diff --git a/drivers/gpu/nvgpu/common/io/io.c b/drivers/gpu/nvgpu/common/io/io.c
index e77771596..2f541c370 100644
--- a/drivers/gpu/nvgpu/common/io/io.c
+++ b/drivers/gpu/nvgpu/common/io/io.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2018-2021, NVIDIA CORPORATION.  All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -24,6 +24,114 @@
 #include <nvgpu/types.h>
 #include <nvgpu/bug.h>
 #include <nvgpu/gk20a.h>
+#include <nvgpu/nvgpu_init.h>
+
+static void nvgpu_warn_on_no_regs(struct gk20a *g)
+{
+	nvgpu_warn(g, "Attempted access to GPU regs after unmapping!");
+}
+
+void nvgpu_writel(struct gk20a *g, u32 r, u32 v)
+{
+	if (unlikely(!g->regs)) {
+		nvgpu_warn_on_no_regs(g);
+		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x (failed)", r, v);
+	} else {
+		nvgpu_os_writel(v, g->regs + r);
+		nvgpu_wmb();
+		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x", r, v);
+	}
+}
+
+#ifdef CONFIG_NVGPU_DGPU
+void nvgpu_writel_relaxed(struct gk20a *g, u32 r, u32 v)
+{
+	if (unlikely(!g->regs)) {
+		nvgpu_warn_on_no_regs(g);
+		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x (failed)", r, v);
+	} else {
+		nvgpu_os_writel_relaxed(v, g->regs + r);
+	}
+}
+#endif
+
+u32 nvgpu_readl(struct gk20a *g, u32 r)
+{
+	u32 v = nvgpu_readl_impl(g, r);
+
+	if (v == 0xffffffff)
+		nvgpu_check_gpu_state(g);
+
+	return v;
+}
+
+u32 nvgpu_readl_impl(struct gk20a *g, u32 r)
+{
+	u32 v = 0xffffffff;
+
+	if (unlikely(!g->regs)) {
+		nvgpu_warn_on_no_regs(g);
+		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x (failed)", r, v);
+	} else {
+		v = nvgpu_os_readl(g->regs + r);
+		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x", r, v);
+	}
+
+	return v;
+}
+
+#ifdef CONFIG_NVGPU_NON_FUSA
+void nvgpu_writel_loop(struct gk20a *g, u32 r, u32 v)
+{
+	if (unlikely(!g->regs)) {
+		nvgpu_warn_on_no_regs(g);
+		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x (failed)", r, v);
+	} else {
+		nvgpu_wmb();
+		do {
+			nvgpu_os_writel(v, g->regs + r);
+		} while (nvgpu_os_readl(g->regs + r) != v);
+		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x", r, v);
+	}
+}
+#endif
+
+void nvgpu_bar1_writel(struct gk20a *g, u32 b, u32 v)
+{
+	if (unlikely(!g->bar1)) {
+		nvgpu_warn_on_no_regs(g);
+		nvgpu_log(g, gpu_dbg_reg, "b=0x%x v=0x%x (failed)", b, v);
+	} else {
+		nvgpu_wmb();
+		nvgpu_os_writel(v, g->bar1 + b);
+		nvgpu_log(g, gpu_dbg_reg, "b=0x%x v=0x%x", b, v);
+	}
+}
+
+u32 nvgpu_bar1_readl(struct gk20a *g, u32 b)
+{
+	u32 v = 0xffffffff;
+
+	if (unlikely(!g->bar1)) {
+		nvgpu_warn_on_no_regs(g);
+		nvgpu_log(g, gpu_dbg_reg, "b=0x%x v=0x%x (failed)", b, v);
+	} else {
+		v = nvgpu_os_readl(g->bar1 + b);
+		nvgpu_log(g, gpu_dbg_reg, "b=0x%x v=0x%x", b, v);
+	}
+
+	return v;
+}
+
+bool nvgpu_io_exists(struct gk20a *g)
+{
+	return g->regs != 0U;
+}
+
+bool nvgpu_io_valid_reg(struct gk20a *g, u32 r)
+{
+	return r < g->regs_size;
+}
 
 void nvgpu_writel_check(struct gk20a *g, u32 r, u32 v)
 {
diff --git a/drivers/gpu/nvgpu/include/nvgpu/gk20a.h b/drivers/gpu/nvgpu/include/nvgpu/gk20a.h
index 6483dff50..489ae1c3f 100644
--- a/drivers/gpu/nvgpu/include/nvgpu/gk20a.h
+++ b/drivers/gpu/nvgpu/include/nvgpu/gk20a.h
@@ -336,6 +336,22 @@ struct gk20a {
 	 */
 	void (*gfree)(struct gk20a *g);
 
