From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andreas Herrmann Subject: Re: [PATCH 3/5] iommu/arm-smmu: Introduce stream ID masking Date: Tue, 8 Oct 2013 17:20:08 +0200 Message-ID: <20131008152008.GE2935@alberich> References: <1381224444-27303-1-git-send-email-andreas.herrmann@calxeda.com> <1381224444-27303-4-git-send-email-andreas.herrmann@calxeda.com> <20131008151007.GD21189@mudshark.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20131008151007.GD21189-MRww78TxoiP5vMa5CHWGZ34zcgK1vI+I0E9HWUfgJXw@public.gmane.org> 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: Will Deacon Cc: "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , Rob Herring , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" List-Id: iommu@lists.linux-foundation.org On Tue, Oct 08, 2013 at 11:10:07AM -0400, Will Deacon wrote: > On Tue, Oct 08, 2013 at 10:27:22AM +0100, Andreas Herrmann wrote: > > Ie. use a mask based on smr_mask_bits to map all stream IDs of an SMMU > > to one context. > > > > This behaviour is controlled per SMMU node with DT property > > "arm,smmu-mask-stream-ids" and is only allowed if just a single master > > is attached to an SMMU. If the option is specified, all stream-ids > > that are provided in DT for the single master have no relevance. > > > > This is useful/convenient if a master has more than 8 stream-ids or if > > not all stream-ids are known for a master device. > > Hmmm, this really scares me. What's the use-case? I worry about people > inadvertently putting devices into an iommu domain because they happen to be > included in a mask. Your solution seems to be targetting a single master > with lots of IDs -- is this a PCI RC? No, it's the sata device. It has 0xf as smr_mask_bits. But it's just one device and it (usually) should be mapped to one context -- no matter how many StreamIDs are really used. (PCI RC has also 0xf but there it's clear there can be multiple devices and the masking should not be done.) Andreas