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From:   Jonas Danielsson <jonas@orbital-systems.com>
Date:   Tue, 16 Oct 2018 16:15:37 +0200
Message-ID: <CALDOjzgxftbv=ePKcgXyDYZefve0Codqs5K-biDcgQRtpTRFYQ@mail.gmail.com>
Subject: Re: [PATCH] power: reset: at91-reset: enable I-cache for at91sam9260_reset
To:     Claudiu.Beznea@microchip.com
Cc:     linux-kernel@vger.kernel.org, Sebastian Reichel <sre@kernel.org>,
        Nicolas Ferre <Nicolas.Ferre@microchip.com>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org
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On Tue, Oct 16, 2018 at 3:30 PM <Claudiu.Beznea@microchip.com> wrote:
>
> Hi Jonas,
>

Hi,

> On 07.10.2018 15:57, Jonas Danielsson wrote:
> > From: Jonas Danielsson <jonas@orbital-systems.com>
> >
> > This fixes a bug where our embedded system (AT91SAM9260 based) would
> > hang at reboot. At the most we managed 16 boot loops without a hang.
> >
> > With this patch applied the problem has not been observed and the board
> > has managed above 250 boot loops.
> >
> > The AT91SAM9260 datasheet tells us that with the instruction cache
> > disabled all instructions are fetched from SDRAM. And we have an errata
> > telling us we must power down the SDRAM before issuing cpu reset.
> >
> > This means we need the instruction cache enabled in at91sam9260_reset()
> > At the moment it is being disabled in cpu_proc_fin() which is called fr=
om
> > arch/arm/kernel/reboot.c.
>
> Are you using kexec reboot or implemented hibernate mode on this machine?
> I'm seeing cpu_proc_fin() is called only in case of kexec reboot or
> switching to hibernate mode.
>
> In case of normal reboot (e.g. reboot command) machine_restart() from
> arch/arm/kernel/reboot.c is called. Please correct me if I'm wrong.
>

We are not, we do regular reboots. I have read the code paths wrong.
Then I wonder what disables icache.

> Thank you,
> Claudiu Beznea

Thank you!

>
> >
> > Signed-off-by: Jonas Danielsson <jonas@orbital-systems.com>
> > ---
> >  drivers/power/reset/at91-reset.c | 12 +++++++++++-
> >  1 file changed, 11 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/power/reset/at91-reset.c b/drivers/power/reset/at9=
1-reset.c
> > index f44a9ffcc2ab..78972bba64df 100644
> > --- a/drivers/power/reset/at91-reset.c
> > +++ b/drivers/power/reset/at91-reset.c
> > @@ -50,14 +50,24 @@ static void __iomem *at91_ramc_base[2], *at91_rstc_=
base;
> >  static struct clk *sclk;
> >
> >  /*
> > -* unless the SDRAM is cleanly shutdown before we hit the
> > +* Errata 43.1.7.1 RSTC: Reset during SDRAM Accesses
> > +*
> > +* Unless the SDRAM is cleanly shutdown before we hit the
> >  * reset register it can be left driving the data bus and
> >  * killing the chance of a subsequent boot from NAND
> > +*
> > +* Since we are disabling SDRAM need to make sure that the
> > +* instruction cache is enabled.
> >  */
> >  static int at91sam9260_restart(struct notifier_block *this, unsigned l=
ong mode,
> >                              void *cmd)
> >  {
> >       asm volatile(
> > +             /* Enable I-cache */
> > +             "mrc    p15, 0, r0, c1, c0, 0\n\t"
> > +             "orr    r0, r0, #4096\n\t" /* CR_I (bit 12) */
> > +             "mcr    p15, 0, r0, c1, c0, 0\n\t"
> > +
> >               /* Align to cache lines */
> >               ".balign 32\n\t"
> >
> >


--=20


JONAS DANIELSSON
Software Developer

+46 72 361 5022
Malm=C3=B6 - Sweden

ORBITAL SYSTEMS
orbital-systems.com


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