On Fri, 2018-10-05 at 22:56 +0000, Vineet Gupta wrote:
> 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 !
Yes we've run into this.
Remember, we have IOC disabled (actually 'not enabled') in most of HSDK linux demos
(https://github.com/foss-for-synopsys-dwc-arc-processors/buildroot-demos/releases)
So we faced several times that this demos crashes different weird ways when we
accidentally launch them using old u-boot (which enables IOC by default!)
As we don't want to forcibly disable IOC during linux launch
(https://lkml.org/lkml/2018/1/19/557)
I guess panic is what we need here.
> 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 ?
Yes, I prefer to panic early instead of random errors / crashes later.
The problem with warning here is that it isn't very clear / easy to match warning
message with some random error.
> -Vineet
--
Eugeniy Paltsev
