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author | Russell King <rmk+kernel@arm.linux.org.uk> | 2009-09-24 21:22:33 +0100 |
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committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2009-09-24 21:22:33 +0100 |
commit | baea7b946f00a291b166ccae7fcfed6c01530cc6 (patch) | |
tree | 4aa275fbdbec9c7b9b4629e8bee2bbecd3c6a6af /Documentation/arm/OMAP/omap_pm | |
parent | ae19ffbadc1b2100285a5b5b3d0a4e0a11390904 (diff) | |
parent | 94e0fb086fc5663c38bbc0fe86d698be8314f82f (diff) | |
download | talos-obmc-linux-baea7b946f00a291b166ccae7fcfed6c01530cc6.tar.gz talos-obmc-linux-baea7b946f00a291b166ccae7fcfed6c01530cc6.zip |
Merge branch 'origin' into for-linus
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Diffstat (limited to 'Documentation/arm/OMAP/omap_pm')
-rw-r--r-- | Documentation/arm/OMAP/omap_pm | 129 |
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diff --git a/Documentation/arm/OMAP/omap_pm b/Documentation/arm/OMAP/omap_pm new file mode 100644 index 000000000000..5389440aade3 --- /dev/null +++ b/Documentation/arm/OMAP/omap_pm @@ -0,0 +1,129 @@ + +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 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) |