From mboxrd@z Thu Jan 1 00:00:00 1970 From: vkoul@infradead.org (Vinod Koul) Date: Fri, 09 Sep 2011 03:24:33 +0530 Subject: [PATCH 16/18] dmaengine/ambhe rest oa-pl08x: Add support for sg len greater than one for slave transfers In-Reply-To: References: <5d691ab0c4f447c9f324213d8d740ac61d1739a1.1311936524.git.viresh.kumar@st.com> <20110814083618.GE4986@n2100.arm.linux.org.uk> <4E4CCF7B.8060704@st.com> <20110821083306.GA12028@n2100.arm.linux.org.uk> <4E532B19.6000103@st.com> <4E5715CE.2070806@st.com> <4E575E75.40603@st.com> <4E5F594D.10203@st.com> <438BB0150E931F4B9CE701519A4463010871804A4C@bgsmsx502.gar.corp.intel.com> <4E683B74.5000701@st.com> Message-ID: <1315518873.6638.7.camel@vkoul-mobl4> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, 2011-09-08 at 12:29 +0200, Linus Walleij wrote: > On Thu, Sep 8, 2011 at 5:50 AM, Viresh Kumar wrote: > > > If i am getting this clearly, the concern is "why to queue separate transfers for > > individual sg's? Better would be to prepare the complete list at once and > > start the transfer, so that DMA stops only after finishing all sg's > > passed from user." Is this what you are pointing at? > > Yes. > > > If yes, then the same is done in this patch too. An array for llis is allocated at > > the start, then for each sg i prepare lli list from this array. Last lli from one sg > > is followed by first lli from next sg. And so i get a continuous chain of llis. > > OK so I guess I was lost in the code ... > > So this is mainy cached as txd->dsg_list so you can quickly retrieve the > number of bytes pending in the LLI by traversing that sglist. > > This is better than what the coh901318 does, because that driver > resorts to going into the physical LLIs themselves to retrieve this > info. > > It also seems like this will play nice with Per Forlin's MMC > speed-up patches, so that will become effective for your MMC > usecases. > > Now I really like this patch. > > Sorry for being such a slow learner! > Reviewed-by: Linus Walleij Okay, great. I will check the rest of the series (i think 3 patches) and apply then next week. -- ~Vinod Koul Intel Corp.