From: Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org> To: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org> Cc: iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, tchalamarla-M3mlKVOIwJVv6pq1l3V1OdBPR1lH4CV8@public.gmane.org, brian.starkey-5wv7dgnIgG8@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org Subject: Re: [PATCH 6/7] iommu/arm-smmu: Decouple context format from kernel config Date: Mon, 25 Apr 2016 12:02:20 +0100 [thread overview] Message-ID: <20160425110219.GH16065@arm.com> (raw) In-Reply-To: <571A617C.3020102-5wv7dgnIgG8@public.gmane.org> On Fri, Apr 22, 2016 at 06:38:04PM +0100, Robin Murphy wrote: > On 21/04/16 17:30, Will Deacon wrote: > >Hi Robin, > > > >On Wed, Apr 13, 2016 at 06:13:02PM +0100, Robin Murphy wrote: > >>The way the driver currently forces an AArch32 or AArch64 context format > >>based on the kernel config and SMMU architecture version is suboptimal, > >>in that it makes it very hard to support oddball mix-and-match cases > >>like the SMMUv1 64KB supplement, or situations where the reduced table > >>depth of an AArch32 short descriptor context may be desirable under an > >>AArch64 kernel. It also only happens to work on current implementations > >>which do support all the relevant formats. > >> > >>Introduce an explicit notion of context format, so we can manage that > >>independently and get rid of the inflexible #ifdeffery. > > > >Thanks for doing all of this! One comment on the page size stuff: > > > >>+ if (IS_ENABLED(CONFIG_64BIT) || cfg->fmt == ARM_SMMU_CTX_FMT_NONE) { > >>+ switch (PAGE_SIZE) { > >>+ case SZ_64K: > >>+ if (smmu->features & ARM_SMMU_FEAT_FMT_AARCH64_64K) { > >>+ cfg->fmt = ARM_SMMU_CTX_FMT_AARCH64; > >>+ break; > >>+ } /* else fall through */ > >>+ case SZ_16K: > >>+ if (smmu->features & ARM_SMMU_FEAT_FMT_AARCH64_16K) { > >>+ cfg->fmt = ARM_SMMU_CTX_FMT_AARCH64; > >>+ break; > >>+ } /* else fall through */ > >>+ case SZ_4K: > >>+ if (smmu->features & ARM_SMMU_FEAT_FMT_AARCH64_4K) > >>+ cfg->fmt = ARM_SMMU_CTX_FMT_AARCH64; > >>+ } > >>+ } > > > >The io-pgtable code (arm_lpae_restrict_pgsizes) already does something > >*very* similar to this, using the pgsize_bitmap as input. Can you not > >just choose the ARM_SMMU_CTX_FMT_AARCH64 here and set the pgsize_bitmap > >to represent all page sizes supported by the hardware? That way, you should > >end up with the best option coming back from the pgtable code (I do this > >in the v3 driver, fwiw). > > It took a while to come back to me, but the problem is that we can't call > alloc_io_pgtable_ops(fmt...) before choosing either ARM_64_LPAE_Sx or > ARM_32_LPAE_Sx for fmt, but if we commit to 64-bit we'll get stuck later > without the possibility of falling back to AArch32 if it turns out we don't > have a viable AArch64 granule. In what case would you not have a viable AArch64 granule, but the option of falling back to AArch32 makes things work? > Plus we'd have to remove the LPAE page sizes > from the bitmap beforehand in the case we don't support AARCH64_4K lest we > end up with a phantom format the hardware doesn't actually do, and it all > starts getting rather horrible... I'm not following. The io-pgtable code shouldn't give you back a phanton format. Will
WARNING: multiple messages have this Message-ID (diff)
