linux-kernel - Re: [PATCH v2 11/11] ARC: [plat-eznps] Handle memory error as an exception

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Date:   Fri, 2 Jun 2017 12:04:25 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Noam Camus <noamca@...lanox.com>,
        <linux-snps-arc@...ts.infradead.org>
CC:     <linux-kernel@...r.kernel.org>, Elad Kanfi <eladkan@...lanox.com>
Subject: Re: [PATCH v2 11/11] ARC: [plat-eznps] Handle memory error as an
 exception

On 05/27/2017 11:52 PM, Noam Camus wrote:
> From: Noam Camus <noamca@...lanox.com>
> 
> This commit adds the configuration CONFIG_EZNPS_MEM_ERROR.
> If set, it will cause the kernel to handle user memory error
> as a machine check exception.
> It is required in order to align the NPS simulator memory
> error handling to the one of the NPS400 real chip behavior.
> We override weak symbole of mem_service to achieve that.
> 
> Signed-off-by: Elad Kanfi <eladkan@...lanox.com>
> Signed-off-by: Noam Camus <noamca@...lanox.com>
> ---
>   arch/arc/plat-eznps/Kconfig |   11 +++++++++++
>   arch/arc/plat-eznps/entry.S |   14 ++++++++++++++
>   2 files changed, 25 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/arc/plat-eznps/Kconfig b/arch/arc/plat-eznps/Kconfig
> index feaa471..c5f946c 100644
> --- a/arch/arc/plat-eznps/Kconfig
> +++ b/arch/arc/plat-eznps/Kconfig
> @@ -32,3 +32,14 @@ config EZNPS_MTM_EXT
>   	  any of them seem like CPU from Linux point of view.
>   	  All threads within same core share the execution unit of the
>   	  core and HW scheduler round robin between them.
> +
> +config EZNPS_MEM_ERROR
> +       bool "ARC-EZchip Memory error as an exception"
> +       depends on ARC_PLAT_EZNPS
> +       default n
> +       help
> +         On the real chip of the NPS, user memory errors are handled
> +         as a machine check exception, whereas on simulator platform
> +         for NPS, it handled as an interrupt level 2 (like legacy arc
> +         real chip architecture).This configuration will cause the kernel
> +         to handle memory error as a machine check exception.

Do you really need a Kconfig option here. AFAIKR you guys had some magic in 
platform code to determine whether running on sim or hw - can that be not used ?

> diff --git a/arch/arc/plat-eznps/entry.S b/arch/arc/plat-eznps/entry.S
> index 328261c..03e2892 100644
> --- a/arch/arc/plat-eznps/entry.S
> +++ b/arch/arc/plat-eznps/entry.S
> @@ -68,3 +68,17 @@ ENTRY(res_service)
>   
>   	j	stext
>   END(res_service)
> +
> +#if defined(CONFIG_EZNPS_MEM_ERROR)
> +ENTRY(mem_service)
> +	; SW workaround to cover up on a difference between
> +	; NPS real chip and simulator behaviors.
> +	; NPS real chip will activate a machine check exception
> +	; in case of memory error, while the simulator will
> +	; trigger a level 2 interrupt. Therefor this code section
> +	; should be reached only in simulation mode.
> +	; DEAD END: display Regs and HALT
> +
> +	j EV_MachineCheck
> +END(mem_service)
> +#endif


Just squash the weak symbol patch in here - not worth a separate patch !

-Vineet