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

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Date:	Thu, 29 Jan 2015 11:34:50 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Wenyou Yang <wenyou.yang@...el.com>
Cc:	nicolas.ferre@...el.com, 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" ?

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