From mboxrd@z Thu Jan  1 00:00:00 1970
From: gregory.clement@free-electrons.com (Gregory CLEMENT)
Date: Thu, 26 Jun 2014 17:09:24 +0200
Subject: [PATCH] ARM: mvebu: Enable SCU Speculative linefills to L2 for
 Armada 375/38x
In-Reply-To: <20140626165230.374f285e@free-electrons.com>
References: <1403790178-23902-1-git-send-email-gregory.clement@free-electrons.com>
 <20140626165230.374f285e@free-electrons.com>
Message-ID: <53AC37A4.8090306@free-electrons.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Hi Thomas,

On 26/06/2014 16:52, Thomas Petazzoni wrote:
> Dear Gregory CLEMENT,
> 
> On Thu, 26 Jun 2014 15:42:58 +0200, Gregory CLEMENT wrote:
> 
>> +#define SCU_CTRL		0x00
>> +#define SCU_SPEC_LINEFILL_EN	    BIT(3)
>> +
>> +
>>  /*
>>   * Enables the SCU when available. Obviously, this is only useful on
>>   * Cortex-A based SOCs, not on PJ4B based ones.
>> @@ -44,7 +48,15 @@ static void __init mvebu_scu_enable(void)
>>  	struct device_node *np =
>>  		of_find_compatible_node(NULL, NULL, "arm,cortex-a9-scu");
>>  	if (np) {
>> +		u32 scu_ctrl;
>>  		scu_base = of_iomap(np, 0);
>> +		/* already enabled? */
>> +		scu_ctrl = __raw_readl(scu_base + SCU_CTRL);
> 
> Unless the SCU uses the native endianess of the system, and therefore
> switches to big endian when the system is running big endian, using
> __raw_{readl,writel} is wrong here, and will break big endian
> configurations.

Yes you are right here.

> 
>> +		if (!(scu_ctrl & 1)) {
> 
> What is this bit 0 you're checking here? How does it relate to the bit
> 3 you're setting when bit 0 is not set?

It is related to the comment just before: we checked if the SCU
is already enabled. So I guess we can't set the SCU Speculative linefills
bit if the SCU is enabled.

> 
> A broader question is: if this feature is generic to all Cortex-A9, why
> not offer a function in smp_scu.c to enable it? It seems weird to have
> the offset and bit definitions for something as generic as the SCU
> present deep into a Marvell-specific file.

I have no strong opinion on it, and I also thoough about adding a function
in smp_scu.c but when you are looking at the usage of SCU is the kernel
the other SOC manipulate it directly.


Thanks,

Gregory



-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com