Date:   Mon, 27 Jun 2022 16:09:23 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Janne Grunau <j@...nau.net>, iommu@...ts.linux-foundation.org
Cc:     Konrad Dybcio <konrad.dybcio@...ainline.org>,
        asahi@...ts.linux.dev, Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Hector Martin <marcan@...can.st>,
        Joerg Roedel <joro@...tes.org>,
        Sven Peter <sven@...npeter.dev>, Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/5] iommu/io-pgtable: Move Apple DART support to its
 own file

On 2022-06-21 08:18, Janne Grunau wrote:
> The pte format used by the DARTs found in the Apple M1 (t8103) is not
> fully compatible with io-pgtable-arm. The 24 MSB are used for subpage
> protection (mapping only parts of page) and conflict with the address
> mask. In addition bit 1 is not available for tagging entries but disables
> subpage protection. Subpage protection could be useful to support a CPU
> granule of 4k with the fixed IOMMU page size of 16k.
> 
> The DARTs found on Apple M1 Pro/Max/Ultra use another different pte
> format which is even less compatible. To support an output address size
> of 42 bit the address is shifted down by 4. Subpage protection is
> mandatory and bit 1 signifies uncached mappings used by the display
> controller.
> 
> It would be advantageous to share code for all known Apple DART
> variants to support common features. The page table allocator for DARTs
> is less complex since it uses a two levels of translation table without
> support for huge pages.
> 
> Signed-off-by: Janne Grunau <j@...nau.net>
> 
> ---
> 
> Changes in v3:
> - move APPLE_DART to its own io-pgtable implementation, copied from
>    io-pgtable-arm and simplified
> 
> Changes in v2:
> - add APPLE_DART2 io-pgtable format
> 
>   MAINTAINERS                     |   1 +
>   drivers/iommu/Kconfig           |   1 -
>   drivers/iommu/Makefile          |   2 +-
>   drivers/iommu/io-pgtable-arm.c  |  63 ----
>   drivers/iommu/io-pgtable-dart.c | 580 ++++++++++++++++++++++++++++++++
>   drivers/iommu/io-pgtable.c      |   2 +
>   6 files changed, 584 insertions(+), 65 deletions(-)
>   create mode 100644 drivers/iommu/io-pgtable-dart.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 1fc9ead83d2a..028b7e31e589 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -1848,6 +1848,7 @@ F:	drivers/clk/clk-apple-nco.c
>   F:	drivers/i2c/busses/i2c-pasemi-core.c
>   F:	drivers/i2c/busses/i2c-pasemi-platform.c
>   F:	drivers/iommu/apple-dart.c
> +F:	drivers/iommu/io-pgtable-dart.c
>   F:	drivers/irqchip/irq-apple-aic.c
>   F:	drivers/mailbox/apple-mailbox.c
>   F:	drivers/nvme/host/apple.c
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index c79a0df090c0..ed6d8260f330 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -294,7 +294,6 @@ config APPLE_DART
>   	tristate "Apple DART IOMMU Support"
>   	depends on ARCH_APPLE || (COMPILE_TEST && !GENERIC_ATOMIC64)
>   	select IOMMU_API
> -	select IOMMU_IO_PGTABLE_LPAE

You still need to select the base IO_PGTABLE. FWIW I think that's 
probably the only crucial issue here - lots more comments below, but 
they're primarily things that could all be unpicked later.

