linux-kernel - Re: [PATCH 4/4] ARM: tegra: Set SCU base address dynamically from DT

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Message-ID: <20121218.112129.1344593225772728837.hdoyu@nvidia.com>
Date:	Tue, 18 Dec 2012 10:21:29 +0100
From:	Hiroshi Doyu <hdoyu@...dia.com>
To:	"robherring2@...il.com" <robherring2@...il.com>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	"rob@...dley.net" <rob@...dley.net>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 4/4] ARM: tegra: Set SCU base address dynamically from DT

Hi Rob,

Rob Herring <robherring2@...il.com> wrote @ Mon, 17 Dec 2012 15:00:46 +0100:

> On 12/17/2012 12:18 AM, Hiroshi Doyu wrote:
> > Set Snoop Control Unit(SCU) register base address dynamically from DT.
> > 
> > Signed-off-by: Hiroshi Doyu <hdoyu@...dia.com>
> > ---
> >  arch/arm/mach-tegra/platsmp.c |   23 ++++++++++++++++++++---
> >  1 file changed, 20 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/arm/mach-tegra/platsmp.c b/arch/arm/mach-tegra/platsmp.c
> > index 1b926df..45c0b79 100644
> > --- a/arch/arm/mach-tegra/platsmp.c
> > +++ b/arch/arm/mach-tegra/platsmp.c
> > @@ -18,6 +18,8 @@
> >  #include <linux/jiffies.h>
> >  #include <linux/smp.h>
> >  #include <linux/io.h>
> > +#include <linux/of.h>
> > +#include <linux/of_address.h>
> >  
> >  #include <asm/cacheflush.h>
> >  #include <asm/hardware/gic.h>
> > @@ -36,7 +38,7 @@
> >  
> >  extern void tegra_secondary_startup(void);
> >  
> > -static void __iomem *scu_base = IO_ADDRESS(TEGRA_ARM_PERIF_BASE);
> > +static void __iomem *scu_base;
> >  
> >  #define EVP_CPU_RESET_VECTOR \
> >  	(IO_ADDRESS(TEGRA_EXCEPTION_VECTORS_BASE) + 0x100)
> > @@ -143,14 +145,28 @@ done:
> >  	return status;
> >  }
> >  
> > +static const struct of_device_id cortex_a9_scu_match[] __initconst = {
> > +	{ .compatible = "arm,cortex-a9-scu", },
> > +	{}
> > +};
> > +
> >  /*
> >   * Initialise the CPU possible map early - this describes the CPUs
> >   * which may be present or become present in the system.
> >   */
> >  static void __init tegra_smp_init_cpus(void)
> >  {
> > -	unsigned int i, ncores = scu_get_core_count(scu_base);
> > +	struct device_node *np;
> > +	unsigned int i, ncores = 1;
> > +
> > +	np = of_find_matching_node(NULL, cortex_a9_scu_match);
> > +	if (!np)
> > +		return;
> > +	scu_base = of_iomap(np, 0);
> 
> Did you actually test this? Unless something changed, ioremap does not
> work this early. The only reason to have it mapped this early is to get
> the core count, but that doesn't work on A15 or A7. So we really need to
> get core count/mask in a standard way. At least some work to get core
> count from DT went into 3.8.
> 
> BTW, you can get the scu address on the A9 by reading cp15 register:
> 
> 	/* Get SCU base */
> 	asm("mrc p15, 4, %0, c15, c0, 0" : "=r" (base));
> 
> It's still probably good to have the DT node, but the reg property can
> be optional in this case.

I'm simply wondering, if the above cp15 works with Cortex-A9, do we
still need SCU DT node? At least from Cortex-A15 TRM, it seems that
SCU is tighly integrated into CPU core and it doesn't have any user
control. So Cortex-A15 doesn't seem to need to configure SCU. For
Cortex-A7, I haven't yet found S/W configurable register definitions
in TRM. So if neither of A15/A7 need SCU base, would the above cp15
intructions be enough?

> We need to move away from having the DT matching code within the
> platforms. This should all be moved to the scu code in a scu_of_init
> function that could be called from common code.

True if SCU DT node is still necessary.
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