linux-kernel - RE: [PATCH v2 3/3] pm: at91: add disable/enable the L1/L2 cache while suspend/resume

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Date:	Fri, 30 Jan 2015 07:32:07 +0000
From:	"Yang, Wenyou" <Wenyou.Yang@...el.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	"Ferre, Nicolas" <Nicolas.FERRE@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"alexandre.belloni@...e-electrons.com" 
	<alexandre.belloni@...e-electrons.com>,
	"sylvain.rochet@...secur.com" <sylvain.rochet@...secur.com>,
	"peda@...ntia.se" <peda@...ntia.se>,
	"sergei.shtylyov@...entembedded.com" 
	<sergei.shtylyov@...entembedded.com>,
	"linux@...im.org.za" <linux@...im.org.za>
Subject: RE: [PATCH v2 3/3] pm: at91: add disable/enable the L1/L2 cache
 while suspend/resume

Hi Russell,

Thank you very much for your suggestion.

I will redo this patch to use the cache helper functions ASAP.

> -----Original Message-----
> From: Russell King - ARM Linux [mailto:linux@....linux.org.uk]
> Sent: Thursday, January 29, 2015 7:35 PM
> To: Yang, Wenyou
> Cc: Ferre, Nicolas; linux-arm-kernel@...ts.infradead.org; linux-
> kernel@...r.kernel.org; alexandre.belloni@...e-electrons.com;
> sylvain.rochet@...secur.com; peda@...ntia.se;
> sergei.shtylyov@...entembedded.com; linux@...im.org.za
> Subject: Re: [PATCH v2 3/3] pm: at91: add disable/enable the L1/L2 cache while
> suspend/resume
> 
> On Wed, Jan 28, 2015 at 10:24:04AM +0800, Wenyou Yang wrote:
> > +	/*
> > +	 * Clean and invalidate the L2 cache.
> > +	 * Common cache-l2x0.c functions can't be used here since it
> > +	 * uses spinlocks. We are out of coherency here with data cache
> > +	 * disabled. The spinlock implementation uses exclusive load/store
> > +	 * instruction which can fail without data cache being enabled.
> > +	 * Because of this, CPU can lead to deadlock.
> 
> We really need to stop needing platforms to create their own L2 handling code.
> Please move this to a helper function in arch/arm/mm/l2c-l...-clean.S, replacing ...
> with the appropriate part for the code fragment.
> 
> > +	 */
> > +	ldr	r1, at91_l2cc_base_addr
> > +	ldr	r2, [r1]
> > +	cmp	r2, #0
> > +	beq	skip_l2disable
> > +	mov	r0, #0xff
> > +	str	r0, [r2, #L2X0_CLEAN_INV_WAY]
> > +wait:
> > +	ldr	r0, [r2, #L2X0_CLEAN_INV_WAY]
> > +	mov	r1, #0xff
> > +	ands	r0, r0, r1
> > +	bne	wait
> > +
> > +	mov	r0, #0
> > +	str	r0, [r2, #L2X0_CTRL]
> > +
> > +l2x_sync:
> > +	ldr	r0, [r2, #L2X0_CACHE_SYNC]
> > +	bic	r0, r0, #0x1
> > +	str	r0, [r2, #L2X0_CACHE_SYNC]
> 
> I wonder whether you've actually read the documentation for this.  You don't need
> to read-modify-write this register.  The C code doesn't even do this.  A write to this
> register is sufficient - a write issues the sync, a read returns the completion status.
> 
> > +sync:
> > +	ldr	r0, [r2, #L2X0_CACHE_SYNC]
> > +	ands	r0, r0, #0x1
> > +	bne	sync
> 
> Moreover, do you actually need this - it depends on the L2C model.  Only
> L2C220 needs to spin waiting for the sync operation to complete.
> 
> Also, are you sure the "clean+invalidate, disable, sync" sequence is correct?
> Should it not be "clean+invalidate, sync, disable" ?
> 
> --
> FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
> according to speedtest.net.

Best Regards,
Wenyou Yang
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