>   	default ARCH_APPLE
>   	help
>   	  Support for Apple DART (Device Address Resolution Table) IOMMUs
> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
> index 44475a9b3eea..bd68c93bbd62 100644
> --- a/drivers/iommu/Makefile
> +++ b/drivers/iommu/Makefile
> @@ -29,4 +29,4 @@ obj-$(CONFIG_HYPERV_IOMMU) += hyperv-iommu.o
>   obj-$(CONFIG_VIRTIO_IOMMU) += virtio-iommu.o
>   obj-$(CONFIG_IOMMU_SVA) += iommu-sva-lib.o io-pgfault.o
>   obj-$(CONFIG_SPRD_IOMMU) += sprd-iommu.o
> -obj-$(CONFIG_APPLE_DART) += apple-dart.o
> +obj-$(CONFIG_APPLE_DART) += apple-dart.o io-pgtable-dart.o
> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> index 94ff319ae8ac..d7f5e23da643 100644
> --- a/drivers/iommu/io-pgtable-arm.c
> +++ b/drivers/iommu/io-pgtable-arm.c
> @@ -130,9 +130,6 @@
>   #define ARM_MALI_LPAE_MEMATTR_IMP_DEF	0x88ULL
>   #define ARM_MALI_LPAE_MEMATTR_WRITE_ALLOC 0x8DULL
>   
> -#define APPLE_DART_PTE_PROT_NO_WRITE (1<<7)
> -#define APPLE_DART_PTE_PROT_NO_READ (1<<8)
> -
>   /* IOPTE accessors */
>   #define iopte_deref(pte,d) __va(iopte_to_paddr(pte, d))
>   
> @@ -406,15 +403,6 @@ static arm_lpae_iopte arm_lpae_prot_to_pte(struct arm_lpae_io_pgtable *data,
>   {
>   	arm_lpae_iopte pte;
>   
> -	if (data->iop.fmt == APPLE_DART) {
> -		pte = 0;
> -		if (!(prot & IOMMU_WRITE))
> -			pte |= APPLE_DART_PTE_PROT_NO_WRITE;
> -		if (!(prot & IOMMU_READ))
> -			pte |= APPLE_DART_PTE_PROT_NO_READ;
> -		return pte;
> -	}
> -
>   	if (data->iop.fmt == ARM_64_LPAE_S1 ||
>   	    data->iop.fmt == ARM_32_LPAE_S1) {
>   		pte = ARM_LPAE_PTE_nG;
> @@ -1107,52 +1095,6 @@ arm_mali_lpae_alloc_pgtable(struct io_pgtable_cfg *cfg, void *cookie)
>   	return NULL;
>   }
>   
> -static struct io_pgtable *
> -apple_dart_alloc_pgtable(struct io_pgtable_cfg *cfg, void *cookie)
> -{
> -	struct arm_lpae_io_pgtable *data;
> -	int i;
> -
> -	if (cfg->oas > 36)
> -		return NULL;
> -
> -	data = arm_lpae_alloc_pgtable(cfg);
> -	if (!data)
> -		return NULL;
> -
> -	/*
> -	 * The table format itself always uses two levels, but the total VA
> -	 * space is mapped by four separate tables, making the MMIO registers
> -	 * an effective "level 1". For simplicity, though, we treat this
> -	 * equivalently to LPAE stage 2 concatenation at level 2, with the
> -	 * additional TTBRs each just pointing at consecutive pages.
> -	 */
> -	if (data->start_level < 1)
> -		goto out_free_data;
> -	if (data->start_level == 1 && data->pgd_bits > 2)
> -		goto out_free_data;
> -	if (data->start_level > 1)
> -		data->pgd_bits = 0;
> -	data->start_level = 2;
> -	cfg->apple_dart_cfg.n_ttbrs = 1 << data->pgd_bits;
> -	data->pgd_bits += data->bits_per_level;
> -
> -	data->pgd = __arm_lpae_alloc_pages(ARM_LPAE_PGD_SIZE(data), GFP_KERNEL,
> -					   cfg);
> -	if (!data->pgd)
> -		goto out_free_data;
> -
> -	for (i = 0; i < cfg->apple_dart_cfg.n_ttbrs; ++i)
> -		cfg->apple_dart_cfg.ttbr[i] =
> -			virt_to_phys(data->pgd + i * ARM_LPAE_GRANULE(data));
> -
> -	return &data->iop;
> -
> -out_free_data:
> -	kfree(data);
> -	return NULL;
> -}
> -
>   struct io_pgtable_init_fns io_pgtable_arm_64_lpae_s1_init_fns = {
>   	.alloc	= arm_64_lpae_alloc_pgtable_s1,
>   	.free	= arm_lpae_free_pgtable,
> @@ -1178,11 +1120,6 @@ struct io_pgtable_init_fns io_pgtable_arm_mali_lpae_init_fns = {
>   	.free	= arm_lpae_free_pgtable,
>   };
>   
> -struct io_pgtable_init_fns io_pgtable_apple_dart_init_fns = {
> -	.alloc	= apple_dart_alloc_pgtable,
> -	.free	= arm_lpae_free_pgtable,
> -};
> -
>   #ifdef CONFIG_IOMMU_IO_PGTABLE_LPAE_SELFTEST
>   
>   static struct io_pgtable_cfg *cfg_cookie __initdata;
> diff --git a/drivers/iommu/io-pgtable-dart.c b/drivers/iommu/io-pgtable-dart.c
> new file mode 100644
> index 000000000000..0c5222942c65
> --- /dev/null
> +++ b/drivers/iommu/io-pgtable-dart.c
> @@ -0,0 +1,580 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Apple DART page table allocator.
> + *
> + * Copyright (C) 2022 The Asahi Linux Contributors
> + *
> + * Based on io-pgtable-arm.
> + *
> + * Copyright (C) 2014 ARM Limited
> + *
> + * Author: Will Deacon <will.deacon@....com>
> + */
> +
> +#define pr_fmt(fmt)	"dart io-pgtable: " fmt
> +
> +#include <linux/atomic.h>
> +#include <linux/bitops.h>
> +#include <linux/io-pgtable.h>
> +#include <linux/kernel.h>
> +#include <linux/sizes.h>
> +#include <linux/slab.h>
> +#include <linux/types.h>
> +
> +#include <asm/barrier.h>
> +
> +#define DART_MAX_ADDR_BITS		52

