docs/design_documents/psci_osi_mode.rst

1 PSCI OS-initiated mode
36 Platform-coordinated mode is the default mode of power state coordination, and
37 is currently the only supported mode in TF-A.
39 In platform-coordinated mode, the platform is responsible for coordinating power
46 OS-initiated mode is optional.
48 In OS-initiated mode, the calling OS is responsible for coordinating power
55 There are two reasons why OS-initiated mode might be a more suitable option than
56 platform-coordinated mode for a platform.
61 In platform-coordinated mode, each core independently selects their own local
65 In OS-initiated mode, the OS has knowledge of the next wakeup event for each
75 In platform-coordinated mode, the OS doesn't have visibility when the last core
80 platform-coordinated mode when it should be using OS-initiated mode instead.
82 In OS-initiated mode, the OS can perform last man activity if it selects a
92   * For their ARM32 platforms, they're using OS-initiated mode implemented in
95     mode in TF-A.
99   * For their mobile platforms, they're using OS-initiated mode implemented in
101   * For their Chrome OS platforms, they're using platform-coordinated mode in
106   * They're using platform-coordinated mode in TF-A with custom driver logic to
109 Both Qualcomm and Google would like to be able to use OS-initiated mode in TF-A
138 * OS-initiated mode, bit[0]
140   * A value of 0 indicates OS-initiated mode is not supported.
141   * A value of 1 indicates OS-initiated mode is supported.
154    :param mode: 0 indicates platform-coordinated mode, 1 indicates OS-initiated
155        mode.
157    :retval NOT_SUPPORTED: if OS-initiated mode is not supported.
158    :retval INVALID_PARAMETERS: if the requested mode is not a valid value (0 or
171 * None of the cores has called CPU_SUSPEND since the last change of mode or
196    :retval INVALID_PARAMETERS: in OS-initiated mode, this error is returned when
201    :retval DENIED: only in OS-initiated mode; this error is returned when a
206 In platform-coordinated mode, the PSCI implementation coordinates requests from
209 In OS-initiated mode, the calling OS is making an explicit request for a
237   * In OS-initiated mode, the state ID encoding must allow expressing the
246 Races in OS-initiated mode
249 In OS-initiated mode, there are race windows where the OS's view and
277 coordination mode for suspend is platform-coordinated or OS-initiated. If all
280 In OS-initiated mode, if a subset of the cores in a topology node has called
289 Current implementation of platform-coordinated mode
293 mode in TF-A.
322 Proposed implementation of OS-initiated mode
325 To add support for OS-initiated mode, the following changes are proposed:
328   optional support for PSCI OS-initiated mode. This build option defaults to 0.
336   OS-initiated mode for CPU_SUSPEND.
376 .. image:: ../resources/diagrams/psci-osi-mode.png
387 The proposed patches add a new CPU Suspend in OSI mode test suite to TF-A Tests.
675 * Platform-coordinated mode
684 * OS-initiated mode
709 .. image:: ../resources/diagrams/psci-pc-mode-vs-osi-mode.png
711 OS-initiated mode was able to scale better than platform-coordinated mode for
713 idle state) in OS-initiated mode for multiple CPUs were much closer to the
714 results for a single CPU than in platform-coordinated mode.