1 2The OMAP PM interface 3===================== 4 5This document describes the temporary OMAP PM interface. Driver 6authors use these functions to communicate minimum latency or 7throughput constraints to the kernel power management code. 8Over time, the intention is to merge features from the OMAP PM 9interface 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 parameter 16 implementation, whether it is the TI SRF or Linux PM QoS or Linux 17 latency framework or something else; 18 19- specify PM parameters in terms of fundamental units, such as 20 latency and throughput, rather than units which are specific to OMAP 21 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-OMAP 25 systems, 26 27- can be implemented immediately with minimal disruption of other 28 architectures. 29 30 31This document proposes the OMAP PM interface, including the following 32five power management functions for driver code: 33 341. Set the maximum MPU wakeup latency: 35 (*pdata->set_max_mpu_wakeup_lat)(struct device *dev, unsigned long t) 36 372. Set the maximum device wakeup latency: 38 (*pdata->set_max_dev_wakeup_lat)(struct device *dev, unsigned long t) 39 403. Set the maximum system DMA transfer start latency (CORE pwrdm): 41 (*pdata->set_max_sdma_lat)(struct device *dev, long t) 42 434. Set the minimum bus throughput needed by a device: 44 (*pdata->set_min_bus_tput)(struct device *dev, u8 agent_id, unsigned long r) 45 465. Return the number of times the device has lost context 47 (*pdata->get_dev_context_loss_count)(struct device *dev) 48 49 50Further documentation for all OMAP PM interface functions can be 51found in arch/arm/plat-omap/include/mach/omap-pm.h. 52 53 54The OMAP PM layer is intended to be temporary 55--------------------------------------------- 56 57The intention is that eventually the Linux PM QoS layer should support 58the range of power management features present in OMAP3. As this 59happens, existing drivers using the OMAP PM interface can be modified 60to use the Linux PM QoS code; and the OMAP PM interface can disappear. 61 62 63Driver usage of the OMAP PM functions 64------------------------------------- 65 66As the 'pdata' in the above examples indicates, these functions are 67exposed to drivers through function pointers in driver .platform_data 68structures. The function pointers are initialized by the board-*.c 69files to point to the corresponding OMAP PM functions: 70.set_max_dev_wakeup_lat will point to 71omap_pm_set_max_dev_wakeup_lat(), etc. Other architectures which do 72not support these functions should leave these function pointers set 73to NULL. Drivers should use the following idiom: 74 75 if (pdata->set_max_dev_wakeup_lat) 76 (*pdata->set_max_dev_wakeup_lat)(dev, t); 77 78The most common usage of these functions will probably be to specify 79the maximum time from when an interrupt occurs, to when the device 80becomes accessible. To accomplish this, driver writers should use the 81set_max_mpu_wakeup_lat() function to to constrain the MPU wakeup 82latency, and the set_max_dev_wakeup_lat() function to constrain the 83device wakeup latency (from clk_enable() to accessibility). For 84example, 85 86 /* Limit MPU wakeup latency */ 87 if (pdata->set_max_mpu_wakeup_lat) 88 (*pdata->set_max_mpu_wakeup_lat)(dev, tc); 89 90 /* Limit device powerdomain wakeup latency */ 91 if (pdata->set_max_dev_wakeup_lat) 92 (*pdata->set_max_dev_wakeup_lat)(dev, td); 93 94 /* total wakeup latency in this example: (tc + td) */ 95 96The PM parameters can be overwritten by calling the function again 97with the new value. The settings can be removed by calling the 98function with a t argument of -1 (except in the case of 99set_max_bus_tput(), which should be called with an r argument of 0). 100 101The fifth function above, omap_pm_get_dev_context_loss_count(), 102is intended as an optimization to allow drivers to determine whether the 103device has lost its internal context. If context has been lost, the 104driver must restore its internal context before proceeding. 105 106 107Other specialized interface functions 108------------------------------------- 109 110The five functions listed above are intended to be usable by any 111device driver. DSPBridge and CPUFreq have a few special requirements. 112DSPBridge expresses target DSP performance levels in terms of OPP IDs. 113CPUFreq expresses target MPU performance levels in terms of MPU 114frequency. The OMAP PM interface contains functions for these 115specialized cases to convert that input information (OPPs/MPU 116frequency) into the form that the underlying power management 117implementation needs: 118 1196. (*pdata->dsp_get_opp_table)(void) 120 1217. (*pdata->dsp_set_min_opp)(u8 opp_id) 122 1238. (*pdata->dsp_get_opp)(void) 124 1259. (*pdata->cpu_get_freq_table)(void) 126 12710. (*pdata->cpu_set_freq)(unsigned long f) 128 12911. (*pdata->cpu_get_freq)(void) 130