Surely 36, no?

> +#define DART_MAX_LEVELS		3

It might be simpler in the long run to drop the awkward pretence and 
handle these in their "native" form of multiple 2-level tables.

> +
> +/* Struct accessors */
> +#define io_pgtable_to_data(x)						\
> +	container_of((x), struct dart_io_pgtable, iop)
> +
> +#define io_pgtable_ops_to_data(x)					\
> +	io_pgtable_to_data(io_pgtable_ops_to_pgtable(x))
> +
> +/*
> + * Calculate the right shift amount to get to the portion describing level l
> + * in a virtual address mapped by the pagetable in d.
> + */
> +#define DART_LVL_SHIFT(l, d)						\
> +	(((DART_MAX_LEVELS - (l)) * (d)->bits_per_level) +		\
> +	ilog2(sizeof(dart_iopte)))
> +
> +#define DART_GRANULE(d)						\
> +	(sizeof(dart_iopte) << (d)->bits_per_level)
> +#define DART_PGD_SIZE(d)					\
> +	(sizeof(dart_iopte) << (d)->pgd_bits)
> +
> +#define DART_PTES_PER_TABLE(d)					\
> +	(DART_GRANULE(d) >> ilog2(sizeof(dart_iopte)))
> +
> +/*
> + * Calculate the index at level l used to map virtual address a using the
> + * pagetable in d.
> + */
> +#define DART_PGD_IDX(l, d)						\
> +	((l) == (d)->start_level ? (d)->pgd_bits - (d)->bits_per_level : 0)
> +
> +#define DART_LVL_IDX(a, l, d)						\
> +	(((u64)(a) >> DART_LVL_SHIFT(l, d)) &				\
> +	 ((1 << ((d)->bits_per_level + DART_PGD_IDX(l, d))) - 1))
> +
> +/* Calculate the block/page mapping size at level l for pagetable in d. */
> +#define DART_BLOCK_SIZE(l, d)	(1ULL << DART_LVL_SHIFT(l, d))

If you don't actually have block mappings, much of the above is really 
more complicated than you need.

> +
> +#define APPLE_DART1_PADDR_MASK	GENMASK_ULL(35, 12)
> +
> +/* Apple DART1 protection bits */
> +#define APPLE_DART1_PTE_PROT_NO_READ	BIT(8)
> +#define APPLE_DART1_PTE_PROT_NO_WRITE	BIT(7)
> +#define APPLE_DART1_PTE_PROT_SP_DIS	BIT(1)
> +
> +/* marks PTE as valid */
> +#define APPLE_DART_PTE_VALID		BIT(0)
> +
> +/* IOPTE accessors */
> +#define iopte_deref(pte, d) __va(iopte_to_paddr(pte, d))
> +
> +struct dart_io_pgtable {
> +	struct io_pgtable	iop;
> +
> +	int			pgd_bits;
> +	int			start_level;

If you don't have a variable number of levels, this is a constant.

