linux/kernel/power/console.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Functions for saving/restoring console.
 *
 * Originally from swsusp.
 */

#include <linux/console.h>
#include <linux/vt_kern.h>
#include <linux/kbd_kern.h>
#include <linux/vt.h>
#include <linux/module.h>
#include <linux/slab.h>
#include "power.h"

#define SUSPEND_CONSOLE …

static int orig_fgconsole, orig_kmsg;

static DEFINE_MUTEX(vt_switch_mutex);

struct pm_vt_switch { … };

static LIST_HEAD(pm_vt_switch_list);


/**
 * pm_vt_switch_required - indicate VT switch at suspend requirements
 * @dev: device
 * @required: if true, caller needs VT switch at suspend/resume time
 *
 * The different console drivers may or may not require VT switches across
 * suspend/resume, depending on how they handle restoring video state and
 * what may be running.
 *
 * Drivers can indicate support for switchless suspend/resume, which can
 * save time and flicker, by using this routine and passing 'false' as
 * the argument.  If any loaded driver needs VT switching, or the
 * no_console_suspend argument has been passed on the command line, VT
 * switches will occur.
 */
void pm_vt_switch_required(struct device *dev, bool required)
{ … }
EXPORT_SYMBOL(…);

/**
 * pm_vt_switch_unregister - stop tracking a device's VT switching needs
 * @dev: device
 *
 * Remove @dev from the vt switch list.
 */
void pm_vt_switch_unregister(struct device *dev)
{ … }
EXPORT_SYMBOL(…);

/*
 * There are three cases when a VT switch on suspend/resume are required:
 *   1) no driver has indicated a requirement one way or another, so preserve
 *      the old behavior
 *   2) console suspend is disabled, we want to see debug messages across
 *      suspend/resume
 *   3) any registered driver indicates it needs a VT switch
 *
 * If none of these conditions is present, meaning we have at least one driver
 * that doesn't need the switch, and none that do, we can avoid it to make
 * resume look a little prettier (and suspend too, but that's usually hidden,
 * e.g. when closing the lid on a laptop).
 */
static bool pm_vt_switch(void)
{ … }

void pm_prepare_console(void)
{ … }

void pm_restore_console(void)
{ … }