[0/4] Fix Google Tensor GS101 CPU hotplug support

Message

Peter Griffin Dec. 13, 2024, 4:44 p.m. UTC

Hi folks,

As part of an effort to make suspend to RAM functional upstream on
Pixel 6 I noticed that CPU hotplug leads to a system hang.

After debugging and comparing with downstream drivers it became clear
that some extra register writes are required to make CPU hotplug
functional on these older devices which use the el3mon firmware.

This series adds support for programming the CPU_INFORM register hint
required by the firmware and also adds support for the pmu-intr-gen
register region. This is achieved using cpuhp_setup_state() to setup
a cpu hotplug state. This is similar to soc/xilinx/xlnx_event_manager.c
and soc/fsl/qbman/bman_portal.c drivers.

With these changes CPU hotplug is now functional :)

It can be tested with commands such as

echo 0 > /sys/devices/system/cpu/cpu6/online
echo 1 > /sys/devices/system/cpu/cpu6/online
[   15.880597][    T0] Detected PIPT I-cache on CPU6
[   15.880638][    T0] GICv3: CPU6: found redistributor 600 region 0:0x0000000010500000
[   15.880685][    T0] CPU6: Booted secondary processor 0x0000000600 [0x411fd440]

This would (prior to this series) hang the system.

Note 1: It is highly likely that similar changes are required for other
Exynos based SoCs using el3mon. For anyone following along who is
accustomed to looking at downstream Exynos based drivers this replaces
register writes defined in 

drivers/soc/<google|samsung>/cal-if/<socname>/flexpmu_cal_cpu_<socname>.h

Which are used by files in the cal-if folder and exynos-cpupm.c driver.

For the moment I've used the GS101 CPU inform register offsets directly
but these can be moved to driver data once we've established other SoCs
benefit from this.

Note 2: To ensure older DTs which don't define pmu-intr-gen register
region still work. The driver only issues a warning if the registers
can't be mapped, and the behaviour remains the same as today (system
boots, but CPU hotplug will not be functional).

Signed-off-by: Peter Griffin <[e-mail]>
---
Peter Griffin (4):
      dt-bindings: soc: samsung: exynos-pmu: gs101: add pmu-intr-gen reg region
      dt-bindings: mfd: syscon: allow two reg regions for gs101-pmu
      arm64: dts: exynos: gs101: add pmu-intr-gen regs to the PMU node
      soc: samsung: exynos-pmu: enable CPU hotplug support for gs101

 .../devicetree/bindings/mfd/syscon-common.yaml     | 10 +++
 .../bindings/soc/samsung/exynos-pmu.yaml           | 29 ++++++++-
 arch/arm64/boot/dts/exynos/google/gs101.dtsi       |  4 +-
 drivers/soc/samsung/exynos-pmu.c                   | 73 +++++++++++++++++++++-
 drivers/soc/samsung/exynos-pmu.h                   |  1 +
 include/linux/soc/samsung/exynos-regs-pmu.h        | 11 ++++
 6 files changed, 125 insertions(+), 3 deletions(-)
---
base-commit: ed9a4ad6e5bd3a443e81446476718abebee47e82
change-id: 20241213-contrib-pg-cpu-hotplug-suspend2ram-fixes-v1-1f7ad4c45901

Best regards,