linux-kernel - [PATCH RFC 0/2] Implement vendor resets for PSCI SYSTEM

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Message-ID: <20231030-arm-psci-system_reset2-vendor-reboots-v1-0-dcdd63352ad1@quicinc.com>
Date:   Mon, 30 Oct 2023 14:31:32 -0700
From:   Elliot Berman <quic_eberman@...cinc.com>
To:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Mark Rutland <mark.rutland@....com>
CC:     Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>,
        Melody Olvera <quic_molvera@...cinc.com>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Florian Fainelli <florian.fainelli@...adcom.com>,
        Elliot Berman <quic_eberman@...cinc.com>
Subject: [PATCH RFC 0/2] Implement vendor resets for PSCI SYSTEM_RESET2

The PSCI SYSTEM_RESET2 call allows vendor firmware to define additional
reset types which could be mapped to the reboot argument.

Setting up reboot on Qualcomm devices can be inconsistent from chipset
to chipset.  Generally, there is a PMIC register that gets written to
decide the reboot type. There is also sometimes a cookie that can be
written to indicate that the bootloader should behave differently than a
regular boot. These knobs evolve over product generations and require 
more drivers. Qualcomm firmwares are beginning to expose vendor
SYSTEM_RESET2 types to simplify driver requirements from Linux.

Add support in PSCI to statically wire reboot mode commands from
userspace to a vendor reset and cookie value using the device tree. The
DT bindings are similar to reboot mode framework except that 2
integers are accepted (the type and cookie). Also, reboot mode framework
is intended to program, but not reboot, the host. PSCI SYSTEM_RESET2
does both. I've not added support for reading ACPI tables since I don't
have any device which provides them + firmware that supports vendor
SYSTEM_RESET2 types.

Previous discussions around SYSTEM_RESET2:
- https://lore.kernel.org/lkml/20230724223057.1208122-2-quic_eberman@quicinc.com/T/
- https://lore.kernel.org/all/4a679542-b48d-7e11-f33a-63535a5c68cb@quicinc.com/

This RFC approach differs from the one sent in July by:
- Not using the reboot mode framework
- Added support to control both reset type and cookie
- Implicitly dropped "normal" reboot command, which is always just
  SYSTEM_RESET anyway.

Signed-off-by: Elliot Berman <quic_eberman@...cinc.com>
---
Elliot Berman (2):
      dt-bindings: arm: Document reboot mode magic
      firmware: psci: Read and use vendor reset types

 Documentation/devicetree/bindings/arm/psci.yaml | 13 ++++
 drivers/firmware/psci/psci.c                    | 87 ++++++++++++++++++++++++-
 2 files changed, 99 insertions(+), 1 deletion(-)
---
base-commit: 22e877699642285c47f5d7d83b2d59815c29ebe8
change-id: 20231016-arm-psci-system_reset2-vendor-reboots-cc3ad456c070

Best regards,
-- 
Elliot Berman <quic_eberman@...cinc.com>