust SMP routine size
> >> >> >> >   soc: renesas: rcar-rst: Enable watchdog as reset trigger for Gen2
> >> >> >> >   ARM: shmobile: rcar-gen2: Add watchdog support
> >> >> >> >   dt-bindings: watchdog: renesas-wdt: Add R-Car Gen2 support
> >> >> >> >   watchdog: renesas_wdt: Add R-Car Gen2 support
> >> >> >> >   watchdog: renesas_wdt: Add restart handler
> >> >> >> >   ARM: shmobile: defconfig: Enable RENESAS_WDT_GEN
> >> >> >> >   clk: renesas: r8a7743: Add rwdt clock
> >> >> >> >   clk: renesas: r8a7745: Add rwdt clock
> >> >> >> >   clk: renesas: r8a7790: Add rwdt clock
> >> >> >> >   clk: renesas: r8a7791/r8a7793: Add rwdt clock
> >> >> >> >   clk: renesas: r8a7794: Add rwdt clock
> >> >> >> >   ARM: dts: r8a7743: Add watchdog support to SoC dtsi
> >> >> >> >   ARM: dts: r8a7745: Add watchdog support to SoC dtsi
> >> >> >> >   ARM: dts: r8a7790: Add watchdog support to SoC dtsi
> >> >> >> >   ARM: dts: r8a7791: Add watchdog support to SoC dtsi
> >> >> >> >   ARM: dts: r8a7794: Add watchdog support to SoC dtsi
> >> >> >> >   ARM: dts: iwg20m: Add watchdog support to SoM dtsi
> >> >> >> >   ARM: dts: iwg22m: Add watchdog support to SoM dtsi
> >> >> >> >
> >> >> >> >  .../devicetree/bindings/watchdog/renesas-wdt.txt   | 19 ++++++--
> >> >> >> >  arch/arm/boot/dts/r8a7743-iwg20m.dtsi              |  5 ++
> >> >> >> >  arch/arm/boot/dts/r8a7743.dtsi                     | 12 ++++-
> >> >> >> >  arch/arm/boot/dts/r8a7745-iwg22m.dtsi              |  5 ++
> >> >> >> >  arch/arm/boot/dts/r8a7745.dtsi                     | 12 ++++-
> >> >> >> >  arch/arm/boot/dts/r8a7790.dtsi                     | 12 ++++-
> >> >> >> >  arch/arm/boot/dts/r8a7791.dtsi                     | 12 ++++-
> >> >> >> >  arch/arm/boot/dts/r8a7792.dtsi                     |  2 +-
> >> >> >> >  arch/arm/boot/dts/r8a7793.dtsi                     |  2 +-
> >> >> >> >  arch/arm/boot/dts/r8a7794.dtsi                     | 12 ++++-
> >> >> >> >  arch/arm/configs/shmobile_defconfig                |  1 +
> >> >> >> >  arch/arm/mach-shmobile/common.h                    |  6 +++
> >> >> >> >  arch/arm/mach-shmobile/headsmp.S                   | 55 ++++++++++++++++++++++
> >> >> >> >  arch/arm/mach-shmobile/platsmp-apmu.c              |  1 +
> >> >> >> >  arch/arm/mach-shmobile/pm-rcar-gen2.c              | 15 ++++--
> >> >> >> >  drivers/clk/renesas/r8a7743-cpg-mssr.c             |  2 +
> >> >> >> >  drivers/clk/renesas/r8a7745-cpg-mssr.c             |  2 +
> >> >> >> >  drivers/clk/renesas/r8a7790-cpg-mssr.c             |  2 +
> >> >> >> >  drivers/clk/renesas/r8a7791-cpg-mssr.c             |  2 +
> >> >> >> >  drivers/clk/renesas/r8a7794-cpg-mssr.c             |  2 +
> >> >> >> >  drivers/soc/renesas/rcar-rst.c                     | 35 +++++++++++---
> >> >> >> >  drivers/watchdog/renesas_wdt.c                     | 39 +++++++++++++--
> >> >> >>
> >> >> >> Thanks, I've queued the clock patches in clk-renesas-for-v4.17, as they are
> >> >> >> a hard dependency for:
> >> >> >>   (1) The new reset vector in arch/arm/mach-shmobile/
> >> >> >>   (2) The watchdog driver.
> >> >> >>
> >> >> >> Note that the watchdog driver itself (2) has a hard dependency on the
> >> >> >> new reset vector (1).
> >> >> >
> >> >> > Thanks, I have marked the watchdog driver patch as Deferred.
> >> >> > Please resubmit or otherwise ping me once they dependencies
> >> >> > are in an rc release.
> >> >>
> >> >> I gave the dependencies a bit more thought.
> >> >>
> >> >> I think we can gain once release cycle if you would postpone the DTS patches
> >> >> (both SMP routine size adjustments and RWDT device node additions) to v4.18.
> >> >> Then all other parts can be upstreamed in parallel in v4.17, as nothing
> >> >> will be activated before the DTS parts are in.
> >> >>
> >> >> Does this look sane?
> >> >
> >> > What about new DTS on old kernels of a specific vintage?
> >>
> >> New DTS would work fine on v4.16 and older, which don't have any of the
> >> other patches from this series.
> >> New DTS would work fine on v4.17, assumed all other patches from this
> >> series get into v4.17.
> >>
> >> The only issue would be a new DTS on a kernel that has some but not all
> >> other patches from this series.
> >
> > Thanks for the analysis. I think this is the key point. What is the risk of
> > that happening?
> 
> I think the risk is fairly low.
> You control when the DTS changes go in, and also when they are backported
> to LTSI.
> 
> >> If we want to fast-track everything into v4.17, we need a stable branch, to be
> >> pulled by all 5 actors (clk-renesas, mach-shmobile, soc-renesas, watchdog,
> >> renesas-dts).
> >
> > It seems that watchdog is the only item on that list that neither you nor I
> > sign off on. So I conclude that if the watchdog patch goes in early enough
> > in the cycle then we ought to be in good shape.
> >
> > None the less, is it worth the risk?
> 
> Do we want the functionality early, or can we wait until v4.19?

