Re: [GIT PULL] ARC updates for 4.19-rc8

2018-10-09 Thread Greg Kroah-Hartman
On Mon, Oct 08, 2018 at 07:54:50PM +, Vineet Gupta wrote:
> Hi Greg,
> 
> Late in the cycle, but please pull ARC updates. We could have waited for next
> release had it not been for the the clone syscall fix which is stable 
> material.
> 
> Thx,
> -Vineet
> 
> --->
> The following changes since commit 11da3a7f84f19c26da6f86af878298694ede0804:
> 
>   Linux 4.19-rc3 (2018-09-09 17:26:43 -0700)
> 
> are available in the git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/vgupta/arc.git/ 
> tags/arc-4.19-rc8

Now merged, thanks.

greg k-h

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Re: [PATCH] ARC: IOC: panic if kernel was started with previously enabled IOC

2018-10-09 Thread Eugeniy Paltsev
On Fri, 2018-10-05 at 22:56 +, 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
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