From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH V11 3/5] i2c: tegra: Add DMA support Date: Wed, 6 Feb 2019 23:16:33 -0800 Message-ID: <20190207071633.GA25149@infradead.org> References: <1549356985-25726-1-git-send-email-skomatineni@nvidia.com> <1549356985-25726-3-git-send-email-skomatineni@nvidia.com> <20190206145343.GA3651@ulmo> <5e66803c-b13b-cb00-e2ff-d096a1650612@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <5e66803c-b13b-cb00-e2ff-d096a1650612@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Dmitry Osipenko Cc: Thierry Reding , Sowjanya Komatineni , jonathanh@nvidia.com, mkarthik@nvidia.com, smohammed@nvidia.com, talho@nvidia.com, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org, linux-i2c@vger.kernel.org List-Id: linux-i2c@vger.kernel.org On Wed, Feb 06, 2019 at 05:56:02PM +0300, Dmitry Osipenko wrote: > > We don't have an IOMMU attached to I2C or APBDMA, so this can't happen > > and even if we had an IOMMU attached, all we care about is the device's > > DMA address space, which means IOVA space, and that would still be > > guaranteed to be contiguous, according to the above. > > Yes, but doesn't T186+ have IOMMU support for the DMA controller? Even if it did, why would that matter? The device would only see IOVA space, the CPU for a normal driver only sees kernel virtual space. Forced contiguous space only makes sense when you have access by CPU physical address, which should not happen for "normal" device drivers.