1 S3C24XX Suspend Support 2 ======================= 3 4 5Introduction 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 14Requirements 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 27Resuming 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 40Machine Support 41--------------- 42 43 The machine specific functions must call the s3c2410_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(s3c2410_pm_init) 48 49 A board can do its own setup before calling s3c2410_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 63static irqreturn_t button_irq(int irq, void *pw) 64{ 65 return IRQ_HANDLED; 66} 67 68statuc 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 s3c2410_pm_init(); 78} 79 80 81Debugging 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 101Configuration 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 dependant 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 133Document Author 134--------------- 135 136Ben Dooks, (c) 2004 Simtec Electronics 137