linux-kernel - [PATCH V3 0/2] SCM: Add support for wait-queue aware firmware

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Date:   Tue, 18 Oct 2022 15:16:44 +0530
From:   Sibi Sankar <quic_sibis@...cinc.com>
To:     <andersson@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <robh+dt@...nel.org>
CC:     <agross@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <konrad.dybcio@...ainline.org>, <robimarko@...il.com>,
        <quic_gurus@...cinc.com>, <quic_rjendra@...cinc.com>,
        Sibi Sankar <quic_sibis@...cinc.com>
Subject: [PATCH V3 0/2] SCM: Add support for wait-queue aware firmware

This patch series enables the QCOM SCM driver to support firmware (FW) versions
that expect the high-level OS (HLOS) to be tolerant of SCM call requests not
being processed right away and, instead, being placed on a wait-queue in FW and
processed accordingly.

The problem this feature is fixing is as follows. In a scenario where there is
a VM in addition to HLOS (and an underlying hypervisor):

1. HLOS makes an SMC call on core 5
2. The hypervisor scheduling interrupt interrupts this SMC call.
3. The hypervisor schedules the VM on core 5.
4. The VM makes an SMC call on core 5.
5. The SMC call is non-interruptibly stuck on FW spinlock on core 5.
6. HLOS cannot reschedule since core 5 is not responding to Reschedule IPIs.
7. Watchdog timer expires waiting for core 5.

This problem is solved by FW returning a new return code SCM_WAITQ_SLEEP to
HLOS right away when it is overwhelmed by the VM's SMC call. HLOS then places
the call on a wait-queue and wakes it up when it receives an interrupt that
signifies "all-clear".

There are two new SMC calls also being defined in this design that, together
with one new return code, form the handshake protocol between Linux and FW.

This design is also backwards-compatible with existing firmware versions that
do not support this feature.

v3:
- Drop allow-multi-call property since HLOS doesn't completely support it
  yet.
- Fixup irq handling so as not to affect SoCs without the interrupt.
- Fix warnings reported by kernel test-bot.

v2:
- Changes made to patches 4 and 5 are listed therein.
- Rebased dt-bindings on top of the YAML conversion patch [1].

Older version of the series:
[v2] https://patchwork.kernel.org/project/linux-arm-msm/cover/1661898311-30126-1-git-send-email-quic_gurus@quicinc.com/
[v1] https://patchwork.kernel.org/project/linux-arm-msm/cover/1656359076-13018-1-git-send-email-quic_gurus@quicinc.com/

Guru Das Srinagesh (2):
  dt-bindings: firmware: qcom-scm: Add optional interrupt
  firmware: qcom: scm: Add wait-queue handling logic

 .../devicetree/bindings/firmware/qcom,scm.yaml     |   5 +
 drivers/firmware/qcom_scm-smc.c                    | 108 +++++++++++++++++--
 drivers/firmware/qcom_scm.c                        | 120 ++++++++++++++++++++-
 drivers/firmware/qcom_scm.h                        |  10 ++
 4 files changed, 234 insertions(+), 9 deletions(-)

-- 
2.7.4