[PATCH] ARM: errata: Workaround for Cortex-A12 erratum 818325

[PATCH] ARM: errata: Workaround for Cortex-A12 erratum 818325

[Kever Yang]

From: Huang Tao <huangtao@rock-chips.com>

On Cortex-A12 (r0p0..r0p1-00lac0-rc11), when a CPU executes a sequence of
two conditional store instructions with opposite condition code and
updating the same register, the system might enter a deadlock if the
second conditional instruction is an UNPREDICTABLE STR or STM
instruction. This workaround setting bit[12] of the Feature Register
prevents the erratum. This bit disables an optimisation applied to a
sequence of 2 instructions that use opposing condition codes.

Signed-off-by: Huang Tao <huangtao@rock-chips.com>
Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
---

 arch/arm/Kconfig      | 13 +++++++++++++
 arch/arm/mm/proc-v7.S | 15 ++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 32cbbd5..4545835 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1245,6 +1245,19 @@ config ARM_ERRATA_773022
 	  loop buffer may deliver incorrect instructions. This
 	  workaround disables the loop buffer to avoid the erratum.
 
+config ARM_ERRATA_818325
+	bool "ARM errata: Execution of an UNPREDICTABLE STR or STM instruction might deadlock"
+	depends on CPU_V7
+	help
+	  This option enables the workaround for the 818325 Cortex-A12
+	  (r0p0..r0p1-00lac0-rc11) erratum. When a CPU executes a sequence of
+	  two conditional store instructions with opposite condition code and
+	  updating the same register, the system might enter a deadlock if the
+	  second conditional instruction is an UNPREDICTABLE STR or STM
+	  instruction. This workaround setting bit[12] of the Feature Register
+	  prevents the erratum. This bit disables an optimisation applied to a
+	  sequence of 2 instructions that use opposing condition codes.
+
 endmenu
 
 source "arch/arm/common/Kconfig"
diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index b5d67db..5ffdf97 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -408,7 +408,20 @@ __v7_setup:
 	mcrle	p15, 0, r10, c1, c0, 1		@ write aux control register
 #endif
 
-4:	mov	r10, #0
+	/* Cortex-A12 Errata */
+4:	ldr	r10, =0x00000c0d		@ Cortex-A12 primary part number
+	teq	r0, r10
+	bne	5f
+#ifdef CONFIG_ARM_ERRATA_818325
+	teq	r6, #0x00			@ present in r0p0
+	teqne	r6, #0x01			@ present in r0p1-00lac0-rc11
+	mrceq	p15, 0, r10, c15, c0, 1		@ read diagnostic register
+	orreq	r10, r10, #1 << 12		@ set bit #12
+	mcreq	p15, 0, r10, c15, c0, 1		@ write diagnostic register
+	isb
+#endif
+
+5:	mov	r10, #0
 	mcr	p15, 0, r10, c7, c5, 0		@ I+BTB cache invalidate
 #ifdef CONFIG_MMU
 	mcr	p15, 0, r10, c8, c7, 0		@ invalidate I + D TLBs
-- 
1.8.3.2

Re: [PATCH] ARM: errata: Workaround for Cortex-A12 erratum 818325

[Kever Yang]

Hi Russell,

I'd value your feedback on this if you have a moment.

I think this will need by rk3288 soc.

