[RFC v3 11/25] watchdog: renesas_wdt: Add R-Car Gen2 support

[Fabrizio Castro]

Hi Geert,

thank you for your feedback!

> Subject: Re: [RFC v3 11/25] watchdog: renesas_wdt: Add R-Car Gen2 support
>
> Hi Fabrizio,
>
> On Wed, Jan 31, 2018 at 11:47 AM, Fabrizio Castro
> <fabrizio.castro at bp.renesas.com> wrote:
> >> Subject: Re: [RFC v3 11/25] watchdog: renesas_wdt: Add R-Car Gen2 support
> >> On Tue, Jan 30, 2018 at 08:22:44PM +0000, Fabrizio Castro wrote:
> >> > On R-Car Gen2 and RZ/G1 the rwdt clock needs to be always ON, therefore
> >> > when suspending to RAM we need to explicitly disable the counting by
> >> > clearing TME from RWTCSRA.
> >> > Also, on some systems RWDT is the only piece of HW that allows the SoC
> >> > to be restarted, therefore this patch implements the restart callback.
> >> >
> >> > Signed-off-by: Fabrizio Castro <fabrizio.castro at bp.renesas.com>
> >> > Signed-off-by: Ramesh Shanmugasundaram <ramesh.shanmugasundaram at bp.renesas.com>
> >> > ---
> >> > Wolfram, was the restart callback implementation missing for a reason?
> >> > Is its implementation going to break any Gen3 platform?
> >>
> >> The changes clearly are way more than claimed in the subject. Adding
> >> restart handler and PM support may be prerequisites for Gen2, but the
> >> changes apply to Gen3 as well. What happened to "one patch per logical
> >> change" ?
> >
> > The PM implementation should be ok for Gen3 too, without this patch series the kernel
> > would disable the rwdt clock when suspending to RAM, this would "pause" the counting.
> > This patch series declares the rwdt clock as critical for Gen2 and RZ/G1, which means we
> > need to explicitly disable the counting to keep the same behaviour in place.
>
> Note that if the kernel crashes after rwdt_suspend(), the watchdog won't
> restart the system. But that's an issue common to many watchdog driver, right?

yeah, there isn't much we can do about this. Even without rwdt_suspend in place, if the
kernel crashes after disabling the rwdt clock the watchdog won't restart the system.

>
> > With respect to the restart callback implementation, that may well have consequences on
> > Gen3, hopefully Wolfram will give us a feedback on this.
> > In particular I would like to know if we should be installing the restart callback only when
> > we use "renesas,rcar-gen2-wdt" as compatible string, or it's ok to make it available for
> > Gen3 as well.
>
> IIRC, the reason we don't have the restart callback on R-Car Gen3 is the
> arm64 maintainers insisting on using PSCI, and vetoing other means,
> to restart the system.
>
> Which leaves us with a few boards where we have to use the watchdog, and
> wait until the timeout triggers...

ok, for the next version I'll register the restart callback only when we match
"renesas,rcar-gen2-wdt". Since currently there is no watchdog support on Gen2
I believe such a change is perfectly safe.

>
> > The only way to reboot iWave's boards iwg20d and iwg22d is to use the internal watchdog,
> > that's why the restart implementation was merged into this patch.
> > I can split this patch in two, one for PM support and one for restart support for the next
> > version, what do you think about this?
>
> Splitting in individual logical changes sounds like a good idea to me.

agreed then, I'll split the commit in two for the next version.

Thanks,
Fab

>
> 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



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