From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hanjun Guo Subject: Re: [PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s Date: Tue, 25 Oct 2016 23:25:04 +0800 Message-ID: <61bd096a-cc82-43d3-a99b-5b09252b9e7d@linaro.org> References: <5cf1acbf9c42cc99e5cc0dacb50b7a92c3bd0feb.1476702234.git.robin.murphy@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5cf1acbf9c42cc99e5cc0dacb50b7a92c3bd0feb.1476702234.git.robin.murphy-5wv7dgnIgG8@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: Robin Murphy , will.deacon-5wv7dgnIgG8@public.gmane.org, joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org Cc: iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: iommu@lists.linux-foundation.org On 2016/10/17 19:06, Robin Murphy wrote: > We now delay installing our per-bus iommu_ops until we know an SMMU has > successfully probed, as they don't serve much purpose beforehand, and > doing so also avoids fights between multiple IOMMU drivers in a single > kernel. However, the upshot of passing the return value of bus_set_iommu() > back from our probe function is that if there happens to be more than > one SMMUv3 device in a system, the second and subsequent probes will > wind up returning -EBUSY to the driver core and getting torn down again. > > There are essentially 3 cases in which bus_set_iommu() returns nonzero: > 1. The bus already has iommu_ops installed > 2. One of the add_device callbacks from the initial notifier failed > 3. Allocating or installing the notifier itself failed > > The first two are down to devices other than the SMMU in question, so > shouldn't abort an otherwise-successful SMMU probe, whilst the third is > indicative of the kind of catastrophic system failure which isn't going > to get much further anyway. Consequently, there is little harm in > ignoring the return value either way. > > CC: Lorenzo Pieralisi > Signed-off-by: Robin Murphy Tested-by: Hanjun Guo Thanks Hanjun