linux-kernel - Re: [PATCH] arc: Flush and invalidate caches on start

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Date:   Thu, 31 Aug 2017 09:31:33 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arc: Flush and invalidate caches on start

On 08/31/2017 07:22 AM, Alexey Brodkin wrote:
> This is useful to make sure no stale data exists in caches after bootloaders.
> The worst thing could be some lines of cache were locked in a bootloader
> for example during DDR recalibration and never unlocked. This may lead
> to really unpredictable issues later down the line.
>
> Signed-off-by: Alexey Brodkin <abrodkin@...opsys.com>
> ---
>   arch/arc/kernel/head.S | 16 ++++++++++++++++
>   1 file changed, 16 insertions(+)
>
> diff --git a/arch/arc/kernel/head.S b/arch/arc/kernel/head.S
> index 8b90d25a15cc..04e28b664183 100644
> --- a/arch/arc/kernel/head.S
> +++ b/arch/arc/kernel/head.S
> @@ -34,6 +34,10 @@
>   #endif
>   	sr	r5, [ARC_REG_IC_CTRL]
>   
> +	; Invalidate entire I$
> +	mov	r5, 1
> +	sr	r5, [ARC_REG_IC_IVIC]
> +
>   1:
>   	lr	r5, [ARC_REG_DC_BCR]
>   	breq    r5, 0, 1f		; D$ doesn't exist
> @@ -46,6 +50,18 @@
>   #endif
>   	sr	r5, [ARC_REG_DC_CTRL]
>   
> +	; Flush entire D$
> +	mov	r5, 1
> +	sr	r5, [ARC_REG_DC_FLSH]
> +	; Wait for flush operation to complete
> +1:
> +	lr	r5, [ARC_REG_DC_CTRL]
> +	bbit1	r5, DC_CTRL_FLUSH_STATUS, 1b
> +
> +	; Invalidate entire D$
> +	mov	r5, 1
> +	sr	r5, [ARC_REG_DC_IVDC]
> +

AFAIK uboot already flushes the caches before handing control over to kernel - so 
why do we need it here.
If uboot is locking lines, it needs to fix that and not penalize the general case 
with or w/o uboot !

-Vineet