[PATCH v1 6/7] test: dm: pmbus: add a sandbox PMBus chip emulator
Vincent Jardin
vjardin at free.fr
Thu Jul 2 19:15:50 CEST 2026
Add a UCLASS_I2C_EMUL driver that emulates a PMBus 1.x compliant chip
behind the sandbox I2C bus, plus the test.dts wiring and sandbox
defconfig that bind it to the generic PMBus regulator
(compatible = "pmbus"). This design is a stub only: it lets the
follow-up dm unit test drive lib/pmbus.c, the generic regulator and
the pmbus CLI command with no real hardware.
The emulator models a flat per-command 16-bit register file and the
three identification block strings (MFR_ID / MFR_MODEL /
MFR_REVISION). READ_IIN and READ_POUT are deliberately left
unimplemented (the chip NAKs them) so the telemetry printer's
"(not supported)" path is exercised, mirroring a real buck that only
calibrates a subset of the sensor classes.
Signed-off-by: Vincent Jardin <vjardin at free.fr>
---
MAINTAINERS | 1 +
arch/sandbox/dts/test.dts | 10 ++
configs/sandbox_defconfig | 6 +
drivers/power/regulator/Kconfig | 10 ++
drivers/power/regulator/Makefile | 1 +
drivers/power/regulator/sandbox_pmbus.c | 160 ++++++++++++++++++++++++
6 files changed, 188 insertions(+)
create mode 100644 drivers/power/regulator/sandbox_pmbus.c
diff --git a/MAINTAINERS b/MAINTAINERS
index 258c0d9bc18..bdfb660a743 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1593,6 +1593,7 @@ F: drivers/power/regulator/mpq8785.c
F: drivers/power/regulator/pmbus_generic.c
F: drivers/power/regulator/pmbus_helper.c
F: drivers/power/regulator/pmbus_helper.h
+F: drivers/power/regulator/sandbox_pmbus.c
F: drivers/thermal/pmbus_thermal.c
F: include/pmbus.h
F: lib/pmbus.c
diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index 0887de4333b..5032eecceea 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -1027,6 +1027,9 @@
emul1: emull {
compatible = "sandbox,i2c-rtc-emul";
};
+ emul_pmbus: emul-pmbus {
+ compatible = "sandbox,i2c-pmbus";
+ };
};
sandbox_pmic: sandbox_pmic at 40 {
@@ -1038,6 +1041,13 @@
reg = <0x41>;
sandbox,emul = <&emul_pmic1>;
};
+
+ pmbus at 70 {
+ reg = <0x70>;
+ compatible = "pmbus";
+ regulator-name = "sandbox-pmbus-vout";
+ sandbox,emul = <&emul_pmbus>;
+ };
};
i3c0 {
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index ba800f7d19d..de90a2b39e5 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -392,3 +392,9 @@ CONFIG_UTHREAD=y
CONFIG_UNIT_TEST=y
CONFIG_UT_TIME=y
CONFIG_UT_DM=y
+CONFIG_PMBUS=y
+CONFIG_CMD_PMBUS=y
+CONFIG_DM_REGULATOR_PMBUS_HELPER=y
+CONFIG_DM_REGULATOR_PMBUS_GENERIC=y
+CONFIG_SANDBOX_PMBUS=y
+CONFIG_PMBUS_THERMAL=y
diff --git a/drivers/power/regulator/Kconfig b/drivers/power/regulator/Kconfig
index 67c9e1fb377..143911eeb17 100644
--- a/drivers/power/regulator/Kconfig
+++ b/drivers/power/regulator/Kconfig
@@ -590,3 +590,13 @@ config DM_REGULATOR_MPQ8785
digital multiphase voltage regulators with PMBus. Supports
MPM3695, MPM3695-25, MPM82504, and MPQ8785. Adapted from the
Linux drivers/hwmon/pmbus/mpq8785.c reference.
