mm/arch: userspace device mapping support

This patch adds definitions to support user space device mappings
that allows devices like frame buffer to be accessible from user
space in kernel mode.

The are mainly two changes:

- in `mm/`:
  added vm_map_region(), vm_unmap_region() for drivers to do
  device mapping easily.
- in `arch/`:
  extended ARCH_SHM_NPAGES as user-space mapping region size.
  decoupled ARCH_SHM_MAXREGIONS from region size calculations and
  limit its usage only for SysV shm purposes.

Signed-off-by: Yanfeng Liu <yfliu2008@qq.com>

arch/Kconfig

@@ -769,27 +769,17 @@ config ARCH_SHM_MAXREGIONS
 	int "Max shared memory regions"
 	default 1
 	---help---
-		The maximum number of regions that can allocated for the shared
-		memory space.  This hard-coded value permits static allocation of
+		The maximum number of regions that can be used with SysV shared
+		memory interface. This hard-coded value permits static allocation of
 		the shared memory data structures and serves no other purpose.
 		Default is 1.
 
-		The size of the virtual shared memory address space is then
-		determined by the product of the maximum number of regions, the
-		maximum number of pages per region, and the configured size of
-		each page.
-
 config ARCH_SHM_NPAGES
-	int "Max shared memory pages"
+	int "Max size of userspace VM mapping in pages"
 	default 1
 	---help---
-		The maximum number of pages that can allocated per region for the shared memory
-		region. Default is 1.
-
-		The size of the virtual shared memory address space is then
-		determined by the product of the maximum number of regions, the
-		maximum number of pages per region, and the configured size of
-		each page.
+		The max size of the virtual memory region for shared memory,
+		userspace device mappings etc.
 
 endif # ARCH_VMA_MAPPING
 

include/nuttx/addrenv.h

@@ -190,9 +190,7 @@
 #    define CONFIG_ARCH_SHM_NPAGES 1
 #  endif
 
-#  define ARCH_SHM_MAXPAGES   (CONFIG_ARCH_SHM_NPAGES * CONFIG_ARCH_SHM_MAXREGIONS)
-#  define ARCH_SHM_REGIONSIZE (CONFIG_ARCH_SHM_NPAGES * CONFIG_MM_PGSIZE)
-#  define ARCH_SHM_SIZE       (CONFIG_ARCH_SHM_MAXREGIONS * ARCH_SHM_REGIONSIZE)
+#  define ARCH_SHM_SIZE       (CONFIG_ARCH_SHM_NPAGES * CONFIG_MM_PGSIZE)
 #  define ARCH_SHM_VEND       (CONFIG_ARCH_SHM_VBASE + ARCH_SHM_SIZE - 1)
 
 #  define ARCH_SCRATCH_VBASE   ARCH_SHM_VEND

include/nuttx/mm/map.h

@@ -193,6 +193,45 @@ void vm_release_region(FAR struct mm_map_s *mm, FAR void *vaddr,
 
 #endif
 
+#ifdef CONFIG_ARCH_VMA_MAPPING
+
+/****************************************************************************
+ * Name: vm_map_region
+ *
+ * Description:
+ *   Allocate virtual memory and maps given physical memory into user space
+ *   of the current process.
+ *
+ * Input Parameters:
+ *   paddr - Starting physical address
+ *   size  - Size of the address range
+ *
+ * Returned Value:
+ *   Virtual address if success, or NULL if error
+ *
+ ****************************************************************************/
+
+FAR void *vm_map_region(uintptr_t paddr, size_t size);
+
+/****************************************************************************
+ * Name: vm_unmap_region
+ *
+ * Description:
+ *   Unmap previously mapped userspace device and release the virtual memory.
+ *
+ * Input Parameters:
+ *   vaddr - Starting virtual address of the mapped device
+ *   size - Size of the address range
+ *
+ * Returned Value:
+ *   OK for success or negative value for error
+ *
+ ****************************************************************************/
+
+int vm_unmap_region(FAR void *vaddr, size_t size);
+
+#endif /* CONFIG_ARCH_VMA_MAPPING */
+
 /****************************************************************************
  * Name: mm_map_add
  *

mm/Kconfig

@@ -191,8 +191,9 @@ config MM_SHM
 	depends on MM_PGALLOC && BUILD_KERNEL
 	select ARCH_VMA_MAPPING
 	---help---
-		Build in support for the shared memory interfaces shmget(), shmat(),
-		shmctl(), and shmdt().
+		Build support for mapping physical memory to user-space via
+		shared memory interfaces like shmget(), shmat(), shmctl(),
+		etc, or device mapping interfaces like vm_map_region() etc.
 
 config MM_KMAP
 	bool "Support for dynamic kernel virtual mappings"

mm/map/mm_map.c

@@ -117,8 +117,7 @@ void mm_map_initialize(FAR struct mm_map_s *mm, bool kernel)
   if (!kernel)
     {
       mm->mm_map_vpages = gran_initialize((FAR void *)CONFIG_ARCH_SHM_VBASE,
-                                          ARCH_SHM_MAXPAGES << MM_PGSHIFT,
-                                          MM_PGSHIFT, MM_PGSHIFT);
+                                     ARCH_SHM_SIZE, MM_PGSHIFT, MM_PGSHIFT);
       if (!mm->mm_map_vpages)
         {
           merr("gran_initialize() failed\n");

mm/map/vm_map.c

@@ -0,0 +1,91 @@
+/****************************************************************************
+ * mm/map/vm_map.c
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <debug.h>
+
+#include <nuttx/arch.h>
+#include <nuttx/mm/map.h>
+#include <nuttx/pgalloc.h>
+#include <nuttx/sched.h>
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+#ifdef CONFIG_ARCH_VMA_MAPPING
+
+/* map physical region to userspace */
+
+FAR void *vm_map_region(uintptr_t paddr, size_t size)
+{
+  FAR void *vaddr;
+  uintptr_t tvaddr;
+  uint      i      = 0;
+  int       ret    = OK;
+  size_t    npages = MM_NPAGES(size);
+
+  DEBUGASSERT(npages > 0);
+  DEBUGASSERT(MM_ISALIGNED(paddr));
+
+  vaddr = vm_alloc_region(get_current_mm(), 0, size);
+  if (vaddr)
+    {
+      tvaddr = (uintptr_t)vaddr;
+      for (; i < npages; i++, tvaddr += MM_PGSIZE, paddr += MM_PGSIZE)
+        {
+          ret = up_shmat(&paddr, 1, tvaddr);
+          if (ret)
+            {
+              goto errorout;
+            }
+        }
+    }
+
+  return vaddr;
+
+errorout:
+  if (i)   /* undo mapped pages */
+    {
+      up_shmdt((uintptr_t)vaddr, i);
+    }
+
+  vm_release_region(get_current_mm(), vaddr, size);
+  return 0;
+}
+
+/* unmap userspace device pointer */
+
+int vm_unmap_region(FAR void *vaddr, size_t size)
+{
+  size_t npages = MM_NPAGES(size);
+  int ret;
+
+  DEBUGASSERT(MM_ISALIGNED(vaddr));
+  DEBUGASSERT(npages);
+  ret = up_shmdt((uintptr_t)vaddr, npages);
+  vm_release_region(get_current_mm(), vaddr, size);
+  return ret;
+}
+
+#endif /* CONFIG_ARCH_VMA_MAPPING */