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

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Date:   Mon, 5 Mar 2018 14:51:10 +0100
From:   Mylène Josserand <mylene.josserand@...tlin.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Chen-Yu Tsai <wens@...e.org>, 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

Hello,

On Mon, 5 Mar 2018 09:31:14 +0100
Maxime Ripard <maxime.ripard@...tlin.com> wrote:

> On Mon, Mar 05, 2018 at 08:51:48AM +0100, Mylène Josserand wrote:
> > > >> > 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.    
> > > 
> > > I wouldn't consider them hacks though. The hardware gives the option
> > > to have control of many devices delegated solely to secure-only, or
> > > secure/non-secure. Our present model is to support everything we can
> > > in Linux directly, instead of through some firmware interface to a
> > > non-existent firmware.  
> > 
> > I am not sure to understand what is the conclusion about it.
> > Should I use "psci"/enable-method or should I use another mechanism to
> > detect we are in secure/non-secure (if it exists)?
> > 
> > Otherwise, for the moment, I can use machine-compatible on sun8i-a83t
> > and we will see later how we can handle it in a better way.  
> 
> Can't we have another approach here?
> 
> If we use an enable-method (and we should), instead of having it tied
> to the machine compatible, the SMP setup code will run only if our
> enable-method is the one we set up. If PSCI is in use, the
> enable-method is not going to be the one defined here, and the code
> will not run.
> 
> So why not just move that call to the SMP ops setup function, just
> like renesas does?
> 
> Maxime
> 

Okay, I will update my series and handle the differences using
enable-method instead of machine-compatible.

Best regards,

-- 
Mylène Josserand, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
http://bootlin.com