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: <20120426103840.GA6294@arm.com>
Date:	Thu, 26 Apr 2012 11:38:40 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Yilu Mao <ylmao@...vell.com>
Cc:	"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" <njiang1@...vell.com>
Subject: Re: [PATCH] ARM: cache-l2x0.c: save aux ctrl for resume in case
 that l2x0 is enabled before init

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?

-- 
Catalin
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