mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-23 09:19:51 +00:00
![Paul Walmsley](/assets/img/avatar_default.png)
The interface provides device drivers, CPUFreq, and DSPBridge with a means of controlling OMAP power management parameters that are not yet supported by the Linux PM PMQoS interface. Copious documentation is in the patch in Documentation/arm/OMAP/omap_pm and the interface header file, arch/arm/plat-omap/include/mach/omap-pm.h. Thanks to Rajendra Nayak <rnayak@ti.com> for adding CORE (VDD2) OPP support and moving the OPP table initialization earlier in the event that the clock code needs them. Thanks to Tero Kristo <tero.kristo@nokia.com> for fixing the parameter check in omap_pm_set_min_bus_tput(). Jouni signed off on Tero's patch. Signed-off-by: Paul Walmsley <paul@pwsan.com> Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com> Signed-off-by: Rajendra Nayak <rnayak@ti.com> Signed-off-by: Tero Kristo <tero.kristo@nokia.com> Signed-off-by: Jouni Högander <jouni.hogander@nokia.com> Cc: Tony Lindgren <tony@atomide.com> Cc: Igor Stoppa <igor.stoppa@nokia.com> Cc: Richard Woodruff <r-woodruff2@ti.com> Cc: Anand Sawant <sawant@ti.com> Cc: Sakari Poussa <sakari.poussa@nokia.com> Cc: Veeramanikandan Raju <veera@ti.com> Cc: Karthik Dasu <karthik-dp@ti.com>
129 lines
4.9 KiB
Text
129 lines
4.9 KiB
Text
|
|
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)
|