Re: [PATCH RFC 13/19] iommu/arm-smmu-v3: Add feature detection for BBML

[Robin Murphy <robin.murphy@arm.com>]

On 2022-04-28 22:09, Joao Martins wrote:
> From: Kunkun Jiang <jiangkunkun@huawei.com>
> 
> This detects BBML feature and if SMMU supports it, transfer BBMLx
> quirk to io-pgtable.
> 
> BBML1 requires still marking PTE nT prior to performing a
> translation table update, while BBML2 requires neither break-before-make
> nor PTE nT bit being set. For dirty tracking it needs to clear
> the dirty bit so checking BBML2 tells us the prerequisite. See SMMUv3.2
> manual, section "3.21.1.3 When SMMU_IDR3.BBML == 2 (Level 2)" and
> "3.21.1.2 When SMMU_IDR3.BBML == 1 (Level 1)"

You can drop this, and the dependencies on BBML elsewhere, until you get 
round to the future large-page-splitting work, since that's the only 
thing this represents. Not much point having the feature flags without 
an actual implementation, or any users.

Robin.

> Co-developed-by: Keqian Zhu <zhukeqian1@huawei.com>
> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
> Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
> [joaomart: massage commit message with the need to have BBML quirk
>   and add the Quirk io-pgtable flags]
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 19 +++++++++++++++++++
>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  6 ++++++
>   include/linux/io-pgtable.h                  |  3 +++
>   3 files changed, 28 insertions(+)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index 14609ece4e33..4dba53bde2e3 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -2203,6 +2203,11 @@ static int arm_smmu_domain_finalise(struct iommu_domain *domain,
>   		.iommu_dev	= smmu->dev,
>   	};
>   
> +	if (smmu->features & ARM_SMMU_FEAT_BBML1)
> +		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_ARM_BBML1;
> +	else if (smmu->features & ARM_SMMU_FEAT_BBML2)
> +		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_ARM_BBML2;
> +
>   	pgtbl_ops = alloc_io_pgtable_ops(fmt, &pgtbl_cfg, smmu_domain);
>   	if (!pgtbl_ops)
>   		return -ENOMEM;
> @@ -3591,6 +3596,20 @@ static int arm_smmu_device_hw_probe(struct arm_smmu_device *smmu)
>   
>   	/* IDR3 */
>   	reg = readl_relaxed(smmu->base + ARM_SMMU_IDR3);
> +	switch (FIELD_GET(IDR3_BBML, reg)) {
> +	case IDR3_BBML0:
> +		break;
> +	case IDR3_BBML1:
> +		smmu->features |= ARM_SMMU_FEAT_BBML1;
> +		break;
> +	case IDR3_BBML2:
> +		smmu->features |= ARM_SMMU_FEAT_BBML2;
> +		break;
> +	default:
> +		dev_err(smmu->dev, "unknown/unsupported BBM behavior level\n");
> +		return -ENXIO;
> +	}
> +
>   	if (FIELD_GET(IDR3_RIL, reg))
>   		smmu->features |= ARM_SMMU_FEAT_RANGE_INV;
>   
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> index 1487a80fdf1b..e15750be1d95 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> @@ -54,6 +54,10 @@
>   #define IDR1_SIDSIZE			GENMASK(5, 0)
>   
>   #define ARM_SMMU_IDR3			0xc
> +#define IDR3_BBML			GENMASK(12, 11)
> +#define IDR3_BBML0			0
> +#define IDR3_BBML1			1
> +#define IDR3_BBML2			2
>   #define IDR3_RIL			(1 << 10)
>   
>   #define ARM_SMMU_IDR5			0x14
> @@ -644,6 +648,8 @@ struct arm_smmu_device {
>   #define ARM_SMMU_FEAT_E2H		(1 << 18)
>   #define ARM_SMMU_FEAT_HA		(1 << 19)
>   #define ARM_SMMU_FEAT_HD		(1 << 20)
> +#define ARM_SMMU_FEAT_BBML1		(1 << 21)
> +#define ARM_SMMU_FEAT_BBML2		(1 << 22)
>   	u32				features;
>   
>   #define ARM_SMMU_OPT_SKIP_PREFETCH	(1 << 0)
> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
> index c2ebfe037f5d..d7626ca67dbf 100644
> --- a/include/linux/io-pgtable.h
> +++ b/include/linux/io-pgtable.h
> @@ -85,6 +85,9 @@ struct io_pgtable_cfg {
>   	#define IO_PGTABLE_QUIRK_ARM_MTK_EXT	BIT(3)
>   	#define IO_PGTABLE_QUIRK_ARM_TTBR1	BIT(5)
>   	#define IO_PGTABLE_QUIRK_ARM_OUTER_WBWA	BIT(6)
> +	#define IO_PGTABLE_QUIRK_ARM_BBML1      BIT(7)
> +	#define IO_PGTABLE_QUIRK_ARM_BBML2      BIT(8)
> +
>   	unsigned long			quirks;
>   	unsigned long			pgsize_bitmap;
>   	unsigned int			ias;
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