// SPDX-License-Identifier: GPL-2.0-only
  /*
   * A generic version of devmem_is_allowed.
   *
   * Based on arch/arm64/mm/mmap.c
   *
   * Copyright (C) 2020 Google, Inc.
   * Copyright (C) 2012 ARM Ltd.
   */
  
  #include <linux/mm.h>
  #include <linux/ioport.h>
  
  /*
   * devmem_is_allowed() checks to see if /dev/mem access to a certain address
   * is valid. The argument is a physical page number.  We mimic x86 here by
   * disallowing access to system RAM as well as device-exclusive MMIO regions.
   * This effectively disable read()/write() on /dev/mem.
   */
  int devmem_is_allowed(unsigned long pfn)
  {
  	if (iomem_is_exclusive(pfn << PAGE_SHIFT))
  		return 0;
  	if (!page_is_ram(pfn))
  		return 1;
  	return 0;
  }