linux-kernel - Re: [PATCH] ARM: cache-l2x0.c: save aux ctrl for resume in case that l2x0 is enabled before init

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Date:	Thu, 26 Apr 2012 18:48:18 +0800
From:	Yilu Mao <ylmao@...vell.com>
To:	Catalin Marinas <catalin.marinas@....com>
CC:	Lu Mao <ylmao@...vell.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"Baohua.Song@....com" <Baohua.Song@....com>,
	"santosh.shilimkar@...com" <santosh.shilimkar@...com>,
	"robherring2@...il.com" <robherring2@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Ning Jiang <njiang1@...vell.com>
Subject: Re: [PATCH] ARM: cache-l2x0.c: save aux ctrl for resume in case that
 l2x0 is enabled before init

On 04/26/2012 06:38 PM, Catalin Marinas wrote:
> On Thu, Apr 26, 2012 at 11:35:39AM +0100, Yilu Mao wrote:
>> On 04/26/2012 06:28 PM, Catalin Marinas wrote:
>>> On Thu, Apr 26, 2012 at 11:09:26AM +0100, Yilu Mao wrote:
>>>> On 04/26/2012 05:44 PM, Catalin Marinas wrote:
>>>>> On Thu, Apr 26, 2012 at 10:25:31AM +0100, Yilu Mao wrote:
>>>>>> On 04/26/2012 04:35 PM, Catalin Marinas wrote:
>>>>>>> On Thu, Apr 26, 2012 at 06:00:09AM +0100, Yilu Mao wrote:
>>>>>>>> On 04/24/2012 04:28 PM, Catalin Marinas wrote:
>>>>>>>>> On Tue, Apr 24, 2012 at 03:41:20AM +0100, Yilu Mao wrote:
>>>>>>>>>> +	l2x0_saved_regs.aux_ctrl = aux;
>>>>>>>>>> +
>>>>>>>>>>       	aux&= aux_mask;
>>>>>>>>>>       	aux |= aux_val;
>>>>>>>>>
>>>>>>>>> I think that's the wrong place to save it, it should be after the
>>>>>>>>> masking was done.
>>>>>>>>>
>>>>>>>>> Anyway, if we cannot write this register in l2x0_init() because the L2
>>>>>>>>> was enabled, do we expect the L2 to be disabled during resume?
>>>>>>>>>
>>>>>>>> Sorry, I don't think so.
>>>>>>>> This is the right place to save it because we must make sure the saved
>>>>>>>> aux_ctrl is the same as what it is set.
>>>>>>>> If we save it after masking was done, the saved value will be different
>>>>>>>> because we can't actually change the real setting.
>>>>>>>
>>>>>>> And since we can't actually change the real setting on the resume path,
>>>>>>> why do we need to save it anyway. Is your L2 cache disabled on the
>>>>>>> resume path but not on the cold boot one?
>>>>>>
>>>>>> We can't change L2 aux ctrl setting when do init because it has been
>>>>>> enabled.
>>>>>
>>>>> This is normally for the case where the kernel running in non-secure
>>>>> mode is not allowed to write the L2 aux ctrl register. Does this
>>>>> permission change with core idle?
>>>>>
>>>> Yes, your understanding of previous mail is right. The L2 is enabled on
>>>> code boot and it is disabled on the resume in our case.
>>>
>>> But the kernel either runs in secure mode or the non-secure access to
>>> this register is allowed.
>>>
>>>> So if we don't have such patch, when core idle exit, L2 cache aux ctrl
>>>> register will be set to 0x0 because l2x0_saved_regs.aux_ctrl is not
>>>> initialized.
>>>
>>> You could still make sure that the mask passed doesn't affect the
>>> original setting and save it after masking.
>>>
>> Do you mean the code is like this:
>> aux = readl_relaxed(l2x0_base + L2X0_AUX_CTRL);
>> aux&= aux_mask;
>> l2x0_saved_regs.aux_ctrl = aux;
>>
>> Then the saved value is not the same as real setting. So the restored
>> value after core idle will not the same as before... This is not what we
>> expected.
>
> My point was that on your platform you pass an aux_mask that is meant to
> change the already set aux_ctlr value. Why do you pass such mask to be
> anything other than ~0UL in this case?
>
Sorry I still can't catch your point...
In our platform, we actually use ~0UL as aux mask.

Anyway, the two arguments, aux_value and aux_mask, are both for changing 
the original value set before kernel bootup. If L2 cache is enabled in 
cold boot, both two arguments are useless because we can't set the 
register. So we must make sure we can restore the original value after 
core idle.

-- 
Thanks.

Best Wishes,
Yilu Mao
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