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). >> If the descriptor load feature is present we can create the descriptors for each >> SG beforehand and let sDMA to walk them through. >> This way the number of sDMA interrupts the kernel need to handle will drop >> dramatically. > > 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 performance > 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 linked 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 good 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 as 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 what 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 have - which is backed by my experiences. My position is that linked list support is cool. -- Péter -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
