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

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Message-ID: <50D073BC.3040607@gmail.com>
Date:	Tue, 18 Dec 2012 07:46:36 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Hiroshi Doyu <hdoyu@...dia.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

On 12/18/2012 03:21 AM, Hiroshi Doyu wrote:
> 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?

The A15/A7 still have the register for the other peripherals like the
GIC, but there are no SCU registers or other way to get a core count
from the h/w.

The DT node could be used to determine if you have an SCU or not. I just
used the cpu node compatible value to determine that.

>> 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.

Well, reading the cp15 register and mapping the registers could be
common code independent of DT. I'm not sure if there are non-A9
implementations of the SCU which don't have the cp15 register.

Rob
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