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

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Message-ID: <dd55eee9-8ddc-f186-0bef-0a15764ff368@arm.com>
Date:   Wed, 7 Mar 2018 12:09:27 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Chen-Yu Tsai <wens@...e.org>,
        Mylène Josserand <mylene.josserand@...tlin.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        devicetree <devicetree@...r.kernel.org>,
        quentin.schulz@...tlin.com,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        LABBE Corentin <clabbe.montjoie@...il.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 10/10] ARM: sunxi: smp: Add initialization of CNTVOFF

On 23/02/18 16:17, 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.
> 
>> +
>>  #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.
> AFAIK trying to set CNTVOFF under non-secure would be very bad.

Absolutely not. CNTVOFF *is* a non-secure register. The fact that it is
not accessible from NS-PL1 is another problem. Please don't conflate the
two things together.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...