From: will.deacon@arm.com (Will Deacon) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 6/7] iommu/arm-smmu: Decouple context format from kernel config Date: Mon, 25 Apr 2016 12:02:20 +0100 [thread overview] Message-ID: <20160425110219.GH16065@arm.com> (raw) In-Reply-To: <571A617C.3020102@arm.com> On Fri, Apr 22, 2016 at 06:38:04PM +0100, Robin Murphy wrote: > On 21/04/16 17:30, Will Deacon wrote: > >Hi Robin, > > > >On Wed, Apr 13, 2016 at 06:13:02PM +0100, Robin Murphy wrote: > >>The way the driver currently forces an AArch32 or AArch64 context format > >>based on the kernel config and SMMU architecture version is suboptimal, > >>in that it makes it very hard to support oddball mix-and-match cases > >>like the SMMUv1 64KB supplement, or situations where the reduced table > >>depth of an AArch32 short descriptor context may be desirable under an > >>AArch64 kernel. It also only happens to work on current implementations > >>which do support all the relevant formats. > >> > >>Introduce an explicit notion of context format, so we can manage that > >>independently and get rid of the inflexible #ifdeffery. > > > >Thanks for doing all of this! One comment on the page size stuff: > > > >>+ if (IS_ENABLED(CONFIG_64BIT) || cfg->fmt == ARM_SMMU_CTX_FMT_NONE) { > >>+ switch (PAGE_SIZE) { > >>+ case SZ_64K: > >>+ if (smmu->features & ARM_SMMU_FEAT_FMT_AARCH64_64K) { > >>+ cfg->fmt = ARM_SMMU_CTX_FMT_AARCH64; > >>+ break; > >>+ } /* else fall through */ > >>+ case SZ_16K: > >>+ if (smmu->features & ARM_SMMU_FEAT_FMT_AARCH64_16K) { > >>+ cfg->fmt = ARM_SMMU_CTX_FMT_AARCH64; > >>+ break; > >>+ } /* else fall through */ > >>+ case SZ_4K: > >>+ if (smmu->features & ARM_SMMU_FEAT_FMT_AARCH64_4K) > >>+ cfg->fmt = ARM_SMMU_CTX_FMT_AARCH64; > >>+ } > >>+ } > > > >The io-pgtable code (arm_lpae_restrict_pgsizes) already does something > >*very* similar to this, using the pgsize_bitmap as input. Can you not > >just choose the ARM_SMMU_CTX_FMT_AARCH64 here and set the pgsize_bitmap > >to represent all page sizes supported by the hardware? That way, you should > >end up with the best option coming back from the pgtable code (I do this > >in the v3 driver, fwiw). > > It took a while to come back to me, but the problem is that we can't call > alloc_io_pgtable_ops(fmt...) before choosing either ARM_64_LPAE_Sx or > ARM_32_LPAE_Sx for fmt, but if we commit to 64-bit we'll get stuck later > without the possibility of falling back to AArch32 if it turns out we don't > have a viable AArch64 granule. In what case would you not have a viable AArch64 granule, but the option of falling back to AArch32 makes things work? > Plus we'd have to remove the LPAE page sizes > from the bitmap beforehand in the case we don't support AARCH64_4K lest we > end up with a phantom format the hardware doesn't actually do, and it all > starts getting rather horrible... I'm not following. The io-pgtable code shouldn't give you back a phanton format. Will
