text: /*
   * PowerNV OPAL in-memory console interface
   *
   * Copyright 2014 IBM Corp.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   */
  
  #include <asm/io.h>
  #include <asm/opal.h>
  #include <linux/debugfs.h>
  #include <linux/of.h>
  #include <linux/types.h>
  #include <asm/barrier.h>
  
  /* OPAL in-memory console. Defined in OPAL source at core/console.c */
  struct memcons {
  	__be64 magic;
  #define MEMCONS_MAGIC	0x6630696567726173L
  	__be64 obuf_phys;
  	__be64 ibuf_phys;
  	__be32 obuf_size;
  	__be32 ibuf_size;
  	__be32 out_pos;
  #define MEMCONS_OUT_POS_WRAP	0x80000000u
  #define MEMCONS_OUT_POS_MASK	0x00ffffffu
  	__be32 in_prod;
  	__be32 in_cons;
  };
  
  static ssize_t opal_msglog_read(struct file *file, struct kobject *kobj,
  				struct bin_attribute *bin_attr, char *to,
  				loff_t pos, size_t count)
  {
  	struct memcons *mc = bin_attr->private;
  	const char *conbuf;
  	ssize_t ret;
  	size_t first_read = 0;
  	uint32_t out_pos, avail;
  
  	if (!mc)
  		return -ENODEV;
  
  	out_pos = be32_to_cpu(ACCESS_ONCE(mc->out_pos));
  
  	/* Now we've read out_pos, put a barrier in before reading the new
  	 * data it points to in conbuf. */
  	smp_rmb();
  
  	conbuf = phys_to_virt(be64_to_cpu(mc->obuf_phys));
  
  	/* When the buffer has wrapped, read from the out_pos marker to the end
  	 * of the buffer, and then read the remaining data as in the un-wrapped
  	 * case. */
  	if (out_pos & MEMCONS_OUT_POS_WRAP) {
  
  		out_pos &= MEMCONS_OUT_POS_MASK;
  		avail = be32_to_cpu(mc->obuf_size) - out_pos;
  
  		ret = memory_read_from_buffer(to, count, &pos,
  				conbuf + out_pos, avail);
  
  		if (ret < 0)
  			goto out;
  
  		first_read = ret;
  		to += first_read;
  		count -= first_read;
  		pos -= avail;
  
  		if (count <= 0)
  			goto out;
  	}
  
  	/* Sanity check. The firmware should not do this to us. */
  	if (out_pos > be32_to_cpu(mc->obuf_size)) {
  		pr_err("OPAL: memory console corruption. Aborting read.\n");
  		return -EINVAL;
  	}
  
  	ret = memory_read_from_buffer(to, count, &pos, conbuf, out_pos);
  
  	if (ret < 0)
  		goto out;
  
  	ret += first_read;
  out:
  	return ret;
  }
  
  static struct bin_attribute opal_msglog_attr = {
  	.attr = {.name = "msglog", .mode = 0444},
  	.read = opal_msglog_read
  };
  
  void __init opal_msglog_init(void)
  {
  	u64 mcaddr;
  	struct memcons *mc;
  
  	if (of_property_read_u64(opal_node, "ibm,opal-memcons", &mcaddr)) {
  		pr_warn("OPAL: Property ibm,opal-memcons not found, no message log\n");
  		return;
  	}
  
  	mc = phys_to_virt(mcaddr);
  	if (!mc) {
  		pr_warn("OPAL: memory console address is invalid\n");
  		return;
  	}
  
  	if (be64_to_cpu(mc->magic) != MEMCONS_MAGIC) {
  		pr_warn("OPAL: memory console version is invalid\n");
  		return;
  	}
  
  	opal_msglog_attr.private = mc;
  
  	if (sysfs_create_bin_file(opal_kobj, &opal_msglog_attr) != 0)
  		pr_warn("OPAL: sysfs file creation failed\n");
  }
  