+	/** Starting virtual address of mapped bar0 io region. */
+	uintptr_t regs;
+	u64 regs_size;
+	u64 regs_bus_addr;
+
+	/** Starting virtual address of mapped bar1 io region. */
+	uintptr_t bar1;
+
+	/** Starting virtual address of usermode registers io region. */
+	uintptr_t usermode_regs;
+	u64 usermode_regs_bus_addr;
+
+	uintptr_t regs_saved;
+	uintptr_t bar1_saved;
+	uintptr_t usermode_regs_saved;
+
 	/**
 	 * Handle to access nvhost APIs.
 	 */
diff --git a/drivers/gpu/nvgpu/include/nvgpu/io.h b/drivers/gpu/nvgpu/include/nvgpu/io.h
index e9cda7e82..de53b825c 100644
--- a/drivers/gpu/nvgpu/include/nvgpu/io.h
+++ b/drivers/gpu/nvgpu/include/nvgpu/io.h
@@ -24,6 +24,44 @@
 
 #include <nvgpu/types.h>
 
+/**
+ * @brief Read a value from a register.
+ *
+ * @param addr [in]		Register cpu virtual address.
+ *
+ * Read a 32-bit value from the register cpu virtuall address.
+ * OS layer much implement this function.
+ *
+ * @return Value of the given register.
+ */
+u32 nvgpu_os_readl(uintptr_t addr);
+/**
+ * @brief Write a value to a register with an ordering constraint.
+ *
+ * @param v [in]		Value to write at the offset.
+ * @param addr [in]     Register cpu virtual address.
+ *
+ * Write a 32-bit value to the register cpu virtual address with an
+ * ordering constraint on memory operations.
+ * OS layer much implement this function.
+ *
+ * @return None.
+ */
+void nvgpu_os_writel(u32 v, uintptr_t addr);
+/**
+ * @brief Write a value to a register without an ordering constraint.
+ *
+ * @param v [in]		Value to write at the offset.
+ * @param addr [in]     Register cpu virtual address.
+ *
+ * Write a 32-bit value to the register cpu virtual address without an
+ * ordering constraint on memory operations.
+ * OS layer much implement this function.
+ *
+ * @return None.
+ */
+void nvgpu_os_writel_relaxed(u32 v, uintptr_t addr);
+
 /**
  * @file
  *
@@ -65,8 +103,7 @@ void nvgpu_writel(struct gk20a *g, u32 r, u32 v);
  * @param v [in]		Value to write at the offset.
  *
  * Write a 32-bit value to register offset in GPU IO space without
- * an ordering constraint on memory operations. This function is
- * implemented by the OS layer.
+ * an ordering constraint on memory operations.
  *
  * @return None.
  */
diff --git a/drivers/gpu/nvgpu/include/nvgpu/posix/io.h b/drivers/gpu/nvgpu/include/nvgpu/posix/io.h
index 4e82dd985..07b5f1963 100644
--- a/drivers/gpu/nvgpu/include/nvgpu/posix/io.h
+++ b/drivers/gpu/nvgpu/include/nvgpu/posix/io.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2019, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2018-2021, NVIDIA CORPORATION.  All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -72,6 +72,18 @@ struct nvgpu_posix_io_callbacks *nvgpu_posix_register_io(
 	struct gk20a *g,
 	struct nvgpu_posix_io_callbacks *io_callbacks);
 
+/**
+ * The high 4 bits of the register mapped address are used for identify which
+ * register aperture it tries to access.
+ * In nvgpu_os_writel/readl, it uses the high 4 bits to call different
+ * callbacks, like nvgpu_readl/writel or nvgpu_bar1_readl/writel.
+ */
+#define NVGPU_POSIX_REG_SHIFT 60
+#define NVGPU_POSIX_REG_MASK 0xfULL
+#define NVGPU_POSIX_REG_BAR0 1ULL
+#define NVGPU_POSIX_REG_BAR1 2ULL
+#define NVGPU_POSIX_REG_USERMODE 3ULL
+
 struct nvgpu_posix_io_reg_space {
 	u32 base;
 	u32 size;
diff --git a/drivers/gpu/nvgpu/include/nvgpu/posix/probe.h b/drivers/gpu/nvgpu/include/nvgpu/posix/probe.h
index 0b823fe6a..71a71ac06 100644
--- a/drivers/gpu/nvgpu/include/nvgpu/posix/probe.h
+++ b/drivers/gpu/nvgpu/include/nvgpu/posix/probe.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2018-2021, NVIDIA CORPORATION.  All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -36,6 +36,7 @@
 
 struct gk20a;
 
