Re: Missing operand for tlbie instruction on Power7

2015-10-03 Thread Segher Boessenkool 
On Fri, Oct 02, 2015 at 09:24:46PM -0500, Peter Bergner wrote:
> > > Ok, than we can just zero out r5 for example and use it in tlbie as RS,
> > > right?
> > 
> > That won't assemble _unless_ your assembler is in POWER7 mode.  It also
> > won't do the right thing at run time on older machines.
> 
> Correct, getting this to work on both pre-power7 and power7 and later
> is tricky.  One really horrible hack would be to do:
> 
>   li r0,0
>   tlbie r4,0
> 
> On pre-power7, the "0" will be taken as a zero L operand and on
> power7 and later, it'll be r0, but with a zero value we loaded in
> the insn before.  I know, really ugly. :-)

Hide the "li 0,0" somewhere earlier, and write it as "tlbie 4,0", and
don't write a comment -- we *like* tricky!

It should really be a separate macro define for power7 and 4xx etc.;
and the macro should not be called "tlbia", but something that makes
it obvious at the usage sites that it is in fact a macro; and why a
macro anyway, a function call might be better here?


Segher
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Re: [PATCH 0/5 v2] Fix NVMe driver support on Power with 32-bit DMA

2015-10-03 Thread Christoph Hellwig 
On Sat, Oct 03, 2015 at 06:51:06AM +1000, Benjamin Herrenschmidt wrote:
> On Fri, 2015-10-02 at 13:09 -0700, Nishanth Aravamudan wrote:
> 
> > 1) add a generic dma_get_page_shift implementation that just returns
> > PAGE_SHIFT
> 
> So you chose to return the granularity of the iommu to the driver
> rather than providing a way for the driver to request a specific
> alignment for DMA mappings. Any specific reason ?

At least for NVMe that's the way to go - it allows to set a page set in
the device which should fit the IOMMU page size.
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