From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Ujfalusi Subject: Re: [PATCH 0/7] dmaengine:omap-dma: Linked List transfer for slave_sg Date: Mon, 18 Jul 2016 15:07:57 +0300 Message-ID: <5c538963-ae46-54fc-27bf-dbae81443215@ti.com> References: <20160714124242.7579-1-peter.ujfalusi@ti.com> <20160718103137.GG5783@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20160718103137.GG5783@n2100.arm.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org To: Russell King - ARM Linux Cc: vinod.koul@intel.com, linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-omap@vger.kernel.org, tony@atomide.com List-Id: linux-omap@vger.kernel.org On 07/18/16 13:31, Russell King - ARM Linux wrote: > On Thu, Jul 14, 2016 at 03:42:35PM +0300, Peter Ujfalusi wrote: >> Hi, >> >> The following series with the final patch will add support for sDMA = Linked List >> transfer support. >> Linked List is supported by sDMA in OMAP3630+ (OMAP4/5, dra7 family)= =2E >> If the descriptor load feature is present we can create the descript= ors for each >> SG beforehand and let sDMA to walk them through. >> This way the number of sDMA interrupts the kernel need to handle wil= l drop >> dramatically. >=20 > I suggested this a few years ago, and I was told by TI that there was > no interest to implement this feature as it had very little performan= ce > effect. I can not comment on this... Few years ago I was not involved with the = DMA drivers so I don't have any idea why would anyone object to have the li= nked list (or descriptor load) mode in use whenever it is possible. I was not even aware of the linked list mode of sDMA 3 weeks back, but = while reading the TRM - for the interleaved mode mainly it sounded like a goo= d idea to implement this. Not really sure about the raw performance impact, but for interactivity= it does help. I remember running 'emerge --sync' on BeagleBoard was pain a= s it took hours and the board was mostly unusable during that time. With the= linked list mode the same takes reasonable time and I can still poke around in= the board. > Do I take it that TI have changed their position on this feature? I was not aware of any position on this from TI - as I mentioned I was = not involved with DMA. It could be that the position from 'TI' is still wha= t it was. Or changed. But as I have been asked to look after TI DMA drivers upstream and I believe that the linked list mode is a good thing to hav= e - which is backed by my experiences. My position is that linked list supp= ort is cool. --=20 P=E9ter