[PATCH V2 1/5] arm: mvebu: Added support for coherency fabric in mach-mvebu

[gregory.clement@free-electrons.com (Gregory CLEMENT)]

On 11/13/2012 11:43 AM, Will Deacon wrote:
> On Mon, Nov 12, 2012 at 08:21:07PM +0000, Gregory CLEMENT wrote:
>> On 11/05/2012 03:02 PM, Will Deacon wrote:
>>> On Mon, Oct 29, 2012 at 09:11:44PM +0000, Gregory CLEMENT wrote:
>>>> +int set_cpu_coherent(unsigned int hw_cpu_id, int smp_group_id)
>>>> +{
>>>> +	int reg;
>>>> +
>>>> +	if (!coherency_base) {
>>>> +		pr_warn("Can't make CPU %d cache coherent.\n", hw_cpu_id);
>>>> +		pr_warn("Coherency fabric is not initialized\n");
>>>> +		return 1;
>>>> +	}
>>>> +
>>>> +	/* Enable the CPU in coherency fabric */
>>>> +	reg = readl(coherency_base + COHERENCY_FABRIC_CTL_OFFSET);
>>>> +	reg |= 1 << (24 + hw_cpu_id);
>>>> +	writel(reg, coherency_base + COHERENCY_FABRIC_CTL_OFFSET);
>>>> +
>>>> +	/* Add CPU to SMP group */
>>>> +	reg = readl(coherency_base + COHERENCY_FABRIC_CFG_OFFSET);
>>>> +	reg |= 1 << (16 + hw_cpu_id + (smp_group_id == 0 ? 8 : 0));
>>>> +	writel(reg, coherency_base + COHERENCY_FABRIC_CFG_OFFSET);
>>>> +
>>>> +	return 0;
>>>> +}
>>>
>>> These writels may expand to code containing calls to outer_sync(), which
>>> will attempt to take a spinlock for the aurora l2. Given that the CPU isn't
>>> coherent, how does this play out with the exclusive store instruction in the
>>> lock?
>>
>> I dug a little this subject: and I am not sure there is problem. In SMP mode,
>> only the system cache mode of Aurora is used. In this mode, outer_cache.sync
>> is void then outer_sync() won't call any function, so there will be no
>> access to any spinlock.
> 
> Hmm, that is pretty subtle and it doesn't really solve the bigger picture.
> printk takes logbuf_lock, for example, and I'm sure that by the time you get
> to this code you will have relied on exclusives behaving correctly.
> 

Hi Will,
I get an answer from Marvell engineers:
"STREX on non-shareable and/or non-cacheable memory regions is supported."

Gregory