> +	int			bits_per_level;
> +
> +	void			*pgd;
> +};
> +
> +typedef u64 dart_iopte;
> +
> +static inline bool iopte_leaf(dart_iopte pte, int lvl,
> +			      enum io_pgtable_fmt fmt)
> +{
> +	return (lvl == (DART_MAX_LEVELS - 1)) && (pte & APPLE_DART_PTE_VALID);
> +}
> +
> +static dart_iopte paddr_to_iopte(phys_addr_t paddr,
> +				     struct dart_io_pgtable *data)
> +{
> +	return paddr & APPLE_DART1_PADDR_MASK;
> +}
> +
> +static phys_addr_t iopte_to_paddr(dart_iopte pte,
> +				  struct dart_io_pgtable *data)
> +{
> +	return pte & APPLE_DART1_PADDR_MASK;
> +}
> +
> +static void *__dart_alloc_pages(size_t size, gfp_t gfp,
> +				    struct io_pgtable_cfg *cfg)
> +{
> +	struct device *dev = cfg->iommu_dev;
> +	int order = get_order(size);
> +	struct page *p;
> +
> +	VM_BUG_ON((gfp & __GFP_HIGHMEM));
> +	p = alloc_pages_node(dev ? dev_to_node(dev) : NUMA_NO_NODE,
> +			     gfp | __GFP_ZERO, order);
> +	if (!p)
> +		return NULL;
> +
> +	return page_address(p);
> +}
> +
> +static void __dart_free_pages(void *pages, size_t size)
> +{
> +	free_pages((unsigned long)pages, get_order(size));
> +}
> +
> +static void __dart_init_pte(struct dart_io_pgtable *data,
> +				phys_addr_t paddr, dart_iopte prot,
> +				int lvl, int num_entries, dart_iopte *ptep)
> +{
> +	dart_iopte pte = prot;
> +	size_t sz = DART_BLOCK_SIZE(lvl, data);
> +	int i;
> +
> +	if (lvl == DART_MAX_LEVELS - 1)
> +		pte |= APPLE_DART1_PTE_PROT_SP_DIS;
> +
> +	pte |= APPLE_DART_PTE_VALID;
> +
> +	for (i = 0; i < num_entries; i++)
> +		ptep[i] = pte | paddr_to_iopte(paddr + i * sz, data);
> +}
> +
> +static int dart_init_pte(struct dart_io_pgtable *data,
> +			     unsigned long iova, phys_addr_t paddr,
> +			     dart_iopte prot, int lvl, int num_entries,
> +			     dart_iopte *ptep)
> +{
> +	int i;
> +
> +	for (i = 0; i < num_entries; i++)
> +		if (iopte_leaf(ptep[i], lvl, data->iop.fmt)) {
> +			/* We require an unmap first */
> +			WARN_ON(iopte_leaf(ptep[i], lvl, data->iop.fmt));
> +			return -EEXIST;
> +		}
> +
> +	__dart_init_pte(data, paddr, prot, lvl, num_entries, ptep);
> +	return 0;
> +}
> +
> +static dart_iopte dart_install_table(dart_iopte *table,
> +					     dart_iopte *ptep,
> +					     dart_iopte curr,
> +					     struct dart_io_pgtable *data)
> +{
> +	dart_iopte old, new;
> +
> +	new = paddr_to_iopte(__pa(table), data) | APPLE_DART_PTE_VALID;
> +
> +	/*
> +	 * Ensure the table itself is visible before its PTE can be.
> +	 * Whilst we could get away with cmpxchg64_release below, this
> +	 * doesn't have any ordering semantics when !CONFIG_SMP.
> +	 */
> +	dma_wmb();
> +
> +	old = cmpxchg64_relaxed(ptep, curr, new);
> +
> +	return old;
> +}
> +
> +static int __dart_map(struct dart_io_pgtable *data, unsigned long iova,
> +			  phys_addr_t paddr, size_t size, size_t pgcount,
> +			  dart_iopte prot, int lvl, dart_iopte *ptep,
> +			  gfp_t gfp, size_t *mapped)
> +{
> +	dart_iopte *cptep, pte;
> +	size_t block_size = DART_BLOCK_SIZE(lvl, data);
> +	size_t tblsz = DART_GRANULE(data);
> +	struct io_pgtable_cfg *cfg = &data->iop.cfg;
> +	int ret = 0, num_entries, max_entries, map_idx_start;
> +
> +	/* Find our entry at the current level */
> +	map_idx_start = DART_LVL_IDX(iova, lvl, data);
> +	ptep += map_idx_start;
> +
> +	/* If we can install a leaf entry at this level, then do so */
> +	if (size == block_size) {

It's a bit confusing to retain this logic when it's reduced to a rather 
long-winded obfuscatiuon of "if (lvl == 2)".