+struct gk20a *nvgpu_posix_current_device(void);
 struct gk20a *nvgpu_posix_probe(void);
 void nvgpu_posix_cleanup(struct gk20a *g);
 
diff --git a/drivers/gpu/nvgpu/os/linux/driver_common.c b/drivers/gpu/nvgpu/os/linux/driver_common.c
index 5e44ad529..1f1daf957 100644
--- a/drivers/gpu/nvgpu/os/linux/driver_common.c
+++ b/drivers/gpu/nvgpu/os/linux/driver_common.c
@@ -82,8 +82,8 @@ static void nvgpu_init_vars(struct gk20a *g)
 	nvgpu_mutex_init(&l->ctrl_privs_lock);
 	nvgpu_init_list_node(&l->ctrl_privs);
 
-	l->regs_saved = l->regs;
-	l->bar1_saved = l->bar1;
+	g->regs_saved = g->regs;
+	g->bar1_saved = g->bar1;
 
 	g->emc3d_ratio = EMC3D_DEFAULT_RATIO;
 
diff --git a/drivers/gpu/nvgpu/os/linux/io_usermode.c b/drivers/gpu/nvgpu/os/linux/io_usermode.c
index 9132b372e..b851f176b 100644
--- a/drivers/gpu/nvgpu/os/linux/io_usermode.c
+++ b/drivers/gpu/nvgpu/os/linux/io_usermode.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2018, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2017-2021, NVIDIA CORPORATION.  All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
@@ -19,9 +19,8 @@
 
 void nvgpu_usermode_writel(struct gk20a *g, u32 r, u32 v)
 {
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-	void __iomem *reg = l->usermode_regs + (r - g->ops.usermode.base(g));
+	uintptr_t reg = g->usermode_regs + (r - g->ops.usermode.base(g));
 
-	writel_relaxed(v, reg);
+	nvgpu_os_writel_relaxed(v, reg);
 	nvgpu_log(g, gpu_dbg_reg, "usermode r=0x%x v=0x%x", r, v);
 }
diff --git a/drivers/gpu/nvgpu/os/linux/ioctl_ctrl.c b/drivers/gpu/nvgpu/os/linux/ioctl_ctrl.c
index 16770d021..a5d5a4dbe 100644
--- a/drivers/gpu/nvgpu/os/linux/ioctl_ctrl.c
+++ b/drivers/gpu/nvgpu/os/linux/ioctl_ctrl.c
@@ -2278,7 +2278,7 @@ int gk20a_ctrl_dev_mmap(struct file *filp, struct vm_area_struct *vma)
 	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 
 	err = io_remap_pfn_range(vma, vma->vm_start,
-			l->usermode_regs_bus_addr >> PAGE_SHIFT,
+			g->usermode_regs_bus_addr >> PAGE_SHIFT,
 			vma->vm_end - vma->vm_start, vma->vm_page_prot);
 	if (!err) {
 		priv->usermode_vma.vma = vma;
@@ -2297,7 +2297,6 @@ static void alter_usermode_mapping(struct gk20a *g,
 		struct gk20a_ctrl_priv *priv,
 		bool poweroff)
 {
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
 	struct vm_area_struct *vma = priv->usermode_vma.vma;
 	bool vma_mapped = priv->usermode_vma.vma_mapped;
 	int err;
@@ -2335,7 +2334,7 @@ static void alter_usermode_mapping(struct gk20a *g,
 	} else if (!poweroff && !vma_mapped) {
 		vma->vm_flags = priv->usermode_vma.flags;
 		err = io_remap_pfn_range(vma, vma->vm_start,
-				l->usermode_regs_bus_addr >> PAGE_SHIFT,
+				g->usermode_regs_bus_addr >> PAGE_SHIFT,
 				vma->vm_end - vma->vm_start, vma->vm_page_prot);
 		if (err != 0) {
 			nvgpu_err(g, "can't restore usermode mapping");
diff --git a/drivers/gpu/nvgpu/os/linux/linux-io.c b/drivers/gpu/nvgpu/os/linux/linux-io.c
index efe4af28a..8613950c9 100644
--- a/drivers/gpu/nvgpu/os/linux/linux-io.c
+++ b/drivers/gpu/nvgpu/os/linux/linux-io.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2019, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2017-2021, NVIDIA CORPORATION.  All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
@@ -12,125 +12,20 @@
  */
 
 #include <nvgpu/io.h>
-#include <nvgpu/types.h>
-#include <nvgpu/gk20a.h>
-#include <nvgpu/nvgpu_init.h>
 
 #include "os_linux.h"
 
-static void nvgpu_warn_on_no_regs(void)
+u32 nvgpu_os_readl(uintptr_t addr)
 {
-	WARN_ONCE(true, "Attempted access to GPU regs after unmapping!");
+	return readl((void __iomem *)addr);
 }
 
-void nvgpu_writel(struct gk20a *g, u32 r, u32 v)
+void nvgpu_os_writel(u32 v, uintptr_t addr)
 {
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-
-	if (unlikely(!l->regs)) {
-		nvgpu_warn_on_no_regs();
-		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x (failed)", r, v);
-	} else {
-		writel_relaxed(v, l->regs + r);
-		nvgpu_wmb();
-		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x", r, v);
-	}
+	writel(v, (void __iomem *)addr);
 }
 
