About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / arm / Samsung-S3C24XX / Suspend.txt




Custom Search

Based on kernel version 3.15.4. Page generated on 2014-07-07 08:59 EST.

1				S3C24XX Suspend Support
2				=======================
3	
4	
5	Introduction
6	------------
7	
8	  The S3C24XX supports a low-power suspend mode, where the SDRAM is kept
9	  in Self-Refresh mode, and all but the essential peripheral blocks are
10	  powered down. For more information on how this works, please look
11	  at the relevant CPU datasheet from Samsung.
12	
13	
14	Requirements
15	------------
16	
17	  1) A bootloader that can support the necessary resume operation
18	
19	  2) Support for at least 1 source for resume
20	
21	  3) CONFIG_PM enabled in the kernel
22	
23	  4) Any peripherals that are going to be powered down at the same
24	     time require suspend/resume support.
25	
26	
27	Resuming
28	--------
29	
30	  The S3C2410 user manual defines the process of sending the CPU to
31	  sleep and how it resumes. The default behaviour of the Linux code
32	  is to set the GSTATUS3 register to the physical address of the
33	  code to resume Linux operation.
34	
35	  GSTATUS4 is currently left alone by the sleep code, and is free to
36	  use for any other purposes (for example, the EB2410ITX uses this to
37	  save memory configuration in).
38	
39	
40	Machine Support
41	---------------
42	
43	  The machine specific functions must call the s3c_pm_init() function
44	  to say that its bootloader is capable of resuming. This can be as
45	  simple as adding the following to the machine's definition:
46	
47	  INITMACHINE(s3c_pm_init)
48	
49	  A board can do its own setup before calling s3c_pm_init, if it
50	  needs to setup anything else for power management support.
51	
52	  There is currently no support for over-riding the default method of
53	  saving the resume address, if your board requires it, then contact
54	  the maintainer and discuss what is required.
55	
56	  Note, the original method of adding an late_initcall() is wrong,
57	  and will end up initialising all compiled machines' pm init!
58	
59	  The following is an example of code used for testing wakeup from
60	  an falling edge on IRQ_EINT0:
61	
62	
63	static irqreturn_t button_irq(int irq, void *pw)
64	{
65		return IRQ_HANDLED;
66	}
67	
68	statuc void __init machine_init(void)
69	{
70		...
71	
72		request_irq(IRQ_EINT0, button_irq, IRQF_TRIGGER_FALLING,
73			   "button-irq-eint0", NULL);
74	
75		enable_irq_wake(IRQ_EINT0);
76	
77		s3c_pm_init();
78	}
79	
80	
81	Debugging
82	---------
83	
84	  There are several important things to remember when using PM suspend:
85	
86	  1) The uart drivers will disable the clocks to the UART blocks when
87	     suspending, which means that use of printascii() or similar direct
88	     access to the UARTs will cause the debug to stop.
89	
90	  2) Whilst the pm code itself will attempt to re-enable the UART clocks,
91	     care should be taken that any external clock sources that the UARTs
92	     rely on are still enabled at that point.
93	
94	  3) If any debugging is placed in the resume path, then it must have the
95	     relevant clocks and peripherals setup before use (ie, bootloader).
96	
97	     For example, if you transmit a character from the UART, the baud
98	     rate and uart controls must be setup beforehand.
99	
100	
101	Configuration
102	-------------
103	
104	  The S3C2410 specific configuration in `System Type` defines various
105	  aspects of how the S3C2410 suspend and resume support is configured
106	
107	  `S3C2410 PM Suspend debug`
108	
109	    This option prints messages to the serial console before and after
110	    the actual suspend, giving detailed information on what is
111	    happening
112	
113	
114	  `S3C2410 PM Suspend Memory CRC`
115	
116	    Allows the entire memory to be checksummed before and after the
117	    suspend to see if there has been any corruption of the contents.
118	
119	    Note, the time to calculate the CRC is dependent on the CPU speed
120	    and the size of memory. For an 64Mbyte RAM area on an 200MHz
121	    S3C2410, this can take approximately 4 seconds to complete.
122	
123	    This support requires the CRC32 function to be enabled.
124	
125	
126	  `S3C2410 PM Suspend CRC Chunksize (KiB)`
127	
128	    Defines the size of memory each CRC chunk covers. A smaller value
129	    will mean that the CRC data block will take more memory, but will
130	    identify any faults with better precision
131	
132	
133	Document Author
134	---------------
135	
136	Ben Dooks, Copyright 2004 Simtec Electronics
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.