> +		max_entries = DART_PTES_PER_TABLE(data) - map_idx_start;
> +		num_entries = min_t(int, pgcount, max_entries);
> +		ret = dart_init_pte(data, iova, paddr, prot, lvl, num_entries, ptep);
> +		if (!ret && mapped)
> +			*mapped += num_entries * size;
> +
> +		return ret;
> +	}
> +
> +	/* We can't allocate tables at the final level */
> +	if (WARN_ON(lvl >= DART_MAX_LEVELS - 1))
> +		return -EINVAL;
> +
> +	/* Grab a pointer to the next level */
> +	pte = READ_ONCE(*ptep);
> +	if (!pte) {
> +		cptep = __dart_alloc_pages(tblsz, gfp, cfg);
> +		if (!cptep)
> +			return -ENOMEM;
> +
> +		pte = dart_install_table(cptep, ptep, 0, data);
> +		if (pte)
> +			__dart_free_pages(cptep, tblsz);
> +	}
> +
> +	if (pte && !iopte_leaf(pte, lvl, data->iop.fmt)) {
> +		cptep = iopte_deref(pte, data);
> +	} else if (pte) {
> +		/* We require an unmap first */
> +		WARN_ON(pte);

Similarly, you can't ever even get here, since the iopte_leaf() above 
can never be true. It would be significantly simpler to swap the two 
halves of this function and lose the recursion. The things you need to 
do at each level - resolve the pgd, look up or allocate the l1 table, 
install the l2 pte - have almost no functional overlap, so simple 
procedural code would be far more suitable.

> +		return -EEXIST;
> +	}
> +
> +	/* Rinse, repeat */
> +	return __dart_map(data, iova, paddr, size, pgcount, prot, lvl + 1,
> +			      cptep, gfp, mapped);
> +}
> +
> +static dart_iopte dart_prot_to_pte(struct dart_io_pgtable *data,
> +					   int prot)
> +{
> +	dart_iopte pte = 0;
> +
> +	if (!(prot & IOMMU_WRITE))
> +		pte |= APPLE_DART1_PTE_PROT_NO_WRITE;
> +	if (!(prot & IOMMU_READ))
> +		pte |= APPLE_DART1_PTE_PROT_NO_READ;
> +
> +	return pte;
> +}
> +
> +static int dart_map_pages(struct io_pgtable_ops *ops, unsigned long iova,
> +			      phys_addr_t paddr, size_t pgsize, size_t pgcount,
> +			      int iommu_prot, gfp_t gfp, size_t *mapped)
> +{
> +	struct dart_io_pgtable *data = io_pgtable_ops_to_data(ops);
> +	struct io_pgtable_cfg *cfg = &data->iop.cfg;
> +	dart_iopte *ptep = data->pgd;
> +	int ret, lvl = data->start_level;
> +	dart_iopte prot;
> +	long iaext = (s64)iova >> cfg->ias;

Do you have a split address space?

> +	if (WARN_ON(!pgsize || (pgsize & cfg->pgsize_bitmap) != pgsize))

Or effectively, "pgsize != cfg->pgsize_bitmap".

> +		return -EINVAL;
> +
> +	if (WARN_ON(iaext || paddr >> cfg->oas))
> +		return -ERANGE;
> +
> +	/* If no access, then nothing to do */
> +	if (!(iommu_prot & (IOMMU_READ | IOMMU_WRITE)))
> +		return 0;
> +
> +	prot = dart_prot_to_pte(data, iommu_prot);
> +	ret = __dart_map(data, iova, paddr, pgsize, pgcount, prot, lvl,
> +			     ptep, gfp, mapped);
> +	/*
> +	 * Synchronise all PTE updates for the new mapping before there's
> +	 * a chance for anything to kick off a table walk for the new iova.
> +	 */
> +	wmb();
> +
> +	return ret;
> +}
> +
> +static int dart_map(struct io_pgtable_ops *ops, unsigned long iova,
> +			phys_addr_t paddr, size_t size, int iommu_prot, gfp_t gfp)
> +{
> +	return dart_map_pages(ops, iova, paddr, size, 1, iommu_prot, gfp,
> +				  NULL);
> +}

There's no user for these wrappers, surely?

> +static void __dart_free_pgtable(struct dart_io_pgtable *data, int lvl,
> +				    dart_iopte *ptep)
> +{
> +	dart_iopte *start, *end;
> +	unsigned long table_size;
> +
> +	if (lvl == data->start_level)
> +		table_size = DART_PGD_SIZE(data);
> +	else
> +		table_size = DART_GRANULE(data);
> +
> +	start = ptep;
> +
> +	/* Only leaf entries at the last level */
> +	if (lvl == DART_MAX_LEVELS - 1)
> +		end = ptep;
> +	else
> +		end = (void *)ptep + table_size;
> +
> +	while (ptep != end) {
> +		dart_iopte pte = *ptep++;
> +
> +		if (!pte || iopte_leaf(pte, lvl, data->iop.fmt))
> +			continue;
> +
> +		__dart_free_pgtable(data, lvl + 1, iopte_deref(pte, data));
> +	}
> +
> +	__dart_free_pages(start, table_size);
> +}
> +
> +static size_t __dart_unmap(struct dart_io_pgtable *data,
> +			       struct iommu_iotlb_gather *gather,
> +			       unsigned long iova, size_t size, size_t pgcount,
> +			       int lvl, dart_iopte *ptep)
> +{
> +	dart_iopte pte;
> +	struct io_pgtable *iop = &data->iop;
> +	int i = 0, num_entries, max_entries, unmap_idx_start;
> +
> +	/* Something went horribly wrong and we ran out of page table */
> +	if (WARN_ON(lvl == DART_MAX_LEVELS))
> +		return 0;
> +
> +	unmap_idx_start = DART_LVL_IDX(iova, lvl, data);
> +	ptep += unmap_idx_start;
> +	pte = READ_ONCE(*ptep);
> +	if (WARN_ON(!pte))
> +		return 0;
> +
> +	/* If the size matches this level, we're in the right place */
> +	if (size == DART_BLOCK_SIZE(lvl, data)) {
> +		max_entries = DART_PTES_PER_TABLE(data) - unmap_idx_start;
> +		num_entries = min_t(int, pgcount, max_entries);
> +
> +		while (i < num_entries) {
> +			pte = READ_ONCE(*ptep);
> +			if (WARN_ON(!pte))
> +				break;
> +
> +			/* clear pte */
> +			*ptep = 0;
> +
> +			if (!iopte_leaf(pte, lvl, iop->fmt)) {

Again, this can't ever happen, and being non-recursive would let you see 
the wood for the trees. I suppose you could in principle still optimise 
for the case of "pgcount == DART_PTES_PER_TABLE" with a slightly 
different code structure, but I highly doubt it's worth the bother.

> +				/* Also flush any partial walks */
> +				io_pgtable_tlb_flush_walk(iop, iova + i * size, size,
> +							  DART_GRANULE(data));
> +				__dart_free_pgtable(data, lvl + 1, iopte_deref(pte, data));
> +			} else if (!iommu_iotlb_gather_queued(gather)) {
> +				io_pgtable_tlb_add_page(iop, gather, iova + i * size, size);
> +			}
> +
> +			ptep++;
> +			i++;
> +		}
> +
> +		return i * size;
> +	}
> +
> +	/* Keep on walkin' */
> +	ptep = iopte_deref(pte, data);
> +	return __dart_unmap(data, gather, iova, size, pgcount, lvl + 1, ptep);
> +}
> +
> +static size_t dart_unmap_pages(struct io_pgtable_ops *ops, unsigned long iova,
> +				   size_t pgsize, size_t pgcount,
> +				   struct iommu_iotlb_gather *gather)
> +{
> +	struct dart_io_pgtable *data = io_pgtable_ops_to_data(ops);
> +	struct io_pgtable_cfg *cfg = &data->iop.cfg;
> +	dart_iopte *ptep = data->pgd;
> +	long iaext = (s64)iova >> cfg->ias;
> +
> +	if (WARN_ON(!pgsize || (pgsize & cfg->pgsize_bitmap) != pgsize || !pgcount))
> +		return 0;
> +
> +	if (WARN_ON(iaext))
> +		return 0;
> +
> +	return __dart_unmap(data, gather, iova, pgsize, pgcount,
> +				data->start_level, ptep);
> +}
> +
> +static size_t dart_unmap(struct io_pgtable_ops *ops, unsigned long iova,
> +			     size_t size, struct iommu_iotlb_gather *gather)
> +{
> +	return dart_unmap_pages(ops, iova, size, 1, gather);
> +}
> +
> +static phys_addr_t dart_iova_to_phys(struct io_pgtable_ops *ops,
> +					 unsigned long iova)
> +{
> +	struct dart_io_pgtable *data = io_pgtable_ops_to_data(ops);
> +	dart_iopte pte, *ptep = data->pgd;
> +	int lvl = data->start_level;
> +
> +	do {
> +		/* Valid IOPTE pointer? */
> +		if (!ptep)
> +			return 0;
> +
> +		/* Grab the IOPTE we're interested in */
> +		ptep += DART_LVL_IDX(iova, lvl, data);
> +		pte = READ_ONCE(*ptep);
> +
> +		/* Valid entry? */
> +		if (!pte)
> +			return 0;
> +
> +		/* Leaf entry? */
> +		if (iopte_leaf(pte, lvl, data->iop.fmt))
> +			goto found_translation;
> +
> +		/* Take it to the next level */
> +		ptep = iopte_deref(pte, data);
> +	} while (++lvl < DART_MAX_LEVELS);

