Messages in this thread | | | Subject | Re: [PATCH 1/3 v3] dma: document dma_{un}map_{single|sg}_attrs() interface | From | Michael Ellerman <> | Date | Fri, 14 Mar 2008 15:30:29 +1100 |
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On Tue, 2008-03-11 at 18:19 -0700, akepner@sgi.com wrote: > I have a new proposal for the documentation portion of this > patchset. The code changes essentially amount to > s/DMA_ATTR_SYNC_ON_WRITE/DMA_ATTR_BARRIER/ so thought I'd send > just the doc change for comments now. > > The description of the DMA_ATTR_BARRIER is now very short and > generic - no particular architecture is even mentioned. I can add > a sentence or two near the architecture-specific changes in > arch/ia64/sn/pci/pci_dma.c about why the implementation works > on ia64/sn, etc.
I like this better, sorry to keep nitpicking, but just a few comments below ..
> diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt > index e69de29..a4106ec 100644 > --- a/Documentation/DMA-attributes.txt > +++ b/Documentation/DMA-attributes.txt > @@ -0,0 +1,24 @@ > + DMA attributes > + ============== > + > +This document describes the semantics of the DMA attributes that are > +defined in linux/dma-attrs.h. > + > +DMA_ATTR_BARRIER > +---------------- > + > +DMA_ATTR_BARRIER is a barrier attribute for DMA. DMA to a memory > +region with the DMA_ATTR_BARRIER attribute forces all pending DMA > +writes to complete, and thus provides a mechanism to strictly order > +DMA from a device across all intervening busses and bridges. This > +barrier is not specific to a particular type of interconnect, it > +applies to the system as a whole, and so its implementation must > +account for the idiosyncracies of the system all the way from the > +DMA device to memory.
You say a "DMA to a memory region with the DMA_ATTR_BARRIER attribute forces all pending DMA writes to complete". Does it force _all_ DMA writes to complete, or just writes to the region, or just writes coming from devices? What if something is writing to a device?
Does DMA_ATTR_BARRIER have any effect on reads?
cheers
-- Michael Ellerman OzLabs, IBM Australia Development Lab
wwweb: http://michael.ellerman.id.au phone: +61 2 6212 1183 (tie line 70 21183)
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