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SubjectRe: [PATCH] ARC: IOC: panic if kernel was started with previously enabled IOC
Date
On 10/04/2018 06:12 AM, Eugeniy Paltsev wrote:
>
> diff --git a/arch/arc/mm/cache.c b/arch/arc/mm/cache.c
> index f2701c13a66b..ee7b63e9c5e3 100644
> --- a/arch/arc/mm/cache.c
> +++ b/arch/arc/mm/cache.c
> @@ -1144,6 +1144,25 @@ noinline void __init arc_ioc_setup(void)
> {
> unsigned int ioc_base, mem_sz;
>
> + /*
> + * Disabling and reconfiguring of IOC are quite a tricky actions because
> + * nobody knows what happens if there're IOC-ahndled tarnsactions in
> + * flight when we're disabling IOC.
> + *
> + * And the problem is external DMA masters [that were initialized and
> + * set in a bootlaoder that was executed before we got here] might
> + * continue to send data to memory even at this point and we have
> + * no way to prevent that.
> + *
> + * That said it's much safer to not enable IOC at all anywhere before
> + * Linux kernel.
> + */
> + if (read_aux_reg(ARC_REG_IO_COH_ENABLE) & ARC_IO_COH_ENABLE_BIT)
> + panic("kernel was started with previously enabled IOC!\n");

While I understand the needs, this seems excessive, should we warm the user,
instead of panic ? Did you run into specific issue to warrant this !

OTOH in recent past more than 1 person ran into some hsdk uboot shenanigans, where
we had to upgrade the uboot to get it working with prebuit images - is that what
you are trying to prevent here - panic early instead of random user errors / hangs
later ?

-Vineet

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