Re: [PATCH v3 2/4] iommu/arm-smmu: Workaround for Marvell Armada-AP806 SoC erratum #582743

Robin Murphy
2020-07-03T09:03:29Z

On 2020-07-02 21:16, Tomasz Nowicki wrote:
> From: Hanna Hawa <hannah@marvell.com>
>
> Due to erratum #582743, the Marvell Armada-AP806 can't access 64bit to
> ARM SMMUv2 registers.
>
> Provide implementation relevant hooks:
> - split the writeq/readq to two accesses of writel/readl.
> - mask the MMU_IDR2.PTFSv8 fields to not use AArch64 format (but
> only AARCH32_L) since with AArch64 format 32 bits access is not supported.
>
> Note that separate writes/reads to 2 is not problem regards to
> atomicity, because the driver use the readq/writeq while initialize
> the SMMU, report for SMMU fault, and use spinlock in one
> case (iova_to_phys).

The comment about the spinlock seems to be out of date, and TBH that
whole sentence is a bit unclear - how about something like:

"Note that most 64-bit registers like TTBRn can be accessed as two
32-bit halves without issue, and AArch32 format ensures that the
register writes which must be atomic (for TLBI etc.) need only be 32-bit."

> Signed-off-by: Hanna Hawa <hannah@marvell.com>
> Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
> Signed-off-by: Tomasz Nowicki <tn@semihalf.com>
> ---
> Documentation/arm64/silicon-errata.rst | 3 ++
> drivers/iommu/arm-smmu-impl.c | 52 ++++++++++++++++++++++++++
> 2 files changed, 55 insertions(+)
>
> diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst
> index 936cf2a59ca4..157214d3abe1 100644
> --- a/Documentation/arm64/silicon-errata.rst
> +++ b/Documentation/arm64/silicon-errata.rst
> @@ -125,6 +125,9 @@ stable kernels.
> | Cavium | ThunderX2 Core | #219 | CAVIUM_TX2_ERRATUM_219 |
> +----------------+-----------------+-----------------+-----------------------------+
> +----------------+-----------------+-----------------+-----------------------------+
> +| Marvell | ARM-MMU-500 | #582743 | N/A |
> ++----------------+-----------------+-----------------+-----------------------------+
> ++----------------+-----------------+-----------------+-----------------------------+
> | Freescale/NXP | LS2080A/LS1043A | A-008585 | FSL_ERRATUM_A008585 |
> +----------------+-----------------+-----------------+-----------------------------+
> +----------------+-----------------+-----------------+-----------------------------+
> diff --git a/drivers/iommu/arm-smmu-impl.c b/drivers/iommu/arm-smmu-impl.c
> index c75b9d957b70..c1fc5e1b8193 100644
> --- a/drivers/iommu/arm-smmu-impl.c
> +++ b/drivers/iommu/arm-smmu-impl.c
> @@ -147,6 +147,53 @@ static const struct arm_smmu_impl arm_mmu500_impl = {
> .reset = arm_mmu500_reset,
> };
>
> +static u64 mrvl_mmu500_readq(struct arm_smmu_device *smmu, int page, int off)
> +{
> + u64 val;
> +
> + /*
> + * Marvell Armada-AP806 erratum #582743.
> + * Split all the readq to double readl
> + */
> + val = (u64)readl_relaxed(arm_smmu_page(smmu, page) + off + 4) << 32;
> + val |= readl_relaxed(arm_smmu_page(smmu, page) + off);

Even though io-64-nonatomic-hi-lo.h doesn't override readq() etc. for
64-bit builds, you can still use hi_lo_readq_relaxed() directly.

> +
> + return val;
> +}
> +
> +static void mrvl_mmu500_writeq(struct arm_smmu_device *smmu, int page, int off,
> + u64 val)
> +{
> + /*
> + * Marvell Armada-AP806 erratum #582743.
> + * Split all the writeq to double writel
> + */
> + writel_relaxed(upper_32_bits(val), arm_smmu_page(smmu, page) + off + 4);
> + writel_relaxed(lower_32_bits(val), arm_smmu_page(smmu, page) + off);

Similarly, hi_lo_writeq_relaxed().

> +}
> +
> +static u32 mrvl_mmu500_cfg_id2_fixup(u32 id)
> +{
> +
> + /*
> + * Armada-AP806 erratum #582743.
> + * Hide the SMMU_IDR2.PTFSv8 fields to sidestep the AArch64
> + * formats altogether and allow using 32 bits access on the
> + * interconnect.
> + */
> + id &= ~(ARM_SMMU_ID2_PTFS_4K | ARM_SMMU_ID2_PTFS_16K |
> + ARM_SMMU_ID2_PTFS_64K);
> +
> + return id;
> +}
> +
> +static const struct arm_smmu_impl mrvl_mmu500_impl = {
> + .read_reg64 = mrvl_mmu500_readq,
> + .write_reg64 = mrvl_mmu500_writeq,
> + .cfg_id2_fixup = mrvl_mmu500_cfg_id2_fixup,
> + .reset = arm_mmu500_reset,
> +};
> +
>
> struct arm_smmu_device *arm_smmu_impl_init(struct arm_smmu_device *smmu)
> {
> @@ -160,6 +207,11 @@ struct arm_smmu_device *arm_smmu_impl_init(struct arm_smmu_device *smmu)
> */
> switch (smmu->model) {
> case ARM_MMU500:
> + if (of_device_is_compatible(smmu->dev->of_node,

Nit: there's a local "np" variable now.

> + "marvell,ap806-smmu-500")) {
> + smmu->impl = &mrvl_mmu500_impl;
> + return smmu;
> + }

Please put this with the other integration checks below the switch
statement. Yes, it means we'll end up assigning smmu->impl twice for
this particular case, but that's the intended pattern.

Robin.

> smmu->impl = &arm_mmu500_impl;
> break;
> case CAVIUM_SMMUV2:
>