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 From mboxrd@z Thu Jan 1 00:00:00 1970 From: andreas.herrmann@calxeda.com (Andreas Herrmann) Date: Tue, 8 Oct 2013 17:20:08 +0200 Subject: [PATCH 3/5] iommu/arm-smmu: Introduce stream ID masking In-Reply-To: <20131008151007.GD21189@mudshark.cambridge.arm.com> 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> Message-ID: <20131008152008.GE2935@alberich> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.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