I understand that the watchdog driver has been accepted and that as things
currently stand if it is enabled in the build it will be enabled in DT and
a crash will result. From my POV that is a regression so I have decided
to adopt the alternate plan proposed by Geert above: in short drop DT
patches (to avoid enabling broken driver) and enqueue mach-shmobile
patches (which don't make things any worse.

Patch-by-patch things are as follows.

Dropped from "[PATCH v5 00/26] Fix watchdog on Renesas R-Car Gen2 and RZ/G1":

979d28f29742 ARM: dts: r8a7743: Adjust SMP routine size
0b205f679f5d ARM: dts: r8a7745: Adjust SMP routine size
2ad21a1d78b3 ARM: dts: r8a7790: Adjust SMP routine size
82c978459c77 ARM: dts: r8a7791: Adjust SMP routine size
d303698e6ff3 ARM: dts: r8a7792: Adjust SMP routine size
d8b8b9a1e295 ARM: dts: r8a7793: Adjust SMP routine size
70b3ab369773 ARM: dts: r8a7794: Adjust SMP routine size

ebf26cf1b1de ARM: dts: r8a7743: Add watchdog support to SoC dtsi
5a4566ab3777 ARM: dts: r8a7745: Add watchdog support to SoC dtsi
acd58e2bb1e5 ARM: dts: r8a7790: Add watchdog support to SoC dtsi
e3f89168e72f ARM: dts: r8a7791: Add watchdog support to SoC dtsi
e76a6a69a1fc ARM: dts: r8a7794: Add watchdog support to SoC dtsi
242cc1ab7f7c ARM: dts: iwg20m: Add watchdog support to SoM dtsi
748ed07f6c7c ARM: dts: iwg22m: Add watchdog support to SoM dtsi

Dropped from "[PATCH/RFC 00/11] ARM: dts: rcar-gen2: Enable watchdog support":

c257202482e2 ARM: dts: r8a7792: Add RWDT node
01ec04dec8eb ARM: dts: r8a7793: Add RWDT node
8e6ebe4f2f94 ARM: dts: lager: Enable watchdog support
f223ad0198f6 ARM: dts: koelsch: Enable watchdog support
1d14d2bb700d ARM: dts: porter: Enable watchdog support
bf71652fc955 ARM: dts: blanche: Enable watchdog support
13a0b10aeea4 ARM: dts: wheat: Enable watchdog support
4e247bf110b8 ARM: dts: gose: Enable watchdog support
2dcbd24bbf5e ARM: dts: alt: Enable watchdog support
7f6844c900b4 ARM: dts: silk: Enable watchdog support

And applied:

[v5] ARM: shmobile: rcar-gen2: Add watchdog support
[v5] ARM: shmobile: Add watchdog support

In the case of the last patch above I removed the #ifdef from the header file.