Re: [PATCH] ARM: EXYNOS: Restore the entry address setup code post-resume

[Nicolas Pitre <nicolas.pitre@linaro.org>]

On Thu, 26 Jun 2014, Abhilash Kesavan wrote:

> Hi,
> 
> On Thu, Jun 26, 2014 at 4:28 PM, Abhilash Kesavan <a.kesavan@samsung.com> wrote:
> > Setup the mcpm entry address again on system resume as the
> > iRAM contents are lost across an s2r cycle.
> >
> > Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
> > ---
> > This has been tested after applying the Exynos5420 S2R support series
> > along with Nicolas Pitre's boot cluster CCI enablement patches on Peach
> > Pit.
> >
> >  arch/arm/mach-exynos/mcpm-exynos.c | 31 +++++++++++++++++++++----------
> >  1 file changed, 21 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/arm/mach-exynos/mcpm-exynos.c b/arch/arm/mach-exynos/mcpm-exynos.c
> > index 8c610e2..0bf734d 100644
> > --- a/arch/arm/mach-exynos/mcpm-exynos.c
> > +++ b/arch/arm/mach-exynos/mcpm-exynos.c
> > @@ -15,6 +15,7 @@
> >  #include <linux/delay.h>
> >  #include <linux/io.h>
> >  #include <linux/of_address.h>
> > +#include <linux/syscore_ops.h>
> >
> >  #include <asm/cputype.h>
> >  #include <asm/cp15.h>
> > @@ -26,6 +27,7 @@
> >  #define EXYNOS5420_CPUS_PER_CLUSTER    4
> >  #define EXYNOS5420_NR_CLUSTERS         2
> >
> > +static void __iomem *ns_sram_base_addr;
> >  /*
> >   * The common v7_exit_coherency_flush API could not be used because of the
> >   * Erratum 799270 workaround. This macro is the same as the common one (in
> > @@ -308,10 +310,26 @@ static const struct of_device_id exynos_dt_mcpm_match[] = {
> >         {},
> >  };
> >
> > +static void exynos_mcpm_setup_entry_point(void)
> > +{
> > +       /*
> > +        * U-Boot SPL is hardcoded to jump to the start of ns_sram_base_addr
> > +        * as part of secondary_cpu_start().  Let's redirect it to the
> > +        * mcpm_entry_point(). This is done during both secondary boot-up as
> > +        * well as system resume.
> > +        */
> > +       __raw_writel(0xe59f0000, ns_sram_base_addr);     /* ldr r0, [pc, #0] */
> > +       __raw_writel(0xe12fff10, ns_sram_base_addr + 4); /* bx  r0 */
> > +       __raw_writel(virt_to_phys(mcpm_entry_point), ns_sram_base_addr + 8);
> > +}
> > +
> > +static struct syscore_ops exynos_mcpm_syscore_ops = {
> > +       .resume = exynos_mcpm_setup_entry_point,
> > +};
> > +
> >  static int __init exynos_mcpm_init(void)
> >  {
> >         struct device_node *node;
> > -       void __iomem *ns_sram_base_addr;
> >         int ret;
> >
> >         node = of_find_matching_node(NULL, exynos_dt_mcpm_match);
> > @@ -357,16 +375,9 @@ static int __init exynos_mcpm_init(void)
> >
> >         pr_info("Exynos MCPM support installed\n");
> >
> > -       /*
> > -        * U-Boot SPL is hardcoded to jump to the start of ns_sram_base_addr
> > -        * as part of secondary_cpu_start().  Let's redirect it to the
> > -        * mcpm_entry_point().
> > -        */
> > -       __raw_writel(0xe59f0000, ns_sram_base_addr);     /* ldr r0, [pc, #0] */
> > -       __raw_writel(0xe12fff10, ns_sram_base_addr + 4); /* bx  r0 */
> > -       __raw_writel(virt_to_phys(mcpm_entry_point), ns_sram_base_addr + 8);
> > +       exynos_mcpm_setup_entry_point();
> >
> > -       iounmap(ns_sram_base_addr);
> > +       register_syscore_ops(&exynos_mcpm_syscore_ops);
> >
> >         return ret;
> >  }
> 
> This patch alone is not enough to bring the 8 cores back up post
> resume on exynos5420, We need to enable the boot cluster snoops as
> well.
> 
> Nicolas, if I add code to enable the boot cluster CCI in
> mach-exynos/sleep.S, all 8 cores come up. However, if I use
> mcpm_loopback as part of the newly added resume function to do the
> same, I get a hang on resume.
> Is there anything else that I need to take care of while doing this ?

No no no.

Forget about the MCPM loopback -- that's for boot time setup of the 
booting cluster nothing else.

The snoops are enabled in a ***race free way*** by the low-level MCPM 
code.  But of course you must call it upon resume.  Nothing else than 
MCPM should ever play with the snoops enable/disable.  Certainly not 
mach-exynos/sleep.S.

You must tell your firmware to resume execution after suspend at 
mcpm_entry_point.  Before suspending, you tell MCPM where it should 
branch to after it is done with its resuming business by calling 
mcpm_set_entry_vector(), passing the address for exynos_cpu_resume for 
example.

And of course the CPU shutdown during idle has to go through MCPM too.

When resumed, you also have to call mcpm_cpu_powered_up().

See how it is done in cpuidle-big_little.c for example.


Nicolas