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1=====================2The OMAP PM interface3=====================4 5This document describes the temporary OMAP PM interface. Driver6authors use these functions to communicate minimum latency or7throughput constraints to the kernel power management code.8Over time, the intention is to merge features from the OMAP PM9interface into the Linux PM QoS code.10 11Drivers need to express PM parameters which:12 13- support the range of power management parameters present in the TI SRF;14 15- separate the drivers from the underlying PM parameter16 implementation, whether it is the TI SRF or Linux PM QoS or Linux17 latency framework or something else;18 19- specify PM parameters in terms of fundamental units, such as20 latency and throughput, rather than units which are specific to OMAP21 or to particular OMAP variants;22 23- allow drivers which are shared with other architectures (e.g.,24 DaVinci) to add these constraints in a way which won't affect non-OMAP25 systems,26 27- can be implemented immediately with minimal disruption of other28 architectures.29 30 31This document proposes the OMAP PM interface, including the following32five power management functions for driver code:33 341. Set the maximum MPU wakeup latency::35 36 (*pdata->set_max_mpu_wakeup_lat)(struct device *dev, unsigned long t)37 382. Set the maximum device wakeup latency::39 40 (*pdata->set_max_dev_wakeup_lat)(struct device *dev, unsigned long t)41 423. Set the maximum system DMA transfer start latency (CORE pwrdm)::43 44 (*pdata->set_max_sdma_lat)(struct device *dev, long t)45 464. Set the minimum bus throughput needed by a device::47 48 (*pdata->set_min_bus_tput)(struct device *dev, u8 agent_id, unsigned long r)49 505. Return the number of times the device has lost context::51 52 (*pdata->get_dev_context_loss_count)(struct device *dev)53 54 55Further documentation for all OMAP PM interface functions can be56found in arch/arm/plat-omap/include/mach/omap-pm.h.57 58 59The OMAP PM layer is intended to be temporary60---------------------------------------------61 62The intention is that eventually the Linux PM QoS layer should support63the range of power management features present in OMAP3. As this64happens, existing drivers using the OMAP PM interface can be modified65to use the Linux PM QoS code; and the OMAP PM interface can disappear.66 67 68Driver usage of the OMAP PM functions69-------------------------------------70 71As the 'pdata' in the above examples indicates, these functions are72exposed to drivers through function pointers in driver .platform_data73structures. The function pointers are initialized by the `board-*.c`74files to point to the corresponding OMAP PM functions:75 76- set_max_dev_wakeup_lat will point to77 omap_pm_set_max_dev_wakeup_lat(), etc. Other architectures which do78 not support these functions should leave these function pointers set79 to NULL. Drivers should use the following idiom::80 81 if (pdata->set_max_dev_wakeup_lat)82 (*pdata->set_max_dev_wakeup_lat)(dev, t);83 84The most common usage of these functions will probably be to specify85the maximum time from when an interrupt occurs, to when the device86becomes accessible. To accomplish this, driver writers should use the87set_max_mpu_wakeup_lat() function to constrain the MPU wakeup88latency, and the set_max_dev_wakeup_lat() function to constrain the89device wakeup latency (from clk_enable() to accessibility). For90example::91 92 /* Limit MPU wakeup latency */93 if (pdata->set_max_mpu_wakeup_lat)94 (*pdata->set_max_mpu_wakeup_lat)(dev, tc);95 96 /* Limit device powerdomain wakeup latency */97 if (pdata->set_max_dev_wakeup_lat)98 (*pdata->set_max_dev_wakeup_lat)(dev, td);99 100 /* total wakeup latency in this example: (tc + td) */101 102The PM parameters can be overwritten by calling the function again103with the new value. The settings can be removed by calling the104function with a t argument of -1 (except in the case of105set_max_bus_tput(), which should be called with an r argument of 0).106 107The fifth function above, omap_pm_get_dev_context_loss_count(),108is intended as an optimization to allow drivers to determine whether the109device has lost its internal context. If context has been lost, the110driver must restore its internal context before proceeding.111 112 113Other specialized interface functions114-------------------------------------115 116The five functions listed above are intended to be usable by any117device driver. DSPBridge and CPUFreq have a few special requirements.118DSPBridge expresses target DSP performance levels in terms of OPP IDs.119CPUFreq expresses target MPU performance levels in terms of MPU120frequency. The OMAP PM interface contains functions for these121specialized cases to convert that input information (OPPs/MPU122frequency) into the form that the underlying power management123implementation needs:124 1256. `(*pdata->dsp_get_opp_table)(void)`126 1277. `(*pdata->dsp_set_min_opp)(u8 opp_id)`128 1298. `(*pdata->dsp_get_opp)(void)`130 1319. `(*pdata->cpu_get_freq_table)(void)`132 13310. `(*pdata->cpu_set_freq)(unsigned long f)`134 13511. `(*pdata->cpu_get_freq)(void)`136 137Customizing OPP for platform138============================139Defining CONFIG_PM should enable OPP layer for the silicon140and the registration of OPP table should take place automatically.141However, in special cases, the default OPP table may need to be142tweaked, for e.g.:143 144 * enable default OPPs which are disabled by default, but which145 could be enabled on a platform146 * Disable an unsupported OPP on the platform147 * Define and add a custom opp table entry148 in these cases, the board file needs to do additional steps as follows:149 150arch/arm/mach-omapx/board-xyz.c::151 152 #include "pm.h"153 ....154 static void __init omap_xyz_init_irq(void)155 {156 ....157 /* Initialize the default table */158 omapx_opp_init();159 /* Do customization to the defaults */160 ....161 }162 163NOTE:164 omapx_opp_init will be omap3_opp_init or as required165 based on the omap family.166