-void nvgpu_writel_relaxed(struct gk20a *g, u32 r, u32 v)
+void nvgpu_os_writel_relaxed(u32 v, uintptr_t addr)
 {
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-
-	if (unlikely(!l->regs)) {
-		nvgpu_warn_on_no_regs();
-		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x (failed)", r, v);
-	} else {
-		writel_relaxed(v, l->regs + r);
-	}
-}
-
-u32 nvgpu_readl(struct gk20a *g, u32 r)
-{
-	u32 v = nvgpu_readl_impl(g, r);
-
-	if (v == 0xffffffff)
-		nvgpu_check_gpu_state(g);
-
-	return v;
-}
-
-u32 nvgpu_readl_impl(struct gk20a *g, u32 r)
-{
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-	u32 v = 0xffffffff;
-
-	if (unlikely(!l->regs)) {
-		nvgpu_warn_on_no_regs();
-		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x (failed)", r, v);
-	} else {
-		v = readl(l->regs + r);
-		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x", r, v);
-	}
-
-	return v;
-}
-
-void nvgpu_writel_loop(struct gk20a *g, u32 r, u32 v)
-{
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-
-	if (unlikely(!l->regs)) {
-		nvgpu_warn_on_no_regs();
-		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x (failed)", r, v);
-	} else {
-		nvgpu_wmb();
-		do {
-			writel_relaxed(v, l->regs + r);
-		} while (readl(l->regs + r) != v);
-		nvgpu_log(g, gpu_dbg_reg, "r=0x%x v=0x%x", r, v);
-	}
-}
-
-void nvgpu_bar1_writel(struct gk20a *g, u32 b, u32 v)
-{
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-
-	if (unlikely(!l->bar1)) {
-		nvgpu_warn_on_no_regs();
-		nvgpu_log(g, gpu_dbg_reg, "b=0x%x v=0x%x (failed)", b, v);
-	} else {
-		nvgpu_wmb();
-		writel_relaxed(v, l->bar1 + b);
-		nvgpu_log(g, gpu_dbg_reg, "b=0x%x v=0x%x", b, v);
-	}
-}
-
-u32 nvgpu_bar1_readl(struct gk20a *g, u32 b)
-{
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-	u32 v = 0xffffffff;
-
-	if (unlikely(!l->bar1)) {
-		nvgpu_warn_on_no_regs();
-		nvgpu_log(g, gpu_dbg_reg, "b=0x%x v=0x%x (failed)", b, v);
-	} else {
-		v = readl(l->bar1 + b);
-		nvgpu_log(g, gpu_dbg_reg, "b=0x%x v=0x%x", b, v);
-	}
-
-	return v;
-}
-
-bool nvgpu_io_exists(struct gk20a *g)
-{
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-
-	return l->regs != NULL;
-}
-
-bool nvgpu_io_valid_reg(struct gk20a *g, u32 r)
-{
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-
-	return r < resource_size(l->regs);
+	writel_relaxed(v, (void __iomem *)addr);
 }
diff --git a/drivers/gpu/nvgpu/os/linux/module.c b/drivers/gpu/nvgpu/os/linux/module.c
index 610a5c9d0..88b104d30 100644
--- a/drivers/gpu/nvgpu/os/linux/module.c
+++ b/drivers/gpu/nvgpu/os/linux/module.c
@@ -229,10 +229,8 @@ void gk20a_idle(struct gk20a *g)
  */
 static int gk20a_restore_registers(struct gk20a *g)
 {
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-
-	l->regs = l->regs_saved;
-	l->bar1 = l->bar1_saved;
+	g->regs = g->regs_saved;
+	g->bar1 = g->bar1_saved;
 
 	nvgpu_restore_usermode_registers(g);
 
@@ -547,10 +545,8 @@ done:
  */
 static int gk20a_lockout_registers(struct gk20a *g)
 {
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-
-	l->regs = NULL;
-	l->bar1 = NULL;
+	g->regs = 0U;
+	g->bar1 = 0U;
 
 	nvgpu_lockout_usermode_registers(g);
 
@@ -1014,37 +1010,41 @@ static int gk20a_init_support(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct gk20a *g = get_gk20a(dev);
 	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
+	void __iomem *addr;
 	int err = -ENOMEM;
 
 #ifdef CONFIG_NVGPU_VPR
 	tegra_register_idle_unidle(gk20a_do_idle, gk20a_do_unidle, g);
 #endif
 
