path: root/drivers/tty/hvc/hvcs.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * IBM eServer Hypervisor Virtual Console Server Device Driver
 * Copyright (C) 2003, 2004 IBM Corp.
 *  Ryan S. Arnold (rsa@us.ibm.com)
 *
 * Author(s) :  Ryan S. Arnold <rsa@us.ibm.com>
 *
 * This is the device driver for the IBM Hypervisor Virtual Console Server,
 * "hvcs".  The IBM hvcs provides a tty driver interface to allow Linux
 * user space applications access to the system consoles of logically
 * partitioned operating systems, e.g. Linux, running on the same partitioned
 * Power5 ppc64 system.  Physical hardware consoles per partition are not
 * practical on this hardware so system consoles are accessed by this driver
 * using inter-partition firmware interfaces to virtual terminal devices.
 *
 * A vty is known to the HMC as a "virtual serial server adapter".  It is a
 * virtual terminal device that is created by firmware upon partition creation
 * to act as a partitioned OS's console device.
 *
 * Firmware dynamically (via hotplug) exposes vty-servers to a running ppc64
 * Linux system upon their creation by the HMC or their exposure during boot.
 * The non-user interactive backend of this driver is implemented as a vio
 * device driver so that it can receive notification of vty-server lifetimes
 * after it registers with the vio bus to handle vty-server probe and remove
 * callbacks.
 *
 * Many vty-servers can be configured to connect to one vty, but a vty can
 * only be actively connected to by a single vty-server, in any manner, at one
 * time.  If the HMC is currently hosting the console for a target Linux
 * partition; attempts to open the tty device to the partition's console using
 * the hvcs on any partition will return -EBUSY with every open attempt until
 * the HMC frees the connection between its vty-server and the desired
 * partition's vty device.  Conversely, a vty-server may only be connected to
 * a single vty at one time even though it may have several configured vty
 * partner possibilities.
 *
 * Firmware does not provide notification of vty partner changes to this
 * driver.  This means that an HMC Super Admin may add or remove partner vtys
 * from a vty-server's partner list but the changes will not be signaled to
 * the vty-server.  Firmware only notifies the driver when a vty-server is
 * added or removed from the system.  To compensate for this deficiency, this
 * driver implements a sysfs update attribute which provides a method for
 * rescanning partner information upon a user's request.
 *
 * Each vty-server, prior to being exposed to this driver is reference counted
 * using the 2.6 Linux kernel kref construct.
 *
 * For direction on installation and usage of this driver please reference
 * Documentation/powerpc/hvcs.rst.
 */

#include <linux/device.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/kref.h>
#include <linux/kthread.h>
#include <linux/list.h>
#include <linux/major.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/stat.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <asm/hvconsole.h>
#include <asm/hvcserver.h>
#include <linux/uaccess.h>
#include <asm/vio.h>

/*
 * 1.3.0 -> 1.3.1 In hvcs_open memset(..,0x00,..) instead of memset(..,0x3F,00).
 * Removed braces around single statements following conditionals.  Removed '=
 * 0' after static int declarations since these default to zero.  Removed
 * list_for_each_safe() and replaced with list_for_each_entry() in
 * hvcs_get_by_index().  The 'safe' version is un-needed now that the driver is
 * using spinlocks.  Changed spin_lock_irqsave() to spin_lock() when locking
 * hvcs_structs_lock and hvcs_pi_lock since these are not touched in an int
 * handler.  Initialized hvcs_structs_lock and hvcs_pi_lock to
 * SPIN_LOCK_UNLOCKED at declaration time rather than in hvcs_module_init().
 * Added spin_lock around list_del() in destroy_hvcs_struct() to protect the
 * list traversals from a deletion.  Removed '= NULL' from pointer declaration
 * statements since they are initialized NULL by default.  Removed wmb()
 * instances from hvcs_try_write().  They probably aren't needed with locking in
 * place.  Added check and cleanup for hvcs_pi_buff = kmalloc() in
 * hvcs_module_init().  Exposed hvcs_struct.index via a sysfs attribute so that
 * the coupling between /dev/hvcs* and a vty-server can be automatically
 * determined.  Moved kobject_put() in hvcs_open outside of the
 * spin_unlock_irqrestore().
 *
 * 1.3.1 -> 1.3.2 Changed method for determining hvcs_struct->index and had it
 * align with how the tty layer always assigns the lowest index available.  This
 * change resulted in a list of ints that denotes which indexes are available.
 * Device additions and removals use the new hvcs_get_index() and
 * hvcs_return_index() helper functions.  The list is created with
 * hvsc_alloc_index_list() and it is destroyed with hvcs_free_index_list().
 * Without these fixes hotplug vty-server adapter support goes crazy with this
 * driver if the user removes a vty-server adapter.  Moved free_irq() outside of
 * the hvcs_final_close() function in order to get it out of the spinlock.
 * Rearranged hvcs_close().  Cleaned up some printks and did some housekeeping
 * on the changelog.  Removed local CLC_LENGTH and used HVCS_CLC_LENGTH from
 * arch/powerepc/include/asm/hvcserver.h
 *
 * 1.3.2 -> 1.3.3 Replaced yield() in hvcs_close() with tty_wait_until_sent() to
 * prevent possible lockup with realtime scheduling as similarly pointed out by
 * akpm in hvc_console.  Changed resulted in the removal of hvcs_final_close()
 * to reorder cleanup operations and prevent discarding of pending data during
 * an hvcs_close().  Removed spinlock protection of hvcs_struct data members in
 * hvcs_write_room() and hvcs_cha