iommu: io-pgtable: Add locked DART quirk

Apple DARTs can be locked by the bootloader. In particular, we cannot
change the TTBR address for these DARTs. However, we may take over the
existing allocated page. We clear the existing page table. Important
mappings will be restored by reserved regions.
Add a quirk for this case and handle it.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Co-developed-by: Janne Grunau <j@jannau.net>
Signed-off-by: Janne Grunau <j@jannau.net>

Author: alyssarosenzweig

drivers/iommu/apple-dart.c

@@ -596,6 +596,29 @@ static int apple_dart_finalize_domain(struct iommu_domain *domain,
 		.iommu_dev = dart->dev,
 	};
 
+	if (dart->locked) {
+		unsigned long *sidmap;
+		int sid;
+		phys_addr_t phys;
+		u32 ttbr;
+
+		/* Locked DARTs can only have a single stream bound */
+		sidmap = cfg->stream_maps[0].sidmap;
+		sid = find_first_bit(sidmap, dart->num_streams);
+
+		WARN_ON((sid < 0) || bitmap_weight(sidmap, dart->num_streams) > 1);
+		ttbr = readl(dart->regs + DART_TTBR(dart, sid, 0));
+
+		WARN_ON(!(ttbr & dart->hw->ttbr_valid));
+		ttbr &= ~dart->hw->ttbr_valid;
+		if (dart->hw->ttbr_addr_field_shift)
+			ttbr >>= dart->hw->ttbr_addr_field_shift;
+
+		phys = ((phys_addr_t) ttbr) << dart->hw->ttbr_shift;
+		pgtbl_cfg.apple_dart_cfg.ttbr[0] = phys;
+		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_APPLE_LOCKED;
+	}
+
 	dart_domain->pgtbl_ops =
 		alloc_io_pgtable_ops(dart->hw->fmt, &pgtbl_cfg, domain);
 	if (!dart_domain->pgtbl_ops) {

drivers/iommu/io-pgtable-dart.c

@@ -16,6 +16,7 @@
 #include <linux/atomic.h>
 #include <linux/bitfield.h>
 #include <linux/bitops.h>
+#include <linux/io.h>
 #include <linux/io-pgtable.h>
 #include <linux/kernel.h>
 #include <linux/sizes.h>
@@ -417,29 +418,55 @@ apple_dart_alloc_pgtable(struct io_pgtable_cfg *cfg, void *cookie)
 
 	cfg->apple_dart_cfg.n_ttbrs = 1 << data->tbl_bits;
 
+	/* Locked DARTs can not modify the TTBR registers. The known locked
+	 * DARTs (dcp, dcpext0) use just a single TTBR so we do not have to
+	 * worry whether the pages are consecutive.
+	 */
+	if (cfg->quirks & IO_PGTABLE_QUIRK_APPLE_LOCKED) {
+		size_t size = cfg->pgsize_bitmap;
+		if (cfg->apple_dart_cfg.n_ttbrs > 1)
+			goto out_free_data;
+
+		data->pgd[0] = devm_memremap(cfg->iommu_dev,
+					     cfg->apple_dart_cfg.ttbr[0],
+					     size, MEMREMAP_WB);
+		if (!data->pgd[0])
+			goto out_free_data;
+		/* start with an empty table */
+		memset(data->pgd[0], 0, size);
+		return &data->iop;
+	}
+
 	for (i = 0; i < cfg->apple_dart_cfg.n_ttbrs; ++i) {
 		data->pgd[i] = __dart_alloc_pages(DART_GRANULE(data), GFP_KERNEL);
 		if (!data->pgd[i])
-			goto out_free_data;
+			goto out_free_pages;
 		cfg->apple_dart_cfg.ttbr[i] = virt_to_phys(data->pgd[i]);
 	}
 
 	return &data->iop;
 
-out_free_data:
+out_free_pages:
 	while (--i >= 0)
 		free_pages((unsigned long)data->pgd[i],
 			   get_order(DART_GRANULE(data)));
+out_free_data:
 	kfree(data);
 	return NULL;
 }
 
 static void apple_dart_free_pgtable(struct io_pgtable *iop)
 {
+	struct io_pgtable_cfg *cfg = &iop->cfg;
 	struct dart_io_pgtable *data = io_pgtable_to_data(iop);
 	dart_iopte *ptep, *end;
 	int i;
 
+        if (cfg->quirks & IO_PGTABLE_QUIRK_APPLE_LOCKED) {
+		kfree(data);
+		return;
+	}
+
 	for (i = 0; i < (1 << data->tbl_bits) && data->pgd[i]; ++i) {
 		ptep = data->pgd[i];
 		end = (void *)ptep + DART_GRANULE(data);

include/linux/io-pgtable.h

@@ -85,13 +85,17 @@ struct io_pgtable_cfg {
 	 *
 	 * IO_PGTABLE_QUIRK_ARM_OUTER_WBWA: Override the outer-cacheability
 	 *	attributes set in the TCR for a non-coherent page-table walker.
+	 *
+	 * IO_PGTABLE_QUIRK_APPLE_LOCKED: Cannot modify the TTBR pointer, must
+	 *	inherit mappings from the bootloader.
 	 */
 	#define IO_PGTABLE_QUIRK_ARM_NS			BIT(0)
 	#define IO_PGTABLE_QUIRK_NO_PERMS		BIT(1)
 	#define IO_PGTABLE_QUIRK_ARM_MTK_EXT		BIT(3)
 	#define IO_PGTABLE_QUIRK_ARM_MTK_TTBR_EXT	BIT(4)
 	#define IO_PGTABLE_QUIRK_ARM_TTBR1		BIT(5)
 	#define IO_PGTABLE_QUIRK_ARM_OUTER_WBWA		BIT(6)
+	#define IO_PGTABLE_QUIRK_APPLE_LOCKED		BIT(7)
 	unsigned long			quirks;
 	unsigned long			pgsize_bitmap;
 	unsigned int			ias;