[RyanTheTide]

The remaining macsmc-hwmon board fallback moves into DT. J516s, J516c and J514c now describe their SoC die keys in their board files; J516s also describes its mTPL thermal pressure key. The driver consumes that data and removes macsmc_hwmon_boards[], board_keys and soc_die_keys.

Depends on #639. This branch includes its three commits unchanged, followed by three new commits for the binding, board data and driver. Merge #639 first. The fan implementation from #639 and the fan curves discussed in #579 are unchanged.

apple,soc-die-keys is an ordered string list on the hwmon node. Its channels follow the existing temperature children, retaining the old labels, key validation, hottest-sensor zone and failed-read behavior. apple,thermal-pressure-key now has a binding and no board fallback. These two features follow DT data without an M3-compatible gate. The existing M3 sensor-export validation and debugfs policy remain unchanged.

Migrated board	Die keys preserved, in order	Pressure key
J516s / T6030	14	mTPL
J516c / T6031	25	none
J514c / T6031	25	none

The J516s list retains its unconfirmed status; J514c retains its assumption that it matches J516c. Missing or unsupported firmware keys continue to be skipped. Install the matching DTB with the new kernel: older DTBs no longer receive the removed C fallback.

The mainline v7.3 driver and Documentation/hwmon/macsmc-hwmon.rst expose and document fan_control, but neither soc_die_keys nor board_keys. The documented fan_control override therefore stays exactly as in #639. With it unset, DT decides fan writability.

Validation completed:

• Strict checkpatch passes on each of the three new commits, with zero errors, warnings or checks. git diff --check passes.
• dt-doc-validate passes for the updated binding.
• DTValidator passes the 40 hwmon nodes reconstructed from preprocessed source, with zero schema errors.
• A source inventory comparison covers every one of the 117 Apple DTB targets in the Makefile. It resolves hwmon overrides and deletions and adds the old C fallback to the baseline. Before and after inventories are identical, including channel order, fan properties, all 64 die keys and the pressure key. Firmware-dependent discovery is recorded as a property; this does not claim runtime enumeration.

Pending validation: kernel compilation, make dt_binding_check and full dtbs_check on all Apple DTBs. The controller refused the worker's buildbox request and lease acquisition because a buildbox lease requires an operator. No buildbox SSH workaround was used. This PR remains a draft until those checks run. No target machine was accessed and no hardware test below was executed.

Owner read-only checks, with the new kernel and matching DTB installed and fan_control unset:

read_only_checks() {
    expected=$1
    tr '\0' '\n' < /proc/device-tree/compatible | grep -Fx "$expected" || return 1
    uname -r
    cat /sys/module/macsmc_hwmon/parameters/fan_control
    ls -l /sys/class/hwmon/*/fan*_target 2>/dev/null || true

    for h in /sys/class/hwmon/hwmon*; do
        [ -r "$h/name" ] || continue
        [ "$(cat "$h/name")" = macsmc_hwmon ] || continue
        for label in "$h"/temp*_label; do
            [ -r "$label" ] || continue
            printf '%s: ' "$(cat "$label")"
            cat "${label%_label}_input"
        done
        if [ -r "$h/thermal_pressure_level" ]; then
            printf 'thermal_pressure_level: '
            cat "$h/thermal_pressure_level"
        else
            printf 'thermal_pressure_level: absent\n'
        fi
    done

    aggregate=absent
    for z in /sys/class/thermal/thermal_zone*; do
        [ -r "$z/type" ] || continue
        type=$(cat "$z/type")
        printf '%s: ' "$type"
        cat "$z/temp" || printf 'temperature read failed\n'
        [ "$type" != macsmc_soc_die ] || aggregate=present
    done
    printf 'macsmc_soc_die: %s\n' "$aggregate"
}

# Run only the command matching the machine being checked:
read_only_checks apple,j616s
read_only_checks apple,j316s
read_only_checks apple,j413
read_only_checks apple,j700

# Also verify each migrated board when available:
read_only_checks apple,j516s
read_only_checks apple,j516c
read_only_checks apple,j514c

Machine	Expected fan target permissions with override unset	Die/zone check
J616s / T6040	two 0644 targets, from #639	Read cpu-die-thermal and all other existing zones above. No new macsmc_soc_die zone.
J316s / T6000	two 0444 targets	Record existing zones and temperatures; macsmc_soc_die remains absent.
J413 / T8112	no fan targets	Record existing zones and temperatures; macsmc_soc_die remains absent.
J700 / T8140	no fan targets	Read existing cpu-e0-thermal and cpu-p*-thermal temperatures above. No new macsmc_soc_die zone.

These four boards had no entries in the removed table. Their static hwmon inventory is unchanged: J616s 480 channels, J316s 13, J413 11, J700 205. On the three migrated M3 boards, check the SoC die <key> channels and macsmc_soc_die temperature; J516s should also expose thermal_pressure_level if its firmware supplies a valid mTPL key. Counts of live channels can be lower when firmware keys are missing.

J616s owner-only manual fan test, as root, after the read-only checks confirm identity, both writable targets and the default fan_control=N. Test each fan and drop each request with echo 0; the trap also drops both requests on exit or interruption:

tr '\0' '\n' < /proc/device-tree/compatible | grep -Fx apple,j616s || exit 1
h=
for candidate in /sys/class/hwmon/hwmon*; do
    [ -r "$candidate/name" ] || continue
    if [ "$(cat "$candidate/name")" = macsmc_hwmon ]; then
        h=$candidate
        break
    fi
done
test -n "$h" || exit 1
test "$(cat /sys/module/macsmc_hwmon/parameters/fan_control)" = N || exit 1
test -w "$h/fan1_target" && test -w "$h/fan2_target" || exit 1
(
    set -e
    trap 'echo 0 > "$h/fan1_target"; echo 0 > "$h/fan2_target"' EXIT
    trap 'exit 1' HUP INT TERM
    for fan in 1 2; do
        echo 3000 > "$h/fan${fan}_target"
        sleep 8
        cat "$h/fan${fan}_target" "$h/fan${fan}_input"
        echo 0 > "$h/fan${fan}_target"
        sleep 8
        cat "$h/fan${fan}_target" "$h/fan${fan}_input"
    done
)

Rollback is echo 0 to both targets. This drops the manual requests and restores the existing thermal/firmware control path; an active thermal cooling request can still keep a fan running. No reboot is required for this rollback.

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