Thanks

On 08/18/2014 05:58 PM, Kever Yang wrote:
> From: Huang Tao <huangtao@rock-chips.com>
>
> On Cortex-A12 (r0p0..r0p1-00lac0-rc11), when a CPU executes a sequence of
> two conditional store instructions with opposite condition code and
> updating the same register, the system might enter a deadlock if the
> second conditional instruction is an UNPREDICTABLE STR or STM
> instruction. This workaround setting bit[12] of the Feature Register
> prevents the erratum. This bit disables an optimisation applied to a
> sequence of 2 instructions that use opposing condition codes.
>
> Signed-off-by: Huang Tao <huangtao@rock-chips.com>
> Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
> ---
>
>   arch/arm/Kconfig      | 13 +++++++++++++
>   arch/arm/mm/proc-v7.S | 15 ++++++++++++++-
>   2 files changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 32cbbd5..4545835 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1245,6 +1245,19 @@ config ARM_ERRATA_773022
>   	  loop buffer may deliver incorrect instructions. This
>   	  workaround disables the loop buffer to avoid the erratum.
>   
> +config ARM_ERRATA_818325
> +	bool "ARM errata: Execution of an UNPREDICTABLE STR or STM instruction might deadlock"
> +	depends on CPU_V7
> +	help
> +	  This option enables the workaround for the 818325 Cortex-A12
> +	  (r0p0..r0p1-00lac0-rc11) erratum. When a CPU executes a sequence of
> +	  two conditional store instructions with opposite condition code and
> +	  updating the same register, the system might enter a deadlock if the
> +	  second conditional instruction is an UNPREDICTABLE STR or STM
> +	  instruction. This workaround setting bit[12] of the Feature Register
> +	  prevents the erratum. This bit disables an optimisation applied to a
> +	  sequence of 2 instructions that use opposing condition codes.
> +
>   endmenu
>   
>   source "arch/arm/common/Kconfig"
> diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
> index b5d67db..5ffdf97 100644
> --- a/arch/arm/mm/proc-v7.S
> +++ b/arch/arm/mm/proc-v7.S
> @@ -408,7 +408,20 @@ __v7_setup:
>   	mcrle	p15, 0, r10, c1, c0, 1		@ write aux control register
>   #endif
>   
> -4:	mov	r10, #0
> +	/* Cortex-A12 Errata */
> +4:	ldr	r10, =0x00000c0d		@ Cortex-A12 primary part number
> +	teq	r0, r10
> +	bne	5f
> +#ifdef CONFIG_ARM_ERRATA_818325
> +	teq	r6, #0x00			@ present in r0p0
> +	teqne	r6, #0x01			@ present in r0p1-00lac0-rc11
> +	mrceq	p15, 0, r10, c15, c0, 1		@ read diagnostic register
> +	orreq	r10, r10, #1 << 12		@ set bit #12
> +	mcreq	p15, 0, r10, c15, c0, 1		@ write diagnostic register
> +	isb
> +#endif
> +
> +5:	mov	r10, #0
>   	mcr	p15, 0, r10, c7, c5, 0		@ I+BTB cache invalidate
>   #ifdef CONFIG_MMU
>   	mcr	p15, 0, r10, c8, c7, 0		@ invalidate I + D TLBs

Re: [PATCH] ARM: errata: Workaround for Cortex-A12 erratum 818325

[Will Deacon]

On Mon, Aug 18, 2014 at 10:58:09AM +0100, Kever Yang wrote:
> From: Huang Tao <huangtao@rock-chips.com>
> 
> On Cortex-A12 (r0p0..r0p1-00lac0-rc11), when a CPU executes a sequence of
> two conditional store instructions with opposite condition code and
> updating the same register, the system might enter a deadlock if the
> second conditional instruction is an UNPREDICTABLE STR or STM
> instruction. This workaround setting bit[12] of the Feature Register
> prevents the erratum. This bit disables an optimisation applied to a
> sequence of 2 instructions that use opposing condition codes.
> 
> Signed-off-by: Huang Tao <huangtao@rock-chips.com>
> Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
> ---

The Rk3288 I have advertises itself as an r0p1 Cortex-A12 CPU, so isn't
affected by this issue. Until we have an SoC supported in mainline that
requires this workaround, I don't think we should merge it.

Also, please consider setting these bits in your firmware if possible.
The feature register isn't writable from the non-secure side, so if you
want to use virtualisation you'll need to do this differently.

Will

Re: [PATCH] ARM: errata: Workaround for Cortex-A12 erratum 818325

[Russell King - ARM Linux]

On Tue, Aug 26, 2014 at 11:14:14AM +0100, Will Deacon wrote:
> On Mon, Aug 18, 2014 at 10:58:09AM +0100, Kever Yang wrote:
> > From: Huang Tao <huangtao@rock-chips.com>
> > 
> > On Cortex-A12 (r0p0..r0p1-00lac0-rc11), when a CPU executes a sequence of
> > two conditional store instructions with opposite condition code and
> > updating the same register, the system might enter a deadlock if the
> > second conditional instruction is an UNPREDICTABLE STR or STM
> > instruction. This workaround setting bit[12] of the Feature Register
> > prevents the erratum. This bit disables an optimisation applied to a
> > sequence of 2 instructions that use opposing condition codes.
> > 
> > Signed-off-by: Huang Tao <huangtao@rock-chips.com>
> > Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
> > ---
> 
> The Rk3288 I have advertises itself as an r0p1 Cortex-A12 CPU, so isn't
> affected by this issue. Until we have an SoC supported in mainline that
> requires this workaround, I don't think we should merge it.
> 
> Also, please consider setting these bits in your firmware if possible.
> The feature register isn't writable from the non-secure side, so if you
> want to use virtualisation you'll need to do this differently.

I think we're at the point where we start insisting that workarounds
which are simple enable/disable feature bit operations (in other words,
which can be handled by updating a control register in the firmware or
boot loader) must be done that way, and we are not going to add such
workarounds to the kernel anymore.

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