-	l->regs = nvgpu_devm_ioremap_resource(pdev,
+	addr = nvgpu_devm_ioremap_resource(pdev,
 					      GK20A_BAR0_IORESOURCE_MEM,
 					      &l->reg_mem);
-	if (IS_ERR(l->regs)) {
+	if (IS_ERR(addr)) {
 		nvgpu_err(g, "failed to remap gk20a registers");
-		err = PTR_ERR(l->regs);
+		err = PTR_ERR(addr);
 		goto fail;
 	}
+	g->regs = (uintptr_t)addr;
+	g->regs_size = resource_size(l->reg_mem);
 
-	l->regs_bus_addr = nvgpu_resource_addr(pdev,
+	g->regs_bus_addr = nvgpu_resource_addr(pdev,
 			GK20A_BAR0_IORESOURCE_MEM);
-	if (!l->regs_bus_addr) {
+	if (!g->regs_bus_addr) {
 		nvgpu_err(g, "failed to read register bus offset");
 		err = -ENODEV;
 		goto fail;
 	}
 
-	l->bar1 = nvgpu_devm_ioremap_resource(pdev,
+	addr = nvgpu_devm_ioremap_resource(pdev,
 					      GK20A_BAR1_IORESOURCE_MEM,
 					      &l->bar1_mem);
-	if (IS_ERR(l->bar1)) {
+	if (IS_ERR(addr)) {
 		nvgpu_err(g, "failed to remap gk20a bar1");
-		err = PTR_ERR(l->bar1);
+		err = PTR_ERR(addr);
 		goto fail;
 	}
+	g->bar1 = (uintptr_t)addr;
 
 	err = nvgpu_init_sim_support_linux(g, pdev);
 	if (err)
@@ -1059,11 +1059,11 @@ static int gk20a_init_support(struct platform_device *pdev)
 fail_sim:
 	nvgpu_remove_sim_support_linux(g);
 fail:
-	if (l->regs)
-		l->regs = NULL;
+	if (g->regs)
+		g->regs = 0U;
 
-	if (l->bar1)
-		l->bar1 = NULL;
+	if (g->bar1)
+		g->bar1 = 0U;
 
 	return err;
 }
diff --git a/drivers/gpu/nvgpu/os/linux/module_usermode.c b/drivers/gpu/nvgpu/os/linux/module_usermode.c
index 2babce43f..073518991 100644
--- a/drivers/gpu/nvgpu/os/linux/module_usermode.c
+++ b/drivers/gpu/nvgpu/os/linux/module_usermode.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2020, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2017-2021, NVIDIA CORPORATION.  All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
@@ -27,9 +27,7 @@
  */
 void nvgpu_lockout_usermode_registers(struct gk20a *g)
 {
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-
-	l->usermode_regs = NULL;
+	g->usermode_regs = 0U;
 }
 
 /*
@@ -37,33 +35,27 @@ void nvgpu_lockout_usermode_registers(struct gk20a *g)
  */
 void nvgpu_restore_usermode_registers(struct gk20a *g)
 {
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-
-	l->usermode_regs = l->usermode_regs_saved;
+	g->usermode_regs = g->usermode_regs_saved;
 }
 
 void nvgpu_remove_usermode_support(struct gk20a *g)
 {
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-
-	if (l->usermode_regs) {
-		l->usermode_regs = NULL;
+	if (g->usermode_regs) {
+		g->usermode_regs = 0U;
 	}
 }
 
 void nvgpu_init_usermode_support(struct gk20a *g)
 {
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-
 	if (g->ops.usermode.base == NULL) {
 		return;
 	}
 
-	if (l->usermode_regs == NULL) {
-		l->usermode_regs = l->regs + g->ops.usermode.bus_base(g);
-		l->usermode_regs_saved = l->usermode_regs;
+	if (g->usermode_regs == 0U) {
+		g->usermode_regs = g->regs + g->ops.usermode.bus_base(g);
+		g->usermode_regs_saved = g->usermode_regs;
 	}
 
-	l->usermode_regs_bus_addr = l->regs_bus_addr +
+	g->usermode_regs_bus_addr = g->regs_bus_addr +
 					g->ops.usermode.bus_base(g);
 }
diff --git a/drivers/gpu/nvgpu/os/linux/os_linux.h b/drivers/gpu/nvgpu/os/linux/os_linux.h
index 439f907ea..329a29d0f 100644
--- a/drivers/gpu/nvgpu/os/linux/os_linux.h
+++ b/drivers/gpu/nvgpu/os/linux/os_linux.h
@@ -96,17 +96,7 @@ struct nvgpu_os_linux {
 	struct workqueue_struct *nonstall_work_queue;
 
 	struct resource *reg_mem;
-	void __iomem *regs;
-	void __iomem *regs_saved;
-	u64 regs_bus_addr;
-
 	struct resource *bar1_mem;
-	void __iomem *bar1;
-	void __iomem *bar1_saved;
-
-	void __iomem *usermode_regs;
-	void __iomem *usermode_regs_saved;
-	u64 usermode_regs_bus_addr;
 
 	struct nvgpu_os_linux_ops ops;
 
diff --git a/drivers/gpu/nvgpu/os/linux/pci.c b/drivers/gpu/nvgpu/os/linux/pci.c
index b1e72528a..6484dfbc8 100644
--- a/drivers/gpu/nvgpu/os/linux/pci.c
+++ b/drivers/gpu/nvgpu/os/linux/pci.c
@@ -354,31 +354,34 @@ static int nvgpu_pci_init_support(struct pci_dev *pdev)
 {
 	int err = 0;
 	struct gk20a *g = get_gk20a(&pdev->dev);
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
 	struct device *dev = &pdev->dev;
+	void __iomem *addr;
 
