[PATCHv4 3/3] ARM: mvebu: implement L2/PCIe deadlock workaround

[thomas.petazzoni@free-electrons.com (Thomas Petazzoni)]

Dear Jason Cooper,

On Fri, 16 May 2014 02:08:51 -0400, Jason Cooper wrote:
> On Thu, May 15, 2014 at 04:59:34PM +0200, Thomas Petazzoni wrote:
> > The Marvell Armada 375 and Armada 38x SOCs, which use the Cortex-A9
> > CPU core, the PL310 cache and the Marvell PCIe hardware block are
> > affected a L2/PCIe deadlock caused by a system erratum when hardware
> > I/O coherency is used.
> > 
> > This deadlock can be avoided by mapping the PCIe memory areas as
> > strongly-ordered (note: MT_UNCACHED is strongly-ordered), and by
> > removing the outer cache sync done in software. This is implemented in
> > this patch by:
> > 
> >  * Registering a custom arch_ioremap_caller function that allows to
> >    make sure PCI memory regions are mapped MT_UNCACHED.
> > 
> >  * Adding at runtime the 'arm,io-coherent' property to the PL310 cache
> >    controller. This cannot be done permanently in the DT, because the
> >    hardware I/O coherency can only be enabled when CONFIG_SMP is
> >    enabled, in the current kernel situation.
> > 
> > Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> > ---
> >  arch/arm/mach-mvebu/coherency.c | 39 +++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 39 insertions(+)
> 
> Applied to mvebu/soc.

Hum, well, I believe it's OK, but notice that I will very likely have
to do a followup patch, because the solution of making all PCI I/O
mappings use the MT_UNCACHED memory type, suggested by Arnd, has not
been accepted by Will Deacon. So very likely I will have to change
again the mach-mvebu/coherency.c code to call a function that makes PCI
I/O mappings MT_UNCACHED specifically for the mach-mvebu platform. But
that can indeed be a followup patch.

Thanks,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com