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

[geert@linux-m68k.org (Geert Uytterhoeven)]

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?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds