iommu/io-pgtable: Rationalise quirk handling

As the number of io-pgtable implementations grows beyond 1, it's time
to rationalise the quirks mechanism before things have a chance to
start getting really ugly and out-of-hand.

To that end:
- Indicate exactly which quirks each format can/does support.
- Fail creating a table if a caller wants unsupported quirks.
- Properly document where each quirk applies and why.
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

drivers/iommu/io-pgtable-arm-v7s.c

@@ -623,6 +623,11 @@ static struct io_pgtable *arm_v7s_alloc_pgtable(struct io_pgtable_cfg *cfg,
 	if (cfg->ias > ARM_V7S_ADDR_BITS || cfg->oas > ARM_V7S_ADDR_BITS)
 		return NULL;
 
+	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS |
+			    IO_PGTABLE_QUIRK_NO_PERMS |
+			    IO_PGTABLE_QUIRK_TLBI_ON_MAP))
+		return NULL;
+
 	data = kmalloc(sizeof(*data), GFP_KERNEL);
 	if (!data)
 		return NULL;

drivers/iommu/io-pgtable-arm.c

@@ -659,8 +659,12 @@ static struct io_pgtable *
 arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie)
 {
 	u64 reg;
-	struct arm_lpae_io_pgtable *data = arm_lpae_alloc_pgtable(cfg);
+	struct arm_lpae_io_pgtable *data;
+
+	if (cfg->quirks & ~IO_PGTABLE_QUIRK_ARM_NS)
+		return NULL;
 
+	data = arm_lpae_alloc_pgtable(cfg);
 	if (!data)
 		return NULL;
 
@@ -743,8 +747,13 @@ static struct io_pgtable *
 arm_64_lpae_alloc_pgtable_s2(struct io_pgtable_cfg *cfg, void *cookie)
 {
 	u64 reg, sl;
-	struct arm_lpae_io_pgtable *data = arm_lpae_alloc_pgtable(cfg);
+	struct arm_lpae_io_pgtable *data;
+
+	/* The NS quirk doesn't apply at stage 2 */
+	if (cfg->quirks)
+		return NULL;
 
+	data = arm_lpae_alloc_pgtable(cfg);
 	if (!data)
 		return NULL;
 

drivers/iommu/io-pgtable.h

@@ -47,10 +47,24 @@ struct iommu_gather_ops {
  *                 page table walker.
  */
 struct io_pgtable_cfg {
-	#define IO_PGTABLE_QUIRK_ARM_NS		BIT(0) /* Set NS bit in PTEs */
-	#define IO_PGTABLE_QUIRK_NO_PERMS	BIT(1) /* No AP/XN bits */
-	#define IO_PGTABLE_QUIRK_TLBI_ON_MAP	BIT(2) /* TLB Inv. on map */
-	int				quirks;
+	/*
+	 * IO_PGTABLE_QUIRK_ARM_NS: (ARM formats) Set NS and NSTABLE bits in
+	 *	stage 1 PTEs, for hardware which insists on validating them
+	 *	even in	non-secure state where they should normally be ignored.
+	 *
+	 * IO_PGTABLE_QUIRK_NO_PERMS: Ignore the IOMMU_READ, IOMMU_WRITE and
+	 *	IOMMU_NOEXEC flags and map everything with full access, for
+	 *	hardware which does not implement the permissions of a given
+	 *	format, and/or requires some format-specific default value.
+	 *
+	 * IO_PGTABLE_QUIRK_TLBI_ON_MAP: If the format forbids caching invalid
+	 *	(unmapped) entries but the hardware might do so anyway, perform
+	 *	TLB maintenance when mapping as well as when unmapping.
+	 */
+	#define IO_PGTABLE_QUIRK_ARM_NS		BIT(0)
+	#define IO_PGTABLE_QUIRK_NO_PERMS	BIT(1)
+	#define IO_PGTABLE_QUIRK_TLBI_ON_MAP	BIT(2)
+	unsigned long			quirks;
 	unsigned long			pgsize_bitmap;
 	unsigned int			ias;
 	unsigned int			oas;