1 =====================
2 The OMAP PM interface
3 =====================
4
5 This document describes the temporary OMAP PM
6 authors use these functions to communicate min
7 throughput constraints to the kernel power man
8 Over time, the intention is to merge features
9 interface into the Linux PM QoS code.
10
11 Drivers need to express PM parameters which:
12
13 - support the range of power management parame
14
15 - separate the drivers from the underlying PM
16 implementation, whether it is the TI SRF or
17 latency framework or something else;
18
19 - specify PM parameters in terms of fundamenta
20 latency and throughput, rather than units wh
21 or to particular OMAP variants;
22
23 - allow drivers which are shared with other ar
24 DaVinci) to add these constraints in a way w
25 systems,
26
27 - can be implemented immediately with minimal
28 architectures.
29
30
31 This document proposes the OMAP PM interface,
32 five power management functions for driver cod
33
34 1. Set the maximum MPU wakeup latency::
35
36 (*pdata->set_max_mpu_wakeup_lat)(struct dev
37
38 2. Set the maximum device wakeup latency::
39
40 (*pdata->set_max_dev_wakeup_lat)(struct dev
41
42 3. Set the maximum system DMA transfer start l
43
44 (*pdata->set_max_sdma_lat)(struct device *d
45
46 4. Set the minimum bus throughput needed by a
47
48 (*pdata->set_min_bus_tput)(struct device *d
49
50 5. Return the number of times the device has l
51
52 (*pdata->get_dev_context_loss_count)(struct
53
54
55 Further documentation for all OMAP PM interfac
56 found in arch/arm/plat-omap/include/mach/omap-
57
58
59 The OMAP PM layer is intended to be temporary
60 ---------------------------------------------
61
62 The intention is that eventually the Linux PM
63 the range of power management features present
64 happens, existing drivers using the OMAP PM in
65 to use the Linux PM QoS code; and the OMAP PM
66
67
68 Driver usage of the OMAP PM functions
69 -------------------------------------
70
71 As the 'pdata' in the above examples indicates
72 exposed to drivers through function pointers i
73 structures. The function pointers are initial
74 files to point to the corresponding OMAP PM fu
75
76 - set_max_dev_wakeup_lat will point to
77 omap_pm_set_max_dev_wakeup_lat(), etc. Othe
78 not support these functions should leave the
79 to NULL. Drivers should use the following i
80
81 if (pdata->set_max_dev_wakeup_lat)
82 (*pdata->set_max_dev_wakeup_lat)(d
83
84 The most common usage of these functions will
85 the maximum time from when an interrupt occurs
86 becomes accessible. To accomplish this, drive
87 set_max_mpu_wakeup_lat() function to constrain
88 latency, and the set_max_dev_wakeup_lat() func
89 device wakeup latency (from clk_enable() to ac
90 example::
91
92 /* Limit MPU wakeup latency */
93 if (pdata->set_max_mpu_wakeup_lat)
94 (*pdata->set_max_mpu_wakeup_lat)(d
95
96 /* Limit device powerdomain wakeup lat
97 if (pdata->set_max_dev_wakeup_lat)
98 (*pdata->set_max_dev_wakeup_lat)(d
99
100 /* total wakeup latency in this exampl
101
102 The PM parameters can be overwritten by callin
103 with the new value. The settings can be remov
104 function with a t argument of -1 (except in th
105 set_max_bus_tput(), which should be called wit
106
107 The fifth function above, omap_pm_get_dev_cont
108 is intended as an optimization to allow driver
109 device has lost its internal context. If cont
110 driver must restore its internal context befor
111
112
113 Other specialized interface functions
114 -------------------------------------
115
116 The five functions listed above are intended t
117 device driver. DSPBridge and CPUFreq have a f
118 DSPBridge expresses target DSP performance lev
119 CPUFreq expresses target MPU performance level
120 frequency. The OMAP PM interface contains fun
121 specialized cases to convert that input inform
122 frequency) into the form that the underlying p
123 implementation needs:
124
125 6. `(*pdata->dsp_get_opp_table)(void)`
126
127 7. `(*pdata->dsp_set_min_opp)(u8 opp_id)`
128
129 8. `(*pdata->dsp_get_opp)(void)`
130
131 9. `(*pdata->cpu_get_freq_table)(void)`
132
133 10. `(*pdata->cpu_set_freq)(unsigned long f)`
134
135 11. `(*pdata->cpu_get_freq)(void)`
136
137 Customizing OPP for platform
138 ============================
139 Defining CONFIG_PM should enable OPP layer for
140 and the registration of OPP table should take
141 However, in special cases, the default OPP tab
142 tweaked, for e.g.:
143
144 * enable default OPPs which are disabled by d
145 could be enabled on a platform
146 * Disable an unsupported OPP on the platform
147 * Define and add a custom opp table entry
148 in these cases, the board file needs to do
149
150 arch/arm/mach-omapx/board-xyz.c::
151
152 #include "pm.h"
153 ....
154 static void __init omap_xyz_init_irq(v
155 {
156 ....
157 /* Initialize the default tabl
158 omapx_opp_init();
159 /* Do customization to the def
160 ....
161 }
162
163 NOTE:
164 omapx_opp_init will be omap3_opp_init or as
165 based on the omap family.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.