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

[Chen-Yu Tsai <wens@csie.org>]

On Mon, Feb 26, 2018 at 6:12 PM, Maxime Ripard
<maxime.ripard@bootlin.com> wrote:
> 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@bootlin.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@bootlin.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.

Global symbols and keeping everything in one place I guess.
This symbol would be used in a few places, so I suppose having it
in a separate assembly file would be OK.

>> >  #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.

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.

ChenYu

>> 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