From: robin.murphy@arm•com (Robin Murphy)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 6/7] iommu/arm-smmu: Decouple context format from kernel config
Date: Fri, 22 Apr 2016 18:38:04 +0100 [thread overview]
Message-ID: <571A617C.3020102@arm.com> (raw)
In-Reply-To: <20160421163019.GL929@arm.com>
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. 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...
Robin.
> Will
>
next prev parent reply other threads:[~2016-04-22 17:38 UTC|newest]
Thread overview: 28+ 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 ` [PATCH 1/7] iommu/arm-smmu: Differentiate specific implementations Robin Murphy
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 21:16 ` Chalamarla, Tirumalesh
2016-04-13 17:12 ` [PATCH 3/7] iommu/arm-smmu: Work around MMU-500 prefetch errata Robin Murphy
2016-04-21 16:15 ` 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
2016-04-21 16:18 ` Will Deacon
2016-04-22 17:08 ` Robin Murphy
2016-04-25 13:32 ` Will Deacon
2016-04-25 15:21 ` Arnd Bergmann
2016-04-25 15:28 ` Robin Murphy
2016-04-25 15:41 ` Arnd Bergmann
2016-04-25 16:11 ` Will Deacon
2016-04-25 16:11 ` Arnd Bergmann
2016-04-26 10:38 ` [PATCH v2] " 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 ` [PATCH 6/7] iommu/arm-smmu: Decouple context format from kernel config Robin Murphy
2016-04-21 16:30 ` Will Deacon
2016-04-22 17:38 ` Robin Murphy [this message]
2016-04-25 11:02 ` Will Deacon
2016-04-25 13:14 ` Robin Murphy
2016-04-25 13:41 ` Will Deacon
2016-04-25 16:21 ` Robin Murphy
2016-04-28 16:12 ` [PATCH v2] " Robin Murphy
2016-04-13 17:13 ` [PATCH 7/7] iommu/arm-smmu: Support SMMUv1 64KB supplement Robin Murphy
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