diff options
Diffstat (limited to 'Documentation/arm/OMAP/omap_pm')
| -rw-r--r-- | Documentation/arm/OMAP/omap_pm | 154 |
1 files changed, 0 insertions, 154 deletions
diff --git a/Documentation/arm/OMAP/omap_pm b/Documentation/arm/OMAP/omap_pm deleted file mode 100644 index 4ae915a9f899..000000000000 --- a/Documentation/arm/OMAP/omap_pm +++ /dev/null @@ -1,154 +0,0 @@ - -The OMAP PM interface -===================== - -This document describes the temporary OMAP PM interface. Driver -authors use these functions to communicate minimum latency or -throughput constraints to the kernel power management code. -Over time, the intention is to merge features from the OMAP PM -interface into the Linux PM QoS code. - -Drivers need to express PM parameters which: - -- support the range of power management parameters present in the TI SRF; - -- separate the drivers from the underlying PM parameter - implementation, whether it is the TI SRF or Linux PM QoS or Linux - latency framework or something else; - -- specify PM parameters in terms of fundamental units, such as - latency and throughput, rather than units which are specific to OMAP - or to particular OMAP variants; - -- allow drivers which are shared with other architectures (e.g., - DaVinci) to add these constraints in a way which won't affect non-OMAP - systems, - -- can be implemented immediately with minimal disruption of other - architectures. - - -This document proposes the OMAP PM interface, including the following -five power management functions for driver code: - -1. Set the maximum MPU wakeup latency: - (*pdata->set_max_mpu_wakeup_lat)(struct device *dev, unsigned long t) - -2. Set the maximum device wakeup latency: - (*pdata->set_max_dev_wakeup_lat)(struct device *dev, unsigned long t) - -3. Set the maximum system DMA transfer start latency (CORE pwrdm): - (*pdata->set_max_sdma_lat)(struct device *dev, long t) - -4. Set the minimum bus throughput needed by a device: - (*pdata->set_min_bus_tput)(struct device *dev, u8 agent_id, unsigned long r) - -5. Return the number of times the device has lost context - (*pdata->get_dev_context_loss_count)(struct device *dev) - - -Further documentation for all OMAP PM interface functions can be -found in arch/arm/plat-omap/include/mach/omap-pm.h. - - -The OMAP PM layer is intended to be temporary ---------------------------------------------- - -The intention is that eventually the Linux PM QoS layer should support -the range of power management features present in OMAP3. As this -happens, existing drivers using the OMAP PM interface can be modified -to use the Linux PM QoS code; and the OMAP PM interface can disappear. - - -Driver usage of the OMAP PM functions -------------------------------------- - -As the 'pdata' in the above examples indicates, these functions are -exposed to drivers through function pointers in driver .platform_data -structures. The function pointers are initialized by the board-*.c -files to point to the corresponding OMAP PM functions: -.set_max_dev_wakeup_lat will point to -omap_pm_set_max_dev_wakeup_lat(), etc. Other architectures which do -not support these functions should leave these function pointers set -to NULL. Drivers should use the following idiom: - - if (pdata->set_max_dev_wakeup_lat) - (*pdata->set_max_dev_wakeup_lat)(dev, t); - -The most common usage of these functions will probably be to specify -the maximum time from when an interrupt occurs, to when the device -becomes accessible. To accomplish this, driver writers should use the -set_max_mpu_wakeup_lat() function to constrain the MPU wakeup -latency, and the set_max_dev_wakeup_lat() function to constrain the -device wakeup latency (from clk_enable() to accessibility). For -example, - - /* Limit MPU wakeup latency */ - if (pdata->set_max_mpu_wakeup_lat) - (*pdata->set_max_mpu_wakeup_lat)(dev, tc); - - /* Limit device powerdomain wakeup latency */ - if (pdata->set_max_dev_wakeup_lat) - (*pdata->set_max_dev_wakeup_lat)(dev, td); - - /* total wakeup latency in this example: (tc + td) */ - -The PM parameters can be overwritten by calling the function again -with the new value. The settings can be removed by calling the -function with a t argument of -1 (except in the case of -set_max_bus_tput(), which should be called with an r argument of 0). - -The fifth function above, omap_pm_get_dev_context_loss_count(), -is intended as an optimization to allow drivers to determine whether the -device has lost its internal context. If context has been lost, the -driver must restore its internal context before proceeding. - - -Other specialized interface functions -------------------------------------- - -The five functions listed above are intended to be usable by any -device driver. DSPBridge and CPUFreq have a few special requirements. -DSPBridge expresses target DSP performance levels in terms of OPP IDs. -CPUFreq expresses target MPU performance levels in terms of MPU -frequency. The OMAP PM interface contains functions for these -specialized cases to convert that input information (OPPs/MPU -frequency) into the form that the underlying power management -implementation needs: - -6. (*pdata->dsp_get_opp_table)(void) - -7. (*pdata->dsp_set_min_opp)(u8 opp_id) - -8. (*pdata->dsp_get_opp)(void) - -9. (*pdata->cpu_get_freq_table)(void) - -10. (*pdata->cpu_set_freq)(unsigned long f) - -11. (*pdata->cpu_get_freq)(void) - -Customizing OPP for platform -============================ -Defining CONFIG_PM should enable OPP layer for the silicon -and the registration of OPP table should take place automatically. -However, in special cases, the default OPP table may need to be -tweaked, for e.g.: - * enable default OPPs which are disabled by default, but which - could be enabled on a platform - * Disable an unsupported OPP on the platform - * Define and add a custom opp table entry -in these cases, the board file needs to do additional steps as follows: -arch/arm/mach-omapx/board-xyz.c - #include "pm.h" - .... - static void __init omap_xyz_init_irq(void) - { - .... - /* Initialize the default table */ - omapx_opp_init(); - /* Do customization to the defaults */ - .... - } -NOTE: omapx_opp_init will be omap3_opp_init or as required -based on the omap family. |