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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Message-ID: <4F9924FB.7070308@marvell.com>
Date:	Thu, 26 Apr 2012 18:35:39 +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>, <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 06:28 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.

-- 
Thanks.

Best Wishes,
Yilu Mao
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