-	l->regs = nvgpu_devm_ioremap(dev, pci_resource_start(pdev, 0),
+	addr = nvgpu_devm_ioremap(dev, pci_resource_start(pdev, 0),
 				     pci_resource_len(pdev, 0));
-	if (IS_ERR(l->regs)) {
+	if (IS_ERR(addr)) {
 		nvgpu_err(g, "failed to remap gk20a registers");
-		err = PTR_ERR(l->regs);
+		err = PTR_ERR(addr);
 		goto fail;
 	}
+	g->regs = (uintptr_t)addr;
+	g->regs_size = pci_resource_len(pdev, 0);
 
-	l->regs_bus_addr = pci_resource_start(pdev, 0);
-	if (!l->regs_bus_addr) {
+	g->regs_bus_addr = pci_resource_start(pdev, 0);
+	if (!g->regs_bus_addr) {
 		nvgpu_err(g, "failed to read register bus offset");
 		err = -ENODEV;
 		goto fail;
 	}
 
-	l->bar1 = nvgpu_devm_ioremap(dev, pci_resource_start(pdev, 1),
+	addr = nvgpu_devm_ioremap(dev, pci_resource_start(pdev, 1),
 				     pci_resource_len(pdev, 1));
-	if (IS_ERR(l->bar1)) {
+	if (IS_ERR(addr)) {
 		nvgpu_err(g, "failed to remap gk20a bar1");
-		err = PTR_ERR(l->bar1);
+		err = PTR_ERR(addr);
 		goto fail;
 	}
+	g->bar1 = (uintptr_t)addr;
 
 	err = nvgpu_init_sim_support_linux_pci(g);
 	if (err)
@@ -392,11 +395,11 @@ static int nvgpu_pci_init_support(struct pci_dev *pdev)
  fail_sim:
 	nvgpu_remove_sim_support_linux_pci(g);
  fail:
-	if (l->regs)
-		l->regs = NULL;
+	if (g->regs)
+		g->regs = 0U;
 
-	if (l->bar1)
-		l->bar1 = NULL;
+	if (g->bar1)
+		g->bar1 = 0U;
 
 	return err;
 }
diff --git a/drivers/gpu/nvgpu/os/linux/sim_pci.c b/drivers/gpu/nvgpu/os/linux/sim_pci.c
index 9ff72f935..ef55f447c 100644
--- a/drivers/gpu/nvgpu/os/linux/sim_pci.c
+++ b/drivers/gpu/nvgpu/os/linux/sim_pci.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2019, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2017-2021, NVIDIA CORPORATION.  All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
@@ -75,7 +75,6 @@ void nvgpu_remove_sim_support_linux_pci(struct gk20a *g)
 
 int nvgpu_init_sim_support_linux_pci(struct gk20a *g)
 {
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
 	struct sim_nvgpu_linux *sim_linux;
 	int err = -ENOMEM;
 	bool is_simulation;
@@ -91,7 +90,7 @@ int nvgpu_init_sim_support_linux_pci(struct gk20a *g)
 		return err;
 	g->sim = &sim_linux->sim;
 	g->sim->g = g;
-	sim_linux->regs = l->regs + sim_r();
+	sim_linux->regs = (void __iomem *)g->regs + sim_r();
 	sim_linux->remove_support_linux = nvgpu_remove_sim_support_linux_pci;
 
 	return 0;
diff --git a/drivers/gpu/nvgpu/os/linux/vgpu/gv11b/platform_gv11b_vgpu_tegra.c b/drivers/gpu/nvgpu/os/linux/vgpu/gv11b/platform_gv11b_vgpu_tegra.c
index ba0bdfec8..f6afb3c99 100644
--- a/drivers/gpu/nvgpu/os/linux/vgpu/gv11b/platform_gv11b_vgpu_tegra.c
+++ b/drivers/gpu/nvgpu/os/linux/vgpu/gv11b/platform_gv11b_vgpu_tegra.c
@@ -33,7 +33,6 @@ int gv11b_vgpu_probe(struct device *dev)
 	struct gk20a_platform *platform = dev_get_drvdata(dev);
 	struct resource *r;
 	void __iomem *regs;
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(platform->g);
 	struct gk20a *g = platform->g;
 #ifdef CONFIG_TEGRA_GK20A_NVHOST
 	int ret;
@@ -49,14 +48,14 @@ int gv11b_vgpu_probe(struct device *dev)
 		nvgpu_err(g, "failed to map usermode regs");
 		return PTR_ERR(regs);
 	}
-	l->usermode_regs = regs;
+	g->usermode_regs = (uintptr_t)regs;
 
