linux-kernel - Re: [PATCH v4 10/10] ARM: sunxi: smp: Add initialization of CNTVOFF

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Message-ID: <20180226101252.ozdsxjvawgkemz2c@flea.lan>
Date:   Mon, 26 Feb 2018 11:12:52 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Mylène Josserand <mylene.josserand@...tlin.com>,
        Russell King <linux@...linux.org.uk>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        LABBE Corentin <clabbe.montjoie@...il.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        quentin.schulz@...tlin.com
Subject: Re: [PATCH v4 10/10] ARM: sunxi: smp: Add initialization of CNTVOFF

On Sat, Feb 24, 2018 at 12:17:13AM +0800, Chen-Yu Tsai wrote:
> On Fri, Feb 23, 2018 at 9:37 PM, Mylène Josserand
> <mylene.josserand@...tlin.com> wrote:
> > On Cortex-A7, the CNTVOFF register from arch timer is uninitialized.
> > It should be done by the bootloader but it is currently not the case,
> > even for boot CPU because this SoC is booting in secure mode.
> > It leads to an random offset value meaning that each CPU will have a
> > different time, which isn't working very well.
> >
> > Add assembly code used for boot CPU and secondary CPU cores to make
> > sure that the CNTVOFF register is initialized.
> >
> > Signed-off-by: Mylène Josserand <mylene.josserand@...tlin.com>
> > ---
> >  arch/arm/mach-sunxi/headsmp.S | 21 +++++++++++++++++++++
> >  arch/arm/mach-sunxi/sunxi.c   |  4 ++++
> >  2 files changed, 25 insertions(+)
> >
> > diff --git a/arch/arm/mach-sunxi/headsmp.S b/arch/arm/mach-sunxi/headsmp.S
> > index d5c97e945e69..605896251927 100644
> > --- a/arch/arm/mach-sunxi/headsmp.S
> > +++ b/arch/arm/mach-sunxi/headsmp.S
> > @@ -65,9 +65,30 @@ ENTRY(sunxi_mc_smp_cluster_cache_enable)
> >         first: .word sunxi_mc_smp_first_comer - .
> >  ENDPROC(sunxi_mc_smp_cluster_cache_enable)
> >
> > +ENTRY(sunxi_init_cntvoff)
> > +       /*
> > +        * CNTVOFF has to be initialized either from non-secure Hypervisor
> > +        * mode or secure Monitor mode with SCR.NS==1. If TrustZone is enabled
> > +        * then it should be handled by the secure code
> > +        */
> > +       cps     #MON_MODE
> > +       mrc     p15, 0, r1, c1, c1, 0           /* Get Secure Config */
> > +       orr     r0, r1, #1
> > +       mcr     p15, 0, r0, c1, c1, 0           /* Set Non Secure bit */
> > +       instr_sync
> > +       mov     r0, #0
> > +       mcrr    p15, 4, r0, r0, c14             /* CNTVOFF = 0 */
> > +       instr_sync
> > +       mcr     p15, 0, r1, c1, c1, 0           /* Set Secure bit */
> > +       instr_sync
> > +       cps     #SVC_MODE
> > +       ret     lr
> > +ENDPROC(sunxi_init_cntvoff)
> 
> There is no need to move all the assembly into a separate file, just
> to add this function. Everything can be inlined as a naked function.
> The "instr_sync" macro can be replaced with "isb", which is what it
> expands to anyway.
> 
> I really want to keep everything self-contained without global symbols,
> and in C files if possible.

What is the rationale for keeping it in C files (beside the global
symbols)? Because the syntax is quite ugly, and it's much easier to
read, review and amend using a separate file.

> >  #ifdef CONFIG_SMP
> >  ENTRY(sunxi_boot)
> >         bl      sunxi_mc_smp_cluster_cache_enable
> > +       bl      sunxi_init_cntvoff
> >         b       secondary_startup
> >  ENDPROC(sunxi_boot)
> >
> > diff --git a/arch/arm/mach-sunxi/sunxi.c b/arch/arm/mach-sunxi/sunxi.c
> > index 5e9602ce1573..4bb041492b54 100644
> > --- a/arch/arm/mach-sunxi/sunxi.c
> > +++ b/arch/arm/mach-sunxi/sunxi.c
> > @@ -37,8 +37,12 @@ static const char * const sun6i_board_dt_compat[] = {
> >  };
> >
> >  extern void __init sun6i_reset_init(void);
> > +extern void sunxi_init_cntvoff(void);
> > +
> >  static void __init sun6i_timer_init(void)
> >  {
> > +       sunxi_init_cntvoff();
> 
> You should check the enable-method to see if PSCI is set or not,
> as an indicator whether the kernel is booted secure or non-secure.

It's an indicator, but it's not really a perfect one. You could very
well have your kernel booted in non-secure, without PSCI. Or even with
PSCI, but without the SMP ops.

We have a quite big number of these cases already, where, depending on
the configuration, we might not have access to the device we write to,
the number of hacks to just enable that device for non-secure is a
good example of that.

> AFAIK trying to set CNTVOFF under non-secure would be very bad.

Just like any other access we do :/

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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