linux-kernel - Re: [PATCH] watchdog: rzg2l_wdt: Issue a reset before we put the PM clocks

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Date:   Mon, 14 Nov 2022 20:11:02 +0000
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Biju Das <biju.das.jz@...renesas.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        Fabrizio Castro <fabrizio.castro.jz@...esas.com>,
        Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH] watchdog: rzg2l_wdt: Issue a reset before we put the PM clocks

Hi Geert,

On Mon, Nov 14, 2022 at 7:03 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Biju,
>
> On Mon, Nov 14, 2022 at 7:42 PM Biju Das <biju.das.jz@...renesas.com> wrote:
> > > -----Original Message-----
> > > From: Prabhakar <prabhakar.csengg@...il.com>
> > > Sent: 14 November 2022 18:09
> > > To: Geert Uytterhoeven <geert+renesas@...der.be>; Wim Van Sebroeck
> > > <wim@...ux-watchdog.org>; Guenter Roeck <linux@...ck-us.net>; Philipp Zabel
> > > <p.zabel@...gutronix.de>; linux-watchdog@...r.kernel.org
> > > Cc: linux-kernel@...r.kernel.org; linux-renesas-soc@...r.kernel.org;
> > > Prabhakar <prabhakar.csengg@...il.com>; Biju Das
> > > <biju.das.jz@...renesas.com>; Fabrizio Castro
> > > <fabrizio.castro.jz@...esas.com>; Prabhakar Mahadev Lad <prabhakar.mahadev-
> > > lad.rj@...renesas.com>
> > > Subject: [PATCH] watchdog: rzg2l_wdt: Issue a reset before we put the PM
> > > clocks
> > >
> > > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > >
> > > On RZ/Five SoC it was observed that setting timeout (to say 1 sec) wouldn't
> > > reset the system. To fix this we make sure we issue a reset before putting
> > > the PM clocks to make sure the registers have been cleared.
> > >
> > > While at it re-used rzg2l_wdt_stop() in rzg2l_wdt_set_timeout() as we were
> > > calling the same functions here.
> > >
> > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > ---
> > > Note,
> > > - This patch has been tested on RZ/G2L, RZ/V2M and RZ/Five.
> > > - My initial investigation showed adding the delay after
> > > pm_runtime_get_sync()
> > >   also fixed this issue.
> > > - Do I need add the fixes tag ? what should be the operation PUT-
> > > >RESET/RESET->PUT?
> >
> > It looks like timing issue, None of the previous devices are affected by this.
>
> To me it looks like the device must be clocked for the reset signal
> to be propagated?
>
In the HW manual (7.4.3 Procedure for Activating Modules) it does
state the below before applying the reset signal,

Set up the clock control register for the clock signal connected to
the target module to start the supply of the clock.
Note that the PLL for the clock should be started before the clock if
the PLL is stopped.

So maybe I can add the fixes tag in v2.

Cheers,
Prabhakar