-	l->usermode_regs_bus_addr = r->start;
+	g->usermode_regs_bus_addr = r->start;
 
 #ifdef CONFIG_TEGRA_GK20A_NVHOST
 	ret = nvgpu_get_nvhost_dev(g);
 	if (ret) {
-		l->usermode_regs = NULL;
+		g->usermode_regs = 0U;
 		return ret;
 	}
 
diff --git a/drivers/gpu/nvgpu/os/linux/vgpu/vgpu_linux.c b/drivers/gpu/nvgpu/os/linux/vgpu/vgpu_linux.c
index 5665eb012..c154c5886 100644
--- a/drivers/gpu/nvgpu/os/linux/vgpu/vgpu_linux.c
+++ b/drivers/gpu/nvgpu/os/linux/vgpu/vgpu_linux.c
@@ -72,15 +72,13 @@ struct vgpu_priv_data *vgpu_get_priv_data(struct gk20a *g)
 
 static void vgpu_remove_support(struct gk20a *g)
 {
-	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
-
 	vgpu_remove_support_common(g);
 
 	/* free mappings to registers, etc*/
 
-	if (l->bar1) {
-		iounmap(l->bar1);
-		l->bar1 = NULL;
+	if (g->bar1) {
+		iounmap((void __iomem *)g->bar1);
+		g->bar1 = 0U;
 	}
 }
 
@@ -101,8 +99,8 @@ static void vgpu_init_vars(struct gk20a *g, struct gk20a_platform *platform)
 	nvgpu_mutex_init(&l->ctrl_privs_lock);
 	nvgpu_init_list_node(&l->ctrl_privs);
 
-	l->regs_saved = l->regs;
-	l->bar1_saved = l->bar1;
+	g->regs_saved = g->regs;
+	g->bar1_saved = g->bar1;
 
 	nvgpu_atomic_set(&g->clk_arb_global_nr, 0);
 
@@ -140,7 +138,7 @@ static int vgpu_init_support(struct platform_device *pdev)
 			err = PTR_ERR(regs);
 			goto fail;
 		}
-		l->bar1 = regs;
+		g->bar1 = (uintptr_t)regs;
 		l->bar1_mem = r;
 	}
 
diff --git a/drivers/gpu/nvgpu/os/posix/nvgpu.c b/drivers/gpu/nvgpu/os/posix/nvgpu.c
index 0331223bf..c16d027ea 100644
--- a/drivers/gpu/nvgpu/os/posix/nvgpu.c
+++ b/drivers/gpu/nvgpu/os/posix/nvgpu.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2018-2021, NVIDIA CORPORATION.  All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -218,6 +218,12 @@ static void nvgpu_posix_load_regs(struct gk20a *g)
 	}
 }
 
+static __thread struct gk20a *g_saved;
+struct gk20a *nvgpu_posix_current_device(void)
+{
+	return g_saved;
+}
+
 /*
  * This function aims to initialize enough stuff to make unit testing worth
  * while. There are several interfaces and APIs that rely on the struct gk20a's
@@ -251,6 +257,12 @@ struct gk20a *nvgpu_posix_probe(void)
 	g->log_mask = NVGPU_DEFAULT_DBG_MASK;
 	g->mm.g = g;
 
+	g_saved = g;
+
+	g->regs = NVGPU_POSIX_REG_BAR0 << NVGPU_POSIX_REG_SHIFT;
+	g->bar1 = NVGPU_POSIX_REG_BAR1 << NVGPU_POSIX_REG_SHIFT;
+	g->usermode_regs = NVGPU_POSIX_REG_USERMODE << NVGPU_POSIX_REG_SHIFT;
+
 	if (nvgpu_kmem_init(g) != 0) {
 		goto fail_kmem;
 	}
diff --git a/drivers/gpu/nvgpu/os/posix/posix-io.c b/drivers/gpu/nvgpu/os/posix/posix-io.c
index 202193acc..078ee02b7 100644
--- a/drivers/gpu/nvgpu/os/posix/posix-io.c
+++ b/drivers/gpu/nvgpu/os/posix/posix-io.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2018-2021, NVIDIA CORPORATION.  All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -26,6 +26,7 @@
 
 #include <nvgpu/posix/io.h>
 #include <nvgpu/posix/posix-fault-injection.h>
+#include <nvgpu/posix/probe.h>
 
 #include "os_posix.h"
 
