linux-kernel - Re: [PATCH] Remove ARM errata Workarounds 458693 and 460075

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Message-ID: <20170416080446.GI17774@n2100.armlinux.org.uk>
Date:   Sun, 16 Apr 2017 09:04:46 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Nisal Menuka <nisalmenuka23@...il.com>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     dianders@...omium.org, kever.yang@...k-chips.com,
        vladimir.murzin@....com, armlinux@...isordat.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Remove ARM errata Workarounds 458693 and 460075

On Sat, Apr 15, 2017 at 07:06:06PM -0500, Nisal Menuka wrote:
> According to ARM, these errata exist only in a version of Cortex-A8
> (r2p0) which was never built. Therefore, I believe there are no platforms
> where this workaround should be enabled.
> link :http://infocenter.arm.com/help/index.jsp?topic=
> /com.arm.doc.faqs/ka15634.html

These were submitted by ARM Ltd back in 2009 - if the silicon was never
built, there would've been no reason to submit them.  Maybe Catalin can
shed some light on this, being the commit author who introduced these?

> Signed-off-by: Nisal Menuka <nisalmenuka23@...il.com>
> ---
>  arch/arm/Kconfig      | 27 ---------------------------
>  arch/arm/mm/proc-v7.S | 14 --------------
>  2 files changed, 41 deletions(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 0d4e71b..d527963 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1005,33 +1005,6 @@ config ARM_ERRATA_430973
>  	  Note that setting specific bits in the ACTLR register may not be
>  	  available in non-secure mode.
>  
> -config ARM_ERRATA_458693
> -	bool "ARM errata: Processor deadlock when a false hazard is created"
> -	depends on CPU_V7
> -	depends on !ARCH_MULTIPLATFORM
> -	help
> -	  This option enables the workaround for the 458693 Cortex-A8 (r2p0)
> -	  erratum. For very specific sequences of memory operations, it is
> -	  possible for a hazard condition intended for a cache line to instead
> -	  be incorrectly associated with a different cache line. This false
> -	  hazard might then cause a processor deadlock. The workaround enables
> -	  the L1 caching of the NEON accesses and disables the PLD instruction
> -	  in the ACTLR register. Note that setting specific bits in the ACTLR
> -	  register may not be available in non-secure mode.
> -
> -config ARM_ERRATA_460075
> -	bool "ARM errata: Data written to the L2 cache can be overwritten with stale data"
> -	depends on CPU_V7
> -	depends on !ARCH_MULTIPLATFORM
> -	help
> -	  This option enables the workaround for the 460075 Cortex-A8 (r2p0)
> -	  erratum. Any asynchronous access to the L2 cache may encounter a
> -	  situation in which recent store transactions to the L2 cache are lost
> -	  and overwritten with stale memory contents from external memory. The
> -	  workaround disables the write-allocate mode for the L2 cache via the
> -	  ACTLR register. Note that setting specific bits in the ACTLR register
> -	  may not be available in non-secure mode.
> -
>  config ARM_ERRATA_742230
>  	bool "ARM errata: DMB operation may be faulty"
>  	depends on CPU_V7 && SMP
> diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
> index d00d52c..43a4a12 100644
> --- a/arch/arm/mm/proc-v7.S
> +++ b/arch/arm/mm/proc-v7.S
> @@ -306,20 +306,6 @@ __ca8_errata:
>  	orreq	r0, r0, #(1 << 6)		@ set IBE to 1
>  	mcreq	p15, 0, r0, c1, c0, 1		@ write aux control register
>  #endif
> -#ifdef CONFIG_ARM_ERRATA_458693
> -	teq	r6, #0x20			@ only present in r2p0
> -	mrceq	p15, 0, r0, c1, c0, 1		@ read aux control register
> -	orreq	r0, r0, #(1 << 5)		@ set L1NEON to 1
> -	orreq	r0, r0, #(1 << 9)		@ set PLDNOP to 1
> -	mcreq	p15, 0, r0, c1, c0, 1		@ write aux control register
> -#endif
> -#ifdef CONFIG_ARM_ERRATA_460075
> -	teq	r6, #0x20			@ only present in r2p0
> -	mrceq	p15, 1, r0, c9, c0, 2		@ read L2 cache aux ctrl register
> -	tsteq	r0, #1 << 22
> -	orreq	r0, r0, #(1 << 22)		@ set the Write Allocate disable bit
> -	mcreq	p15, 1, r0, c9, c0, 2		@ write the L2 cache aux ctrl register
> -#endif
>  	b	__errata_finish
>  
>  __ca9_errata:
> -- 
> 2.7.4
> 

-- 
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