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

[MylÃne Josserand]

Hello Mark,

Please, excuse me for this late answer and thank you for the review!

On Wed, 7 Mar 2018 12:18:33 +0000
Marc Zyngier <marc.zyngier@xxxxxxx> wrote:

> On 23/02/18 13:37, MylÃne Josserand wrote:
> > On Cortex-A7, the CNTVOFF register from arch timer is uninitialized.  
> 
> Only on A7? Is that specific to your platform?

I do not really know other Allwinner's platforms about this subject. At
least, the sun9i-a80 which is a Cortex-a15/a7 does not need that but it
is necessary for sun8i-a83t which is a cortex-a7. Maybe, Chen-Yu or
Maxime could help us on it.

> 
> > 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: MylÃne Josserand <mylene.josserand@xxxxxxxxxxx>
> > ---
> >  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  
> 
> Since these CPUs are all ARMv7, you can use isb directly. Nobody wants
> to see more of the CP15 barriers.

Okay, thanks, I will update that.

> 
> > +	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  
> 
> Given that this code is identical to the shmobile hack, it'd be good to
> make it common, one way or another.

Sure, I will try that.
May you have some hints to give me on how to implement it?

> 
> > +ENDPROC(sunxi_init_cntvoff)
> > +
> >  #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();
> > +  
> 
> It is slightly odd that some CPUs get initialized from the early asm
> code, and some others do a detour via some C code. I'm sure this could
> be made to work

Renesa's code was also doing that so I thought it could be ok to do
it.

Without this code in this timer_init function, it fails to initialize
cntvoff correctly:
http://code.bulix.org/i9fhc9-302612?raw

How should I implement that?

> 
> >  	of_clk_init(NULL);
> >  	if (IS_ENABLED(CONFIG_RESET_CONTROLLER))
> >  		sun6i_reset_init();
> >   
> 
> Thanks,
> 
> 	M.

Thanks,

Best regards,

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