[RFC PATCH 0/2] Add RISC-V SBI watchdog driver

[Prajwal N]

This series adds a driver for RISC-V SBI watchdog extension.

The SBI watchdog extension exposes watchdog including start,
stop, pat, read and write attributes to the S-mode software.
The kernel driver uses the standard SBI calls to interact and
configure the attributes. The driver integrates with the
kernel watchdog framework (/dev/watchdog) to ease user-space
implementations.

The driver currently subscribes to the Message Signaled
Interrupts (MSI) for watchdog pretimeout events.

The series consists of following changes:

- Patch 1 adds the definition for SBI watchdog extension ID,
  function IDs, and various attributes that are supported by
  the extension

- Patch 2 implements the kernel driver that utilizes standard
  SBI calls to interact and configure the attributes.

This is based on the OpenSBI watchdog extension implementation
patch series available at:
Link: https://lore.kernel.org/opensbi/20261002083040.2533097-1-prajwal.n@oss.qualcomm.com

Steps to test the SBI watchdog extension
1) Compile the kernel along with watchdog kselftest for RISC-V.
2) Compile OpenSBI patch series mentioned earlier to generate fw_dynamic.bin
3) Launch QEMU virt machine with IMSIC support enabled.
   Note: The following command requires a rootfs.cpio packed in Image. It can
   be modified to use rootfs.ext2
   $ qemu-system-riscv64 -M virt,aia=aplic-imsic -m 2G -smp 4 -nographic \
     -bios fw_dynamic.bin -kernel Image -append "root=/dev/vda rw console=ttyS0"
4) On kernel boot-up, the /dev/watchdog entry should be available and the
   kselftest binary (watchdog-test) can be used to test the functionality.
   Following are some sample test cases,
   
   - Dumps all the supported options.
     ./watchdog-test -h

   - Starts the watchdog, configures the timeout to 8s, ping interval to 2s,
     and disables the pretimeout.
     ./watchdog-test -t 8 -p 2 -n 0
     
   - Starts the watchdog, configures the timeout to 8s, ping interval to 9s,
     and disables the pretimeout.
     ./watchdog-test -t 8 -p 9 -n 0

   - Starts the watchdog, configures the timeout to 8s, ping interval to 2s,
     and configures the pretimeout to 6s before the timeout.
     ./watchdog-test -t 8 -p 3 -n 6

Changes in v1:
- Initial RFC submission

Prajwal N (2):
  include: sbi_ecall_interface: Add defines for the RISC-V SBI watchdog
    extension
  drivers/watchdog: Add RISC-V SBI watchdog driver

 arch/riscv/include/asm/sbi.h     |  26 ++
 drivers/watchdog/Kconfig         |   9 +
 drivers/watchdog/Makefile        |   1 +
 drivers/watchdog/riscv_sbi_wdt.c | 406 +++++++++++++++++++++++++++++++
 4 files changed, 442 insertions(+)
 create mode 100644 drivers/watchdog/riscv_sbi_wdt.c

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2.43.0