next prev parent reply other threads:[~2016-04-25 11:02 UTC|newest] Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-04-13 17:12 [PATCH 0/7] arm-smmu: Implementation and context format differentiation Robin Murphy 2016-04-13 17:12 ` Robin Murphy [not found] ` <cover.1460391217.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> 2016-04-13 17:12 ` [PATCH 1/7] iommu/arm-smmu: Differentiate specific implementations Robin Murphy 2016-04-13 17:12 ` Robin Murphy [not found] ` <cc1789284c5efa05514231fa3dede9d1d5f2df18.1460391217.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> 2016-04-13 21:15 ` Chalamarla, Tirumalesh 2016-04-13 21:15 ` Chalamarla, Tirumalesh 2016-04-13 17:12 ` [PATCH 2/7] iommu/arm-smmu: Convert ThunderX workaround to new method Robin Murphy 2016-04-13 17:12 ` Robin Murphy [not found] ` <98b8079ee3ede4427b045214a60ba77f1cb3552c.1460391217.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> 2016-04-13 21:16 ` Chalamarla, Tirumalesh 2016-04-13 21:16 ` Chalamarla, Tirumalesh 2016-04-13 17:12 ` [PATCH 3/7] iommu/arm-smmu: Work around MMU-500 prefetch errata Robin Murphy 2016-04-13 17:12 ` Robin Murphy [not found] ` <0484444b6257bfb6adb68405a72c64fc4fc98142.1460391217.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> 2016-04-21 16:15 ` Will Deacon 2016-04-21 16:15 ` Will Deacon 2016-04-21 16:16 ` Will Deacon 2016-04-21 16:16 ` Will Deacon 2016-04-13 17:13 ` [PATCH 4/7] io-64-nonatomic: Add relaxed accessor variants Robin Murphy 2016-04-13 17:13 ` Robin Murphy [not found] ` <44173fd4e8efd27d670cadc6b30e215243a14099.1460391217.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> 2016-04-21 16:18 ` Will Deacon 2016-04-21 16:18 ` Will Deacon [not found] ` <20160421161859.GK929-5wv7dgnIgG8@public.gmane.org> 2016-04-22 17:08 ` Robin Murphy 2016-04-22 17:08 ` Robin Murphy [not found] ` <571A5A9E.7040305-5wv7dgnIgG8@public.gmane.org> 2016-04-25 13:32 ` Will Deacon 2016-04-25 13:32 ` Will Deacon [not found] ` <20160425133242.GC30830-5wv7dgnIgG8@public.gmane.org> 2016-04-25 15:21 ` Arnd Bergmann 2016-04-25 15:21 ` Arnd Bergmann 2016-04-25 15:28 ` Robin Murphy 2016-04-25 15:28 ` Robin Murphy [not found] ` <571E3781.3070609-5wv7dgnIgG8@public.gmane.org> 2016-04-25 15:41 ` Arnd Bergmann 2016-04-25 15:41 ` Arnd Bergmann 2016-04-25 16:11 ` Will Deacon 2016-04-25 16:11 ` Will Deacon 2016-04-25 16:11 ` Arnd Bergmann 2016-04-25 16:11 ` Arnd Bergmann 2016-04-26 10:38 ` [PATCH v2] " Robin Murphy 2016-04-26 10:38 ` Robin Murphy 2016-04-13 17:13 ` [PATCH 5/7] iommu/arm-smmu: Tidy up 64-bit/atomic I/O accesses Robin Murphy 2016-04-13 17:13 ` Robin Murphy 2016-04-13 17:13 ` [PATCH 6/7] iommu/arm-smmu: Decouple context format from kernel config Robin Murphy 2016-04-13 17:13 ` Robin Murphy [not found] ` <173006777218859d1671ae517c70592c6c02f630.1460391217.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> 2016-04-21 16:30 ` Will Deacon 2016-04-21 16:30 ` Will Deacon [not found] ` <20160421163019.GL929-5wv7dgnIgG8@public.gmane.org> 2016-04-22 17:38 ` Robin Murphy 2016-04-22 17:38 ` Robin Murphy [not found] ` <571A617C.3020102-5wv7dgnIgG8@public.gmane.org> 2016-04-25 11:02 ` Will Deacon [this message] 2016-04-25 11:02 ` Will Deacon [not found] ` <20160425110219.GH16065-5wv7dgnIgG8@public.gmane.org> 2016-04-25 13:14 ` Robin Murphy 2016-04-25 13:14 ` Robin Murphy [not found] ` <571E1851.2030400-5wv7dgnIgG8@public.gmane.org> 2016-04-25 13:41 ` Will Deacon 2016-04-25 13:41 ` Will Deacon [not found] ` <20160425134108.GD30830-5wv7dgnIgG8@public.gmane.org> 2016-04-25 16:21 ` Robin Murphy 2016-04-25 16:21 ` Robin Murphy 2016-04-28 16:12 ` [PATCH v2] " Robin Murphy 2016-04-28 16:12 ` Robin Murphy 2016-04-13 17:13 ` [PATCH 7/7] iommu/arm-smmu: Support SMMUv1 64KB supplement Robin Murphy 2016-04-13 17:13 ` Robin Murphy
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