iommu: Add IOMMU uclass

This uclass is intended to manage IOMMUs on systems where the
IOMMUs are not in bypass mode by default.  In that case U-Boot
cannot ignore the IOMMUs if it wants to use devices that need
to do DMA and sit behind such an IOMMU.

This initial IOMMU uclass implementation does not implement and
device ops and is intended for IOMMUs that have a bypass mode
that does not require address translation.  Support for IOMMUs
that do require address translation is planned and device ops
will be defined when support for such IOMMUs will be added.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Simon Glass <sjg@chromium.org>

drivers/Kconfig

@@ -50,6 +50,8 @@ source "drivers/i2c/Kconfig"
 
 source "drivers/input/Kconfig"
 
+source "drivers/iommu/Kconfig"
+
 source "drivers/led/Kconfig"
 
 source "drivers/mailbox/Kconfig"

drivers/Makefile

@@ -102,6 +102,7 @@ obj-y += mtd/
 obj-y += pwm/
 obj-y += reset/
 obj-y += input/
+obj-y += iommu/
 # SOC specific infrastructure drivers.
 obj-y += smem/
 obj-y += thermal/

drivers/core/device.c

@@ -28,6 +28,7 @@
 #include <dm/uclass.h>
 #include <dm/uclass-internal.h>
 #include <dm/util.h>
+#include <iommu.h>
 #include <linux/err.h>
 #include <linux/list.h>
 #include <power-domain.h>
@@ -543,6 +544,13 @@ int device_probe(struct udevice *dev)
 			goto fail;
 	}
 
+	if (CONFIG_IS_ENABLED(IOMMU) && dev->parent &&
+	    (device_get_uclass_id(dev) != UCLASS_IOMMU)) {
+		ret = dev_iommu_enable(dev);
+		if (ret)
+			goto fail;
+	}
+
 	ret = device_get_dma_constraints(dev);
 	if (ret)
 		goto fail;

drivers/iommu/Kconfig

@@ -0,0 +1,17 @@
+#
+# IOMMU devices
+#
+
+menu "IOMMU device drivers"
+
+config IOMMU
+	bool "Enable Driver Model for IOMMU drivers"
+	depends on DM
+	help
+	  Enable driver model for IOMMU devices. An IOMMU maps device
+	  virtiual memory addresses to physical addresses. Devices
+	  that sit behind an IOMMU can typically only access physical
+	  memory if the IOMMU has been programmed to allow access to
+	  that memory.
+
+endmenu

drivers/iommu/Makefile

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0+
+
+obj-$(CONFIG_IOMMU) += iommu-uclass.o

drivers/iommu/iommu-uclass.c

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2021 Mark Kettenis <kettenis@openbsd.org>
+ */
+
+#define LOG_CATEGORY UCLASS_IOMMU
+
+#include <common.h>
+#include <dm.h>
+
+#if (CONFIG_IS_ENABLED(OF_CONTROL) && !CONFIG_IS_ENABLED(OF_PLATDATA))
+int dev_iommu_enable(struct udevice *dev)
+{
+	struct ofnode_phandle_args args;
+	struct udevice *dev_iommu;
+	int i, count, ret = 0;
+
+	count = dev_count_phandle_with_args(dev, "iommus",
+					    "#iommu-cells", 0);
+	for (i = 0; i < count; i++) {
+		ret = dev_read_phandle_with_args(dev, "iommus",
+						 "#iommu-cells", 0, i, &args);
+		if (ret) {
+			debug("%s: dev_read_phandle_with_args failed: %d\n",
+			      __func__, ret);
+			return ret;
+		}
+
+		ret = uclass_get_device_by_ofnode(UCLASS_IOMMU, args.node,
+						  &dev_iommu);
+		if (ret) {
+			debug("%s: uclass_get_device_by_ofnode failed: %d\n",
+			      __func__, ret);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+#endif
+
+UCLASS_DRIVER(iommu) = {
+	.id		= UCLASS_IOMMU,
+	.name		= "iommu",
+};