[PATCH] irqchip: GICv3: ITS: don't assume 64K page size in its_alloc_tables

[Stuart Yoder]

> -----Original Message-----
> From: Marc Zyngier [mailto:marc.zyngier at arm.com]
> Sent: Monday, May 18, 2015 8:23 AM
> To: Yoder Stuart-B08248; tglx at linutronix.de
> Cc: linux-arm-kernel at lists.infradead.org
> Subject: Re: [PATCH] irqchip: GICv3: ITS: don't assume 64K page size in its_alloc_tables
> 
> Hi Stuart,
> 
> On 15/05/15 00:02, Stuart Yoder wrote:
> > its_alloc_tables() needs to account for page sizes other than
> > 64KB.  Without this change, when PAGE_SIZE=4KB its_alloc_tables()
> > gets stuck in an infinite loop.
> >
> > Signed-off-by: Stuart Yoder <stuart.yoder at freescale.com>
> > ---
> >
> > think this should go into 4.1 if at all possible...without it I am
> > unable to boot a 4.1 kernel on the LS2085 SoC
> 
> What you are suggesting here is a effectively a revert of commit
> 790b57a, which would break other implementations.
> 
> Can you please explain the actual issue? I'm failing to see how you end
> up in an infinite loop here (the system page size and the ITS base
> granule should be completely unrelated...).

Here is the problem line:

      val |= (alloc_size / psz) - 1;

In our case:
   alloc_size=16K
   psz=64K

...so (alloc_size / psz) = 0, and thus val becomes -1, and everything
is screwed up.  We get stuck in a loop to retry_baser:

Thanks,
Stuart