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Date: Fri, 12 Jul 2019 08:28:00 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Alexey Kardashevskiy <aik@ozlabs.ru>
Subject: Re: [PATCH kernel v4 0/4 repost] powerpc/ioda2: Yet another attempt
 to allow DMA masks between 32 and 59
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Cc: Sam Bobroff <sbobroff@linux.ibm.com>,
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On Fri, Jul 12, 2019 at 07:45:05PM +1000, Alexey Kardashevskiy wrote:
> This is an attempt to allow DMA masks between 32..59 which are not large
> enough to use either a PHB3 bypass mode or a sketchy bypass. Depending
> on the max order, up to 40 is usually available.

Can you elaborate what you man with supported in detail?  In the end
a DMA devices DMA capability is only really interesting as a lower
bound.

e.g. if you have a DMA that supports 40-bit DMA addressing we could
always treat it as if supports 32-bit addressing, and I thought the
powerpc code does that, as the DMA API now relies on that.  Did I miss
something and it explicitly rejected that (in which case I didn't spot
the fix in this series), or is this just an optimization to handle these
devices more optimally, in which case maybe the changelog could be
improved a bit.