From mboxrd@z Thu Jan 1 00:00:00 1970 From: Randy Dunlap Date: Tue, 21 Aug 2007 20:05:15 +0000 Subject: Re: [PATCH 2/3] dma: override "dma_flags_set_dmaflush" for sn-ia64 Message-Id: <20070821130515.6e745b17.randy.dunlap@oracle.com> List-Id: References: <20070818002746.GU1813@sgi.com> <46C94FD5.6000006@sgi.com> <20070821193522.GD5592@sgi.com> In-Reply-To: <20070821193522.GD5592@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: akepner@sgi.com Cc: Jes Sorensen , linux-kernel , rdreier@cisco.com, linux-ia64 , James.Bottomley@HansenPartnership.com On Tue, 21 Aug 2007 12:35:22 -0700 akepner@sgi.com wrote: > > > I'm a little concerned about changing the API for the dma_ foo > > functions, which are defined cross platform. If you want to change > > that, I think it will require updating the documentation explaining > > it..... > > What do you think of the following? (And is there anyone else > I should be cc-ing for review?) probably the document's author (cc added) > Document semantics of dma_flags_set_dmaflush() > > Signed-off-by: Arthur Kepner > -- > DMA-API.txt | 22 ++++++++++++++++++++++ > 1 files changed, 22 insertions(+) > > diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt > index cc7a8c3..e117b72 100644 > --- a/Documentation/DMA-API.txt > +++ b/Documentation/DMA-API.txt > @@ -392,6 +392,28 @@ Notes: You must do this: > > See also dma_map_single(). > > +int > +dma_flags_set_dmaflush(int dir) > + > +Amend dir (one of the enum dma_data_direction values), with a platform- no comma. > +specific "dmaflush" attribute. Unless the platform supports "posted DMA" add comma after "posted DMA" and drop lots of trailing spaces. > +this is a no-op. > + > +On platforms that support posted DMA, dma_flags_set_dmaflush() causes > +device writes to the associated memory region to flush in-flight DMA. > +This can be important, for example, when (DMA) writes to the memory > +region indicate that DMA of data is complete. If DMA of data and DMA of > +the completion indication race, as they can do when the platform supports > +posted DMA, then the completion indication may arrive in host memory > +ahead of some data. > + > +To prevent this, you might map the memory region used for completion > +indications as follows: > + > + int count, flags = dma_flags_set_dmaflush(DMA_BIDIRECTIONAL); > + ..... > + count = dma_map_sg(dev, sglist, nents, flags); > + > > Part II - Advanced dma_ usage > ----------------------------- > -- > Arthur --- ~Randy *** Remember to use Documentation/SubmitChecklist when testing your code ***