In Linux 4.10-rc8, the implementation to enable the "stop" instruction has the following shortcomings:
a) The code hand-codes the values for ESL, EC, TR, MTL bits of PSSCR and uses only the RL field from the firmware. While this is not incorrect, since the hand-coded values are legitimate, it is not a
very flexible design since the firmware has the capability to communicate these values via the "ibm,cpu-idle-state-psscr" and "ibm,cpu-idle-state-psscr-mask" properties. In case where the firmware provides values for these fields that is different from the hand-coded values, the current code will not work as intended.
b) Due to issue a), the current code assumes that ESL=EC=1 for all the stop states and hence the wakeup from the stop instruction will happen at 0x100, the system-reset vector which also results in GPR state loss. However, the ISA v3.0 allows the ESL=EC=0 behaviour where the corresponding stop-states lose no GPR state and wakes up from the subsequent instruction. The code in 4.10-rc8 doesn't support these light-weight stop modes.
The following commits in the "next" branch of the powerpc-linux git tree (git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git) address these issues. These patches are needed in 17.04 to enable
light-weight stop modes
1) commit 823b7bd5156a93872d9561b3f033dfe5cb80204e, powernv:idle: Add IDLE_STATE_ENTER_SEQ_NORET macro
2)commit dd34c74c97b6c3ed1ac7caec0b46267142659aff, powernv:stop: Rename pnv_arch300_idle_init to pnv_power9_idle_init
3)commit 9e9fc6f00a54f7064dc681ac187be6498d566a4f, cpuidle:powernv: Add helper function to populate powernv idle states
4)commit 09206b600c76f20984e80d99f3b5343c79332a97, powernv: Pass PSSCR value and mask to power9_idle_stop
5)commit b48ff52043f489d594b989b318c120ca340a2e41, Documentation:powerpc: Add device-tree bindings for power-mgt
This bug was fixed in the package linux - 4.10.0-11.13
---------------
linux (4.10.0-11.13) zesty; urgency=low
[ Tim Gardner ]
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