From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [RFC v2 4/4] ARM: keystone: dma-coherent with safe fallback Date: Mon, 06 Jun 2016 14:37:24 +0200 Message-ID: <4810162.vDdHVxWF0U@wuerfel> References: <1465183229-24147-1-git-send-email-wmills@ti.com> <5480709.cGbSehIKrE@wuerfel> <20160606114256.GF6831@leverpostej> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <20160606114256.GF6831@leverpostej> Sender: linux-kernel-owner@vger.kernel.org To: Mark Rutland Cc: Bill Mills , rmk+kernel@armlinux.org.uk, t-kristo@ti.com, ssantosh@kernel.org, catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, r-woodruff2@ti.com, devicetree@vger.kernel.org List-Id: devicetree@vger.kernel.org On Monday, June 6, 2016 12:42:56 PM CEST Mark Rutland wrote: > On Mon, Jun 06, 2016 at 11:09:07AM +0200, Arnd Bergmann wrote: > > On Monday, June 6, 2016 9:56:27 AM CEST Mark Rutland wrote: > > > > So far, the assumption has been: > > > > - when running a non-LPAE kernel, keystone is not coherent, and we > > must ignore both the dma-coherent properties in devices and the > > dma-ranges properties in bus nodes. > > I wasn't able to spot if/where that was enforced. Is it possible to boot > Keystone UP, !LPAE? With !LPAE, no devices are coherent, so that should work with both SMP and and UP. Not sure about LPAE with coherent devices on UP, IIRC we had a bug in that configuration on Armada XP, as the memory was not marked as sharable at all there, and ended up not being coherent with DMA masters. My first guess is that uniprocessor mode on keystone has not been tested at all (TI's QA seems to test only a very limited number of configurations), so it may or may not work. Arnd