Re: [RFC 09/13] iommu/arm-smmu: Make use of dev_64bit_mmio_supported()
From: Robin Murphy <robin.murphy@arm.com>
Date: 2021-03-02 11:22:41
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On 2021-02-26 14:03, Nicolas Saenz Julienne wrote:
quoted hunk ↗ jump to hunk
Some arm SMMU implementations might sit on a bus that doesn't support 64bit memory accesses. In that case default to using hi_lo_{readq, writeq}() and BUG if such platform tries to use AArch64 formats as they rely on writeq()'s atomicity. Signed-off-by: Nicolas Saenz Julienne <redacted> --- drivers/iommu/arm/arm-smmu/arm-smmu.c | 9 +++++++++ drivers/iommu/arm/arm-smmu/arm-smmu.h | 9 +++++++-- 2 files changed, 16 insertions(+), 2 deletions(-)diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c index d8c6bfde6a61..239ff42b20c3 100644 --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c@@ -1889,6 +1889,15 @@ static int arm_smmu_device_cfg_probe(struct arm_smmu_device *smmu) smmu->features |= ARM_SMMU_FEAT_FMT_AARCH64_64K; } + /* + * 64bit accesses not possible through the interconnect, AArch64 + * formats depend on it. + */ + BUG_ON(!dev_64bit_mmio_supported(smmu->dev) && + smmu->features & (ARM_SMMU_FEAT_FMT_AARCH64_4K | + ARM_SMMU_FEAT_FMT_AARCH64_16K | + ARM_SMMU_FEAT_FMT_AARCH64_64K));
No. Crashing the kernel in a probe routine which is free to fail is unacceptable either way, but guaranteeing failure in the case that the workaround *would* be required is doubly so. Basically, this logic is backwards - if you really wanted to handle it generically, this would be the point at which you'd need to actively suppress all the detected hardware features which depend on 64-bit atomicity, not complain about them.
quoted hunk ↗ jump to hunk
+ if (smmu->impl && smmu->impl->cfg_probe) { ret = smmu->impl->cfg_probe(smmu); if (ret)diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.h b/drivers/iommu/arm/arm-smmu/arm-smmu.h index d2a2d1bc58ba..997d13a21717 100644 --- a/drivers/iommu/arm/arm-smmu/arm-smmu.h +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.h@@ -477,15 +477,20 @@ static inline void arm_smmu_writel(struct arm_smmu_device *smmu, int page, { if (smmu->impl && unlikely(smmu->impl->write_reg)) smmu->impl->write_reg(smmu, page, offset, val); - else + else if (dev_64bit_mmio_supported(smmu->dev)) writel_relaxed(val, arm_smmu_page(smmu, page) + offset); + else + hi_lo_writeq_relaxed(val, arm_smmu_page(smmu, page) + offset);
As Arnd pointed out, this is in completely the wrong place. Also, in general it doesn't work if the implementation already needs a hook to filter or override register accesses for any other reason. TBH I'm not convinced that this isn't *more* of a mess than handling it on a SoC-specific basis... Robin.
}
static inline u64 arm_smmu_readq(struct arm_smmu_device *smmu, int page, int offset)
{
if (smmu->impl && unlikely(smmu->impl->read_reg64))
return smmu->impl->read_reg64(smmu, page, offset);
- return readq_relaxed(arm_smmu_page(smmu, page) + offset);
+ else if (dev_64bit_mmio_supported(smmu->dev))
+ return readq_relaxed(arm_smmu_page(smmu, page) + offset);
+ else
+ return hi_lo_readq_relaxed(arm_smmu_page(smmu, page) + offset);
}
static inline void arm_smmu_writeq(struct arm_smmu_device *smmu, int page,_______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel