soc: apple: Add SART driver

The NVMe co-processor on the Apple M1 uses a DMA address filter called
SART for some DMA transactions. This adds a simple driver used to
configure the memory regions from which DMA transactions are allowed.

Unlike a real IOMMU, SART does not support any pagetables and can't be
implemented inside the IOMMU subsystem using iommu_ops.

It also can't be implemented using dma_map_ops since not all DMA
transactions of the NVMe controller are filtered by SART.
Instead, most buffers have to be registered using the integrated NVMe
IOMMU and we can't have two separate dma_map_ops implementations for a
single device.

Co-developed-by: Hector Martin <marcan@marcan.st>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Sven Peter <sven@svenpeter.dev>

MAINTAINERS

@@ -1854,6 +1854,7 @@ F:	drivers/watchdog/apple_wdt.c
 F:	include/dt-bindings/interrupt-controller/apple-aic.h
 F:	include/dt-bindings/pinctrl/apple.h
 F:	include/linux/apple-mailbox.h
+F:	include/linux/soc/apple/*
 
 ARM/ARTPEC MACHINE SUPPORT
 M:	Jesper Nilsson <jesper.nilsson@axis.com>

drivers/soc/apple/Kconfig

@@ -30,6 +30,17 @@ config APPLE_RTKIT
 
 	  Say 'y' here if you have an Apple SoC.
 
+config APPLE_SART
+	tristate "Apple SART DMA address filter"
+	depends on ARCH_APPLE || COMPILE_TEST
+	default ARCH_APPLE
+	help
+	  Apple SART is a simple DMA address filter used on Apple SoCs such
+	  as the M1. It is usually required for the NVMe coprocessor which does
+	  not use a proper IOMMU.
+
+	  Say 'y' here if you have an Apple SoC.
+
 endmenu
 
 endif

drivers/soc/apple/Makefile

@@ -3,3 +3,6 @@ obj-$(CONFIG_APPLE_PMGR_PWRSTATE)	+= apple-pmgr-pwrstate.o
 
 obj-$(CONFIG_APPLE_RTKIT) += apple-rtkit.o
 apple-rtkit-y = rtkit.o rtkit-crashlog.o
+
+obj-$(CONFIG_APPLE_SART) += apple-sart.o
+apple-sart-y = sart.o

drivers/soc/apple/sart.c

@@ -0,0 +1,328 @@
+// SPDX-License-Identifier: GPL-2.0-only OR MIT
+/*
+ * Apple SART device driver
+ * Copyright (C) The Asahi Linux Contributors
+ *
+ * Apple SART is a simple address filter for some DMA transactions.
+ * Regions of physical memory must be added to the SART's allow
+ * list before any DMA can target these. Unlike a proper
+ * IOMMU no remapping can be done and special support in the
+ * consumer driver is required since not all DMA transactions of
+ * a single device are subject to SART filtering.
+ */
+
+#include <linux/soc/apple/sart.h>
+#include <linux/atomic.h>
+#include <linux/bits.h>
+#include <linux/bitfield.h>
+#include <linux/device.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/types.h>
+
+#define APPLE_SART_MAX_ENTRIES 16
+
+/* This is probably a bitfield but the exact meaning of each bit is unknown. */
+#define APPLE_SART_FLAGS_ALLOW 0xff
+
+/* SARTv2 registers */
+#define APPLE_SART2_CONFIG(idx)	      (0x00 + 4 * (idx))
+#define APPLE_SART2_CONFIG_FLAGS      GENMASK(31, 24)
+#define APPLE_SART2_CONFIG_SIZE	      GENMASK(23, 0)
+#define APPLE_SART2_CONFIG_SIZE_SHIFT 12
+#define APPLE_SART2_CONFIG_SIZE_MAX   GENMASK(23, 0)
+
+#define APPLE_SART2_PADDR(idx)	(0x40 + 4 * (idx))
+#define APPLE_SART2_PADDR_SHIFT 12
+
+/* SARTv3 registers */
+#define APPLE_SART3_CONFIG(idx) (0x00 + 4 * (idx))
+
+#define APPLE_SART3_PADDR(idx)	(0x40 + 4 * (idx))
+#define APPLE_SART3_PADDR_SHIFT 12
+
+#define APPLE_SART3_SIZE(idx)  (0x80 + 4 * (idx))
+#define APPLE_SART3_SIZE_SHIFT 12
+#define APPLE_SART3_SIZE_MAX   GENMASK(29, 0)
+
+struct apple_sart_ops {
+	void (*get_entry)(struct apple_sart *sart, int index, u8 *flags,
+			  phys_addr_t *paddr, size_t *size);
+	void (*set_entry)(struct apple_sart *sart, int index, u8 flags,
+			  phys_addr_t paddr_shifted, size_t size_shifted);
+	unsigned int size_shift;
+	unsigned int paddr_shift;
+	size_t size_max;
+};
+
+struct apple_sart {
+	struct device *dev;
+	void __iomem *regs;
+
+	const struct apple_sart_ops *ops;
+
+	unsigned long protected_entries;
+	unsigned long used_entries;
+};
+
+static void sart2_get_entry(struct apple_sart *sart, int index, u8 *flags,
+			    phys_addr_t *paddr, size_t *size)
+{
+	u32 cfg = readl(sart->regs + APPLE_SART2_CONFIG(index));
+	phys_addr_t paddr_ = readl(sart->regs + APPLE_SART2_PADDR(index));
+	size_t size_ = FIELD_GET(APPLE_SART2_CONFIG_SIZE, cfg);
+
+	*flags = FIELD_GET(APPLE_SART2_CONFIG_FLAGS, cfg);
+	*size = size_ << APPLE_SART2_CONFIG_SIZE_SHIFT;
+	*paddr = paddr_ << APPLE_SART2_PADDR_SHIFT;
+}
+
+static void sart2_set_entry(struct apple_sart *sart, int index, u8 flags,
+			    phys_addr_t paddr_shifted, size_t size_shifted)
+{
+	u32 cfg;
+
+	cfg = FIELD_PREP(APPLE_SART2_CONFIG_FLAGS, flags);
+	cfg |= FIELD_PREP(APPLE_SART2_CONFIG_SIZE, size_shifted);
+
+	writel(paddr_shifted, sart->regs + APPLE_SART2_PADDR(index));
+	writel(cfg, sart->regs + APPLE_SART2_CONFIG(index));
+}
+
+static struct apple_sart_ops sart_ops_v2 = {
+	.get_entry = sart2_get_entry,
+	.set_entry = sart2_set_entry,
+	.size_shift = APPLE_SART2_CONFIG_SIZE_SHIFT,
+	.paddr_shift = APPLE_SART2_PADDR_SHIFT,
+	.size_max = APPLE_SART2_CONFIG_SIZE_MAX,
+};
+
+static void sart3_get_entry(struct apple_sart *sart, int index, u8 *flags,
+			    phys_addr_t *paddr, size_t *size)
+{
+	phys_addr_t paddr_ = readl(sart->regs + APPLE_SART3_PADDR(index));
+	size_t size_ = readl(sart->regs + APPLE_SART3_SIZE(index));
+
+	*flags = readl(sart->regs + APPLE_SART3_CONFIG(index));
+	*size = size_ << APPLE_SART3_SIZE_SHIFT;
+	*paddr = paddr_ << APPLE_SART3_PADDR_SHIFT;
+}
+
+static void sart3_set_entry(struct apple_sart *sart, int index, u8 flags,
+			    phys_addr_t paddr_shifted, size_t size_shifted)
+{
+	writel(paddr_shifted, sart->regs + APPLE_SART3_PADDR(index));
+	writel(size_shifted, sart->regs + APPLE_SART3_SIZE(index));
+	writel(flags, sart->regs + APPLE_SART3_CONFIG(index));
+}
+
+static struct apple_sart_ops sart_ops_v3 = {
+	.get_entry = sart3_get_entry,
+	.set_entry = sart3_set_entry,
+	.size_shift = APPLE_SART3_SIZE_SHIFT,
+	.paddr_shift = APPLE_SART3_PADDR_SHIFT,
+	.size_max = APPLE_SART3_SIZE_MAX,
+};
+
+static int apple_sart_probe(struct platform_device *pdev)
+{
+	int i;
+	struct apple_sart *sart;
+	struct device *dev = &pdev->dev;
+
+	sart = devm_kzalloc(dev, sizeof(*sart), GFP_KERNEL);
+	if (!sart)
+		return -ENOMEM;
+
+	sart->dev = dev;
+	sart->ops = of_device_get_match_data(dev);
+
+	sart->regs = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(sart->regs))
+		return PTR_ERR(sart->regs);
+
+	for (i = 0; i < APPLE_SART_MAX_ENTRIES; ++i) {
+		u8 flags;
+		size_t size;
+		phys_addr_t paddr;
+
+		sart->ops->get_entry(sart, i, &flags, &paddr, &size);
+
+		if (!flags)
+			continue;
+
+		dev_dbg(sart->dev,
+			"SART bootloader entry: index %02d; flags: 0x%02x; paddr: %pa; size: 0x%zx\n",
+			i, flags, &paddr, size);
+		set_bit(i, &sart->protected_entries);
+	}
+
+	platform_set_drvdata(pdev, sart);
+	return 0;
+}
+
+struct apple_sart *devm_apple_sart_get(struct device *dev)
+{
+	struct device_node *sart_node;
+	struct platform_device *sart_pdev;
+	struct apple_sart *sart;
+	int ret;
+
+	sart_node = of_parse_phandle(dev->of_node, "apple,sart", 0);
+	if (!sart_node)
+		return ERR_PTR(-ENODEV);
+
+	sart_pdev = of_find_device_by_node(sart_node);
+	of_node_put(sart_node);
+
+	if (!sart_pdev)
+		return ERR_PTR(-ENODEV);
+
+	sart = dev_get_drvdata(&sart_pdev->dev);
+	if (!sart) {
+		put_device(&sart_pdev->dev);
+		return ERR_PTR(-EPROBE_DEFER);
+	}
+
+	ret = devm_add_action_or_reset(dev, (void (*)(void *))put_device,
+				       &sart_pdev->dev);
+	if (ret)
+		return ERR_PTR(ret);
+
+	device_link_add(dev, &sart_pdev->dev,
+			DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_SUPPLIER);
+
+	return sart;
+}
+EXPORT_SYMBOL_GPL(devm_apple_sart_get);
+
+static int sart_set_entry(struct apple_sart *sart, int index, u8 flags,
+			  phys_addr_t paddr, size_t size)
+{
+	if (size & ((1 << sart->ops->size_shift) - 1))
+		return -EINVAL;
+	if (paddr & ((1 << sart->ops->paddr_shift) - 1))
+		return -EINVAL;
+
+	paddr >>= sart->ops->size_shift;
+	size >>= sart->ops->paddr_shift;
+
+	if (size > sart->ops->size_max)
+		return -EINVAL;
+
+	sart->ops->set_entry(sart, index, flags, paddr, size);
+	return 0;
+}
+
+int apple_sart_add_allowed_region(struct apple_sart *sart, phys_addr_t paddr,
+				  size_t size)
+{
+	int i, ret;
+
+	for (i = 0; i < APPLE_SART_MAX_ENTRIES; ++i) {
+		if (test_bit(i, &sart->protected_entries))
+			continue;
+		if (test_and_set_bit(i, &sart->used_entries))
+			continue;
+
+		ret = sart_set_entry(sart, i, APPLE_SART_FLAGS_ALLOW, paddr,
+				     size);
+		if (ret) {
+			dev_dbg(sart->dev,
+				"unable to set entry %d to [%pa, 0x%zx]\n",
+				i, &paddr, size);
+			clear_bit(i, &sart->used_entries);
+			return ret;
+		}
+
+		dev_dbg(sart->dev, "wrote [%pa, 0x%zx] to %d\n", &paddr, size,
+			i);
+		return 0;
+	}
+
+	dev_warn(sart->dev,
+		 "no free entries left to add [paddr: 0x%pa, size: 0x%zx]\n",
+		 &paddr, size);
+
+	return -EBUSY;
+}
+EXPORT_SYMBOL_GPL(apple_sart_add_allowed_region);
+
+int apple_sart_remove_allowed_region(struct apple_sart *sart, phys_addr_t paddr,
+				     size_t size)
+{
+	int i;
+
+	dev_dbg(sart->dev,
+		"will remove [paddr: %pa, size: 0x%zx] from allowed regions\n",
+		&paddr, size);
+
+	for (i = 0; i < APPLE_SART_MAX_ENTRIES; ++i) {
+		u8 eflags;
+		size_t esize;
+		phys_addr_t epaddr;
+
+		if (test_bit(i, &sart->protected_entries))
+			continue;
+
+		sart->ops->get_entry(sart, i, &eflags, &epaddr, &esize);
+
+		if (epaddr != paddr || esize != size)
+			continue;
+
+		sart->ops->set_entry(sart, i, 0, 0, 0);
+
+		clear_bit(i, &sart->used_entries);
+		dev_dbg(sart->dev, "cleared entry %d\n", i);
+		return 0;
+	}
+
+	dev_warn(sart->dev, "entry [paddr: 0x%llx, size: 0x%zx] not found\n",
+		 paddr, size);
+
+	return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(apple_sart_remove_allowed_region);
+
+static void apple_sart_shutdown(struct platform_device *pdev)
+{
+	struct apple_sart *sart = dev_get_drvdata(&pdev->dev);
+	int i;
+
+	for (i = 0; i < APPLE_SART_MAX_ENTRIES; ++i) {
+		if (test_bit(i, &sart->protected_entries))
+			continue;
+
+		sart->ops->set_entry(sart, i, 0, 0, 0);
+	}
+}
+
+static const struct of_device_id apple_sart_of_match[] = {
+	{
+		.compatible = "apple,t6000-sart",
+		.data = &sart_ops_v3,
+	},
+	{
+		.compatible = "apple,t8103-sart",
+		.data = &sart_ops_v2,
+	},
+	{}
+};
+MODULE_DEVICE_TABLE(of, apple_sart_of_match);
+
+static struct platform_driver apple_sart_driver = {
+	.driver = {
+		.name = "apple-sart",
+		.of_match_table = apple_sart_of_match,
+	},
+	.probe = apple_sart_probe,
+	.shutdown = apple_sart_shutdown,
+};
+module_platform_driver(apple_sart_driver);
+
+MODULE_LICENSE("Dual MIT/GPL");
+MODULE_AUTHOR("Sven Peter <sven@svenpeter.dev>");
+MODULE_DESCRIPTION("Apple SART driver");