From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Fri, 28 Feb 2014 16:24:56 +0100 Subject: [PATCH v2 4/7] dma: of: introduce of_dma_is_coherent() helper In-Reply-To: References: <1393535872-20915-1-git-send-email-santosh.shilimkar@ti.com> <10040083.PbPEQQPCjl@wuerfel> Message-ID: <5773663.p5fEFmy536@wuerfel> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Friday 28 February 2014 09:14:19 Rob Herring wrote: > > I know Will D was not a fan of this property. Primarily I believe > because you may need to describe more than just a boolean in more > complex bus topologies. I can't think of any example where it's not per-device. Do you think we can end up with a device that has multiple bus master ports, only some of which are coherent, or is there a different concern? > Effectively, highbank is always coherent. It was only PCI that is > non-coherent, but I can safely say PCI will never be enabled at this > point. There are no designs with PCI beyond 1 or 2 validation boards > (total boards, not designs), and getting PCI to work was quite hacky > due to only a 1MB window. The other masters are programmable, but only > the coherent path is used as the non-coherent path actually has some > issues. I had expected the opposite believing the ACP port would > actually have issues which is also why I made it configurable. Ok, I see. I still expect that we will see systems that are only partially coherent in the future, but it's good to know we don't really have to deal with backwards-compatibility as long as we can just hardcode highbank to be always coherent. I'm especially thankful we don't have to deal with the PCI implementation. Arnd