linux-kernel - Re: [PATCH 2/2] watchdog: rzg2l_wdt: Handle TYPE-B reset for RZ/V2M

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Message-ID: <CAMuHMdXxri6GgGxJy9WC-ktM_zoXDkzRz-6yBqQcikVe3DPShg@mail.gmail.com>
Date:   Mon, 16 Jan 2023 17:22:18 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Fabrizio Castro <fabrizio.castro.jz@...esas.com>
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Biju Das <biju.das.jz@...renesas.com>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Biju Das <biju.das@...renesas.com>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Jacopo Mondi <jacopo@...ndi.org>
Subject: Re: [PATCH 2/2] watchdog: rzg2l_wdt: Handle TYPE-B reset for RZ/V2M

Hi Fabrizio,

On Mon, Jan 16, 2023 at 5:18 PM Fabrizio Castro
<fabrizio.castro.jz@...esas.com> wrote:
> > On Thu, Nov 17, 2022 at 12:49 PM Fabrizio Castro
> > <fabrizio.castro.jz@...esas.com> wrote:
> > > As per section 48.4 of the HW User Manual, IPs in the RZ/V2M
> > > SoC need either a TYPE-A reset sequence or a TYPE-B reset
> > > sequence. More specifically, the watchdog IP needs a TYPE-B
> > > reset sequence.
> > >
> > > If the proper reset sequence isn't implemented, then resetting
> > > IPs may lead to undesired behaviour. In the restart callback of
> > > the watchdog driver the reset has basically no effect on the
> > > desired funcionality, as the register writes following the reset
> > > happen before the IP manages to come out of reset.
> > >
> > > Implement the TYPE-B reset sequence in the watchdog driver to
> > > address the issues with the restart callback on RZ/V2M.
> > >
> > > Fixes: ec122fd94eeb ("watchdog: rzg2l_wdt: Add rzv2m support")
> > > Signed-off-by: Fabrizio Castro <fabrizio.castro.jz@...esas.com>
> >
> > Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
> >
> > Perhaps this logic can be incorporated into the RZ/V2M reset controller
> > driver later, so reset consumers don't have to care about TYPE-A and
> > TYPE-B reset, but can just call reset_control_reset()?
> > I understand that's not gonna be easy, as it needs to know about the
> > relation between resets and clocks, and how to handle both cases (clock
> > (not) switched off) for TYPE-B resets.
>
> Yeah, we have been thinking about dealing with this in the reset controller
> driver, but as you pointed out it's not going to be simple, and therefore
> it'll take some time. This change will guarantee the correct behaviour of
> the watchdog for now, we'll tackle the larger issue later on, if that's okay
> with you.

Fine for me.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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