arch/arm/mach-lpc32xx/pm.c

Source file repositories/reference/linux-study-clean/arch/arm/mach-lpc32xx/pm.c

File Facts

System
Linux kernel
Corpus path
arch/arm/mach-lpc32xx/pm.c
Extension
.c
Size
4424 bytes
Lines
136
Domain
Architecture Layer
Bucket
arch/arm
Inferred role
Architecture Layer: implementation source
Status
source implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0-only
/*
 * arch/arm/mach-lpc32xx/pm.c
 *
 * Original authors: Vitaly Wool, Dmitry Chigirev <source@mvista.com>
 * Modified by Kevin Wells <kevin.wells@nxp.com>
 *
 * 2005 (c) MontaVista Software, Inc.
 */

/*
 * LPC32XX CPU and system power management
 *
 * The LPC32XX has three CPU modes for controlling system power: run,
 * direct-run, and halt modes. When switching between halt and run modes,
 * the CPU transistions through direct-run mode. For Linux, direct-run
 * mode is not used in normal operation. Halt mode is used when the
 * system is fully suspended.
 *
 * Run mode:
 * The ARM CPU clock (HCLK_PLL), HCLK bus clock, and PCLK bus clocks are
 * derived from the HCLK PLL. The HCLK and PCLK bus rates are divided from
 * the HCLK_PLL rate. Linux runs in this mode.
 *
 * Direct-run mode:
 * The ARM CPU clock, HCLK bus clock, and PCLK bus clocks are driven from
 * SYSCLK. SYSCLK is usually around 13MHz, but may vary based on SYSCLK
 * source or the frequency of the main oscillator. In this mode, the
 * HCLK_PLL can be safely enabled, changed, or disabled.
 *
 * Halt mode:
 * SYSCLK is gated off and the CPU and system clocks are halted.
 * Peripherals based on the 32KHz oscillator clock (ie, RTC, touch,
 * key scanner, etc.) still operate if enabled. In this state, an enabled
 * system event (ie, GPIO state change, RTC match, key press, etc.) will
 * wake the system up back into direct-run mode.
 *
 * DRAM refresh
 * DRAM clocking and refresh are slightly different for systems with DDR
 * DRAM or regular SDRAM devices. If SDRAM is used in the system, the
 * SDRAM will still be accessible in direct-run mode. In DDR based systems,
 * a transition to direct-run mode will stop all DDR accesses (no clocks).
 * Because of this, the code to switch power modes and the code to enter
 * and exit DRAM self-refresh modes must not be executed in DRAM. A small
 * section of IRAM is used instead for this.
 *
 * Suspend is handled with the following logic:
 *  Backup a small area of IRAM used for the suspend code
 *  Copy suspend code to IRAM
 *  Transfer control to code in IRAM
 *  Places DRAMs in self-refresh mode
 *  Enter direct-run mode
 *  Save state of HCLK_PLL PLL
 *  Disable HCLK_PLL PLL
 *  Enter halt mode - CPU and buses will stop
 *  System enters direct-run mode when an enabled event occurs
 *  HCLK PLL state is restored
 *  Run mode is entered
 *  DRAMS are placed back into normal mode
 *  Code execution returns from IRAM
 *  IRAM code are used for suspend is restored
 *  Suspend mode is exited
 */

#include <linux/suspend.h>
#include <linux/io.h>
#include <linux/slab.h>

#include <asm/cacheflush.h>

#include "lpc32xx.h"
#include "common.h"

#define TEMP_IRAM_AREA  IO_ADDRESS(LPC32XX_IRAM_BASE)

/*
 * Both STANDBY and MEM suspend states are handled the same with no
 * loss of CPU or memory state
 */
static int lpc32xx_pm_enter(suspend_state_t state)
{
	int (*lpc32xx_suspend_ptr) (void);
	void *iram_swap_area;

	/* Allocate some space for temporary IRAM storage */
	iram_swap_area = kmemdup((void *)TEMP_IRAM_AREA,
				 lpc32xx_sys_suspend_sz, GFP_KERNEL);
	if (!iram_swap_area)
		return -ENOMEM;

Annotation

Implementation Notes