linux-kernel - Re: [PATCH] powerpc/powernv: Initialise nest mmu

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Message-ID: <a405f24b-2a80-4828-cf65-a40824130f5e@gmail.com>
Date:	Tue, 16 Aug 2016 14:22:33 +1000
From:	Balbir Singh <bsingharora@...il.com>
To:	Alistair Popple <alistair@...ple.id.au>
Cc:	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	benh@...nel.crashing.org, stewart@...ux.vnet.ibm.com,
	mpe@...erman.id.au
Subject: Re: [PATCH] powerpc/powernv: Initialise nest mmu



On 16/08/16 10:37, Alistair Popple wrote:
> Balbir,
> 
> <snip>
>  
>>> +	/* Update partition table control register on all Nest MMUs */
>>> +	opal_nmmu_set_ptcr(-1UL, __pa(partition_tb) | (PATB_SIZE_SHIFT - 12));
>>> +
>>
>> Just wondering if
>>
>> 1. Instead of using -1 for all cpus, we should do
>> 	for_each_online_cpu() {
>> 		opal_numm_set_ptcr(...)
>> 	}
> 
> Good question, but I don't think it makes sense to do that. The NMMU is
> per-chip/socket rather than per-cpu so it shouldn't be tied to
> onlining/offlining of individual CPUs.
> 
>> 2. In cpu hotplug path do the same when onlining and set to NULL on
>> offlining?
> 
> Again, the nmmu isn't tied to a specific CPU but rather a chip/socket. So in
> theory at least it's possible that all CPUs in a chip could be offline but
> other units on the chip could still be using the nmmu so we wouldn't want to
> disable the nmmu at that point.

Fair enough

Balbir Singh.