From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [RFC][PATCH] devicetree: Add master-id-bits property to the iommu device Date: Mon, 15 Sep 2014 04:38:29 +0200 Message-ID: <201409150438.29649.arnd@arndb.de> References: <1410718646-9710-1-git-send-email-Varun.Sethi@freescale.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1410718646-9710-1-git-send-email-Varun.Sethi-KZfg59tc24xl57MIdRCFDg@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: Varun Sethi Cc: Mark.Rutland-5wv7dgnIgG8@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, will.deacon-5wv7dgnIgG8@public.gmane.org, stuart.yoder-KZfg59tc24xl57MIdRCFDg@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: iommu@lists.linux-foundation.org On Sunday 14 September 2014, Varun Sethi wrote: > "master-id-bits" property added to the IOMMU device node. This property can > be used by the IOMMU driver to match relevan bits in the master id expressed > by a DMA master. > > This can be used to mask out certain bits that get added to the device master id > due to IOMMU topology. For example, in case of MMU-500 the TBUID gets appended to > the master id. This prevents sharing of a stream ID, amongst devices which are > connected to different TBUs. > > Signed-off-by: Varun Sethi This seems rather specific to MMU-500. I don't think that most IOMMUs would use the term 'master ID', 'stream ID' or even the general concept, and you don't expand the acronym 'TBU'. I've seen many IOMMUs and I don't even know what that means. Why do you think this is something that is needed to be known at the global level, rather than a property for some individual drivers? Arnd From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Mon, 15 Sep 2014 04:38:29 +0200 Subject: [RFC][PATCH] devicetree: Add master-id-bits property to the iommu device In-Reply-To: <1410718646-9710-1-git-send-email-Varun.Sethi@freescale.com> References: <1410718646-9710-1-git-send-email-Varun.Sethi@freescale.com> Message-ID: <201409150438.29649.arnd@arndb.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Sunday 14 September 2014, Varun Sethi wrote: > "master-id-bits" property added to the IOMMU device node. This property can > be used by the IOMMU driver to match relevan bits in the master id expressed > by a DMA master. > > This can be used to mask out certain bits that get added to the device master id > due to IOMMU topology. For example, in case of MMU-500 the TBUID gets appended to > the master id. This prevents sharing of a stream ID, amongst devices which are > connected to different TBUs. > > Signed-off-by: Varun Sethi This seems rather specific to MMU-500. I don't think that most IOMMUs would use the term 'master ID', 'stream ID' or even the general concept, and you don't expand the acronym 'TBU'. I've seen many IOMMUs and I don't even know what that means. Why do you think this is something that is needed to be known at the global level, rather than a property for some individual drivers? Arnd