@@ -59,7 +60,7 @@ struct nvgpu_posix_io_callbacks *nvgpu_posix_register_io(
 	return old_io;
 }
 
-void nvgpu_writel(struct gk20a *g, u32 r, u32 v)
+static void nvgpu_posix_writel(struct gk20a *g, u32 r, u32 v)
 {
 	struct nvgpu_posix_io_callbacks *callbacks =
 		nvgpu_os_posix_from_gk20a(g)->callbacks;
@@ -76,14 +77,7 @@ void nvgpu_writel(struct gk20a *g, u32 r, u32 v)
 	callbacks->writel(g, &access);
 }
 
-#ifdef CONFIG_NVGPU_DGPU
-void nvgpu_writel_relaxed(struct gk20a *g, u32 r, u32 v)
-{
-	nvgpu_writel(g, r, v);
-}
-#endif
-
-u32 nvgpu_readl(struct gk20a *g, u32 r)
+static u32 nvgpu_posix_readl(struct gk20a *g, u32 r)
 {
 	struct nvgpu_posix_io_callbacks *callbacks =
 		nvgpu_os_posix_from_gk20a(g)->callbacks;
@@ -109,33 +103,7 @@ u32 nvgpu_readl(struct gk20a *g, u32 r)
 	return access.value;
 }
 
-#ifdef CONFIG_NVGPU_NON_FUSA
-void nvgpu_writel_loop(struct gk20a *g, u32 r, u32 v)
-{
-	BUG();
-}
-#endif
-
-u32 nvgpu_readl_impl(struct gk20a *g, u32 r)
-{
-	struct nvgpu_posix_io_callbacks *callbacks =
-		nvgpu_os_posix_from_gk20a(g)->callbacks;
-
-	struct nvgpu_reg_access access = {
-		.addr = r,
-		.value = 0L
-	};
-
-	if (callbacks == NULL || callbacks->__readl == NULL) {
-		BUG();
-	}
-
-	callbacks->__readl(g, &access);
-
-	return access.value;
-}
-
-void nvgpu_bar1_writel(struct gk20a *g, u32 b, u32 v)
+static void nvgpu_posix_bar1_writel(struct gk20a *g, u32 b, u32 v)
 {
 	struct nvgpu_posix_io_callbacks *callbacks =
 		nvgpu_os_posix_from_gk20a(g)->callbacks;
@@ -152,7 +120,7 @@ void nvgpu_bar1_writel(struct gk20a *g, u32 b, u32 v)
 	callbacks->bar1_writel(g, &access);
 }
 
-u32 nvgpu_bar1_readl(struct gk20a *g, u32 b)
+static u32 nvgpu_posix_bar1_readl(struct gk20a *g, u32 b)
 {
 	struct nvgpu_posix_io_callbacks *callbacks =
 		nvgpu_os_posix_from_gk20a(g)->callbacks;
@@ -188,14 +156,44 @@ void nvgpu_usermode_writel(struct gk20a *g, u32 r, u32 v)
 	callbacks->usermode_writel(g, &access);
 }
 
-bool nvgpu_io_exists(struct gk20a *g)
+u32 nvgpu_os_readl(uintptr_t addr)
 {
-	return false;
+	struct gk20a *g = nvgpu_posix_current_device();
+	u32 r, type;
+
+	r = (u32)(addr & ~(NVGPU_POSIX_REG_MASK << NVGPU_POSIX_REG_SHIFT));
+	type = (u32)(addr >> NVGPU_POSIX_REG_SHIFT);
+	switch (type) {
+	case NVGPU_POSIX_REG_BAR0:
+		return nvgpu_posix_readl(g, r);
+	case NVGPU_POSIX_REG_BAR1:
+		return nvgpu_posix_bar1_readl(g, r);
+	default:
+		BUG();
+	}
 }
 
-bool nvgpu_io_valid_reg(struct gk20a *g, u32 r)
+void nvgpu_os_writel(u32 v, uintptr_t addr)
 {
-	return false;
+	struct gk20a *g = nvgpu_posix_current_device();
+	u32 r;
+	u64 type;
+
+	r = (u32)(addr & ~(NVGPU_POSIX_REG_MASK << NVGPU_POSIX_REG_SHIFT));
+	type = addr >> NVGPU_POSIX_REG_SHIFT;
+	switch (type) {
+	case NVGPU_POSIX_REG_BAR0:
+		return nvgpu_posix_writel(g, r, v);
+	case NVGPU_POSIX_REG_BAR1:
+		return nvgpu_posix_bar1_writel(g, r, v);
+	default:
+		BUG();
+	}
+}
+
+void nvgpu_os_writel_relaxed(u32 v, uintptr_t addr)
+{
+	nvgpu_os_writel(v, addr);
 }
 
 void nvgpu_posix_io_init_reg_space(struct gk20a *g)