I imagine the compiler can unroll this loop already, but once again I'd 
argue that it's probably more readable to spell out the pgd and table 
lookups directly. When you have a fixed number of levels to walk, and 
know that you'll never find a valid translation before the last one, 
life is *so* much easier.

> +
> +	/* Ran out of page tables to walk */
> +	return 0;
> +
> +found_translation:
> +	iova &= (DART_BLOCK_SIZE(lvl, data) - 1);
> +	return iopte_to_paddr(pte, data) | iova;
> +}
> +
> +static void dart_restrict_pgsizes(struct io_pgtable_cfg *cfg)
> +{
> +	unsigned long granule, page_sizes;
> +	unsigned int max_addr_bits = 48;
> +
> +	/*
> +	 * We need to restrict the supported page sizes to match the
> +	 * translation regime for a particular granule. Aim to match
> +	 * the CPU page size if possible, otherwise prefer smaller sizes.
> +	 * While we're at it, restrict the block sizes to match the
> +	 * chosen granule.
> +	 */
> +	if (cfg->pgsize_bitmap & PAGE_SIZE)
> +		granule = PAGE_SIZE;
> +	else if (cfg->pgsize_bitmap & ~PAGE_MASK)
> +		granule = 1UL << __fls(cfg->pgsize_bitmap & ~PAGE_MASK);
> +	else if (cfg->pgsize_bitmap & PAGE_MASK)
> +		granule = 1UL << __ffs(cfg->pgsize_bitmap & PAGE_MASK);
> +	else
> +		granule = 0;
> +
> +	switch (granule) {
> +	case SZ_4K:
> +		page_sizes = (SZ_4K | SZ_2M | SZ_1G);
> +		break;
> +	case SZ_16K:
> +		page_sizes = (SZ_16K | SZ_32M);
> +		break;
> +	default:
> +		page_sizes = 0;
> +	}
> +
> +	cfg->pgsize_bitmap &= page_sizes;
> +	cfg->ias = min(cfg->ias, max_addr_bits);
> +	cfg->oas = min(cfg->oas, max_addr_bits);

Why is any of this here?

> +}
> +
> +static struct dart_io_pgtable *
> +dart_alloc_pgtable(struct io_pgtable_cfg *cfg)
> +{
> +	struct dart_io_pgtable *data;
> +	int bits_per_level, levels, va_bits, pg_shift;
> +
> +	dart_restrict_pgsizes(cfg);
> +
> +	if (!(cfg->pgsize_bitmap & (SZ_4K | SZ_16K)))
> +		return NULL;
> +
> +	if (cfg->ias > DART_MAX_ADDR_BITS)
> +		return NULL;
> +
> +	if (cfg->oas > DART_MAX_ADDR_BITS)
> +		return NULL;

You already checked this in the caller below.

