From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH v2 2/7] dma-mapping: Generalise dma_32bit_limit flag Date: Wed, 25 Jul 2018 13:29:29 +0200 Message-ID: <20180725112929.GA24736@lst.de> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Robin Murphy Cc: gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org, x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, linux-acpi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, sudeep.holla-5wv7dgnIgG8@public.gmane.org, frowand.list-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, hch-jcswGhMUV9g@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: linux-acpi@vger.kernel.org On Mon, Jul 23, 2018 at 11:16:07PM +0100, Robin Murphy wrote: > Whilst the notion of an upstream DMA restriction is most commonly seen > in PCI host bridges saddled with a 32-bit native interface, a more > general version of the same issue can exist on complex SoCs where a bus > or point-to-point interconnect link from a device's DMA master interface > to another component along the path to memory (often an IOMMU) may carry > fewer address bits than the interfaces at both ends nominally support. > In order to properly deal with this, the first step is to expand the > dma_32bit_limit flag into an arbitrary mask. > > To minimise the impact on existing code, we'll make sure to only > consider this new mask valid if set. That makes sense anyway, since a > mask of zero would represent DMA not being wired up at all, and that > would be better handled by not providing valid ops in the first place. > > Signed-off-by: Robin Murphy Looks good, Reviewed-by: Christoph Hellwig From mboxrd@z Thu Jan 1 00:00:00 1970 From: hch@lst.de (Christoph Hellwig) Date: Wed, 25 Jul 2018 13:29:29 +0200 Subject: [PATCH v2 2/7] dma-mapping: Generalise dma_32bit_limit flag In-Reply-To: References: Message-ID: <20180725112929.GA24736@lst.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Jul 23, 2018 at 11:16:07PM +0100, Robin Murphy wrote: > Whilst the notion of an upstream DMA restriction is most commonly seen > in PCI host bridges saddled with a 32-bit native interface, a more > general version of the same issue can exist on complex SoCs where a bus > or point-to-point interconnect link from a device's DMA master interface > to another component along the path to memory (often an IOMMU) may carry > fewer address bits than the interfaces at both ends nominally support. > In order to properly deal with this, the first step is to expand the > dma_32bit_limit flag into an arbitrary mask. > > To minimise the impact on existing code, we'll make sure to only > consider this new mask valid if set. That makes sense anyway, since a > mask of zero would represent DMA not being wired up at all, and that > would be better handled by not providing valid ops in the first place. > > Signed-off-by: Robin Murphy Looks good, Reviewed-by: Christoph Hellwig