> +	pg_shift = __ffs(cfg->pgsize_bitmap);
> +	bits_per_level = pg_shift - ilog2(sizeof(dart_iopte));
> +
> +	va_bits = cfg->ias - pg_shift;
> +	levels = DIV_ROUND_UP(va_bits, bits_per_level);
> +	if (levels > DART_MAX_LEVELS)
> +		return NULL;
> +
> +	data = kmalloc(sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return NULL;
> +
> +	data->bits_per_level = bits_per_level;
> +	data->start_level = DART_MAX_LEVELS - levels;
> +
> +	/* Calculate the actual size of our pgd (without concatenation) */
> +	data->pgd_bits = va_bits - (data->bits_per_level * (levels - 1));
> +
> +	data->iop.ops = (struct io_pgtable_ops) {
> +		.map		= dart_map,
> +		.map_pages	= dart_map_pages,
> +		.unmap		= dart_unmap,
> +		.unmap_pages	= dart_unmap_pages,
> +		.iova_to_phys	= dart_iova_to_phys,
> +	};
> +
> +	return data;
> +}
> +
> +static struct io_pgtable *
> +apple_dart_alloc_pgtable(struct io_pgtable_cfg *cfg, void *cookie)
> +{
> +	struct dart_io_pgtable *data;
> +	int i;
> +
> +	if (!cfg->coherent_walk)
> +		return NULL;
> +
> +	if (cfg->oas > 36)
> +		return NULL;
> +
> +	data = dart_alloc_pgtable(cfg);
> +	if (!data)
> +		return NULL;
> +
> +	/*
> +	 * The table format itself always uses two levels, but the total VA
> +	 * space is mapped by four separate tables, making the MMIO registers
> +	 * an effective "level 1". For simplicity, though, we treat this
> +	 * equivalently to LPAE stage 2 concatenation at level 2, with the
> +	 * additional TTBRs each just pointing at consecutive pages.
> +	 */
> +	if (data->start_level == 0 && data->pgd_bits > 2)
> +		goto out_free_data;
> +	if (data->start_level > 0)
> +		data->pgd_bits = 0;
> +	data->start_level = 1;
> +	cfg->apple_dart_cfg.n_ttbrs = 1 << data->pgd_bits;
> +	data->pgd_bits += data->bits_per_level;
> +
> +	data->pgd = __dart_alloc_pages(DART_PGD_SIZE(data), GFP_KERNEL,
> +					   cfg);
> +	if (!data->pgd)
> +		goto out_free_data;

If recursive map/unmap goes away then you'll also be free to drop the 
forced concatenation and allocate pgds individually, which should then 
have further knock-on simplification effects elsewhere, primarily 
__dart_free_pgtable() I think.

Still, for the split from io-pgtable-arm, and with the Kconfig fixed,

Acked-by: Robin Murphy <rpbin.murphy@....com>

Cheers,
Robin.

> +
> +	for (i = 0; i < cfg->apple_dart_cfg.n_ttbrs; ++i)
> +		cfg->apple_dart_cfg.ttbr[i] =
> +			virt_to_phys(data->pgd + i * DART_GRANULE(data));
> +
> +	return &data->iop;
> +
> +out_free_data:
> +	kfree(data);
> +	return NULL;
> +}
> +
> +static void apple_dart_free_pgtable(struct io_pgtable *iop)
> +{
> +	struct dart_io_pgtable *data = io_pgtable_to_data(iop);
> +
> +	__dart_free_pgtable(data, data->start_level, data->pgd);
> +	kfree(data);
> +}
> +
> +struct io_pgtable_init_fns io_pgtable_apple_dart_init_fns = {
> +	.alloc	= apple_dart_alloc_pgtable,
> +	.free	= apple_dart_free_pgtable,
> +};
> diff --git a/drivers/iommu/io-pgtable.c b/drivers/iommu/io-pgtable.c
> index f4bfcef98297..e6edc6686859 100644
> --- a/drivers/iommu/io-pgtable.c
> +++ b/drivers/iommu/io-pgtable.c
> @@ -20,6 +20,8 @@ io_pgtable_init_table[IO_PGTABLE_NUM_FMTS] = {
>   	[ARM_64_LPAE_S1] = &io_pgtable_arm_64_lpae_s1_init_fns,
>   	[ARM_64_LPAE_S2] = &io_pgtable_arm_64_lpae_s2_init_fns,
>   	[ARM_MALI_LPAE] = &io_pgtable_arm_mali_lpae_init_fns,
> +#endif
> +#ifdef CONFIG_APPLE_DART
>   	[APPLE_DART] = &io_pgtable_apple_dart_init_fns,
>   #endif
>   #ifdef CONFIG_IOMMU_IO_PGTABLE_ARMV7S

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