+
+config SANDBOX_PMBUS
+ bool "Sandbox PMBus 1.x chip emulator"
+ depends on SANDBOX && PMBUS && DM_I2C
+ help
+ Emulate a PMBus 1.x compliant chip behind a sandbox I2C bus so
+ the PMBus framework (lib/pmbus.c), the generic regulator
+ (DM_REGULATOR_PMBUS_GENERIC) and the pmbus CLI command can be
+ exercised by the dm unit tests with no real hardware. Only
+ useful for testing; say N on real boards.
diff --git a/drivers/power/regulator/Makefile b/drivers/power/regulator/Makefile
index aa3faf2f34f..b8599ea7fd9 100644
--- a/drivers/power/regulator/Makefile
+++ b/drivers/power/regulator/Makefile
@@ -52,3 +52,4 @@ obj-$(CONFIG_DM_REGULATOR_MT6359) += mt6359_regulator.o
obj-$(CONFIG_DM_REGULATOR_PMBUS_HELPER) += pmbus_helper.o
obj-$(CONFIG_DM_REGULATOR_PMBUS_GENERIC) += pmbus_generic.o
obj-$(CONFIG_DM_REGULATOR_MPQ8785) += mpq8785.o
+obj-$(CONFIG_SANDBOX_PMBUS) += sandbox_pmbus.o
diff --git a/drivers/power/regulator/sandbox_pmbus.c b/drivers/power/regulator/sandbox_pmbus.c
new file mode 100644
index 00000000000..2900d0a6d83
--- /dev/null
+++ b/drivers/power/regulator/sandbox_pmbus.c
@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright 2026 Free Mobile - Vincent Jardin
+ *
+ * Sandbox PMBus 1.x chip stub (UCLASS_I2C_EMUL).
+ *
+ * Stub a DT i2c node so the PMBus framework, the generic pmbus
+ * regulator and the pmbus CLI command can be tested.
+ * The model is a flat per-command 16 bit
+ * register file combined with some fixed identification strings.
+ */
+
+#include <dm.h>
+#include <i2c.h>
+#include <pmbus.h>
+#include <linux/ctype.h>
+
+#define PMBUS_EMUL_NREG 256
+
+struct sandbox_pmbus_priv {
+ u16 reg[PMBUS_EMUL_NREG];
+ bool supported[PMBUS_EMUL_NREG];
+};
+
+/* Identification strings reported in the natural (forward) byte order. */
+static const char *pmbus_emul_string(u8 cmd)
+{
+ switch (cmd) {
+ case PMBUS_MFR_ID:
+ return "SANDBOX";
+ case PMBUS_MFR_MODEL:
+ return "PMBUS-EMUL";
+ case PMBUS_MFR_REVISION:
+ return "1.0";
+ default:
+ return NULL;
+ }
+}
+
+static int sandbox_pmbus_read(struct sandbox_pmbus_priv *priv, u8 cmd,
+ u8 *buf, int len)
+{
+ const char *str = pmbus_emul_string(cmd);
+ int i;
+
+ if (str) {
+ int slen = strlen(str);
+
+ /* Block payload: [length][bytes...]. */
+ buf[0] = (u8)slen;
+ for (i = 1; i < len; i++)
+ buf[i] = (i - 1 < slen) ? (u8)str[i - 1] : 0;
+ return 0;
+ }
+
+ if (!priv->supported[cmd])
+ return -EREMOTEIO; /* chip NAKs an unimplemented command */
+
+ for (i = 0; i < len; i++)
+ buf[i] = (u8)(priv->reg[cmd] >> (8 * i));
+ return 0;
+}
+
+static int sandbox_pmbus_write(struct sandbox_pmbus_priv *priv, u8 cmd,
+ const u8 *buf, int len)
+{
+ if (len == 0)
+ return 0; /* send-byte (eg CLEAR_FAULTS): just ACK */
+ if (!priv->supported[cmd])
+ return -EREMOTEIO;
+ if (len == 1)
+ priv->reg[cmd] = buf[0];
+ else
+ priv->reg[cmd] = (u16)buf[0] | ((u16)buf[1] << 8);
+ return 0;
+}
+
+static int sandbox_pmbus_xfer(struct udevice *emul, struct i2c_msg *msg,
+ int nmsgs)
+{
+ struct sandbox_pmbus_priv *priv = dev_get_priv(emul);
+ u8 cmd;
+
+ if (nmsgs == 0)
+ return 0;
+ /* A PMBus transaction always opens with the command-code write. */
+ if (msg[0].flags & I2C_M_RD)
+ return -EIO;
+ if (msg[0].len == 0)
+ return 0; /* address-only probe */
+ cmd = msg[0].buf[0];
+
+ if (nmsgs >= 2 && (msg[1].flags & I2C_M_RD))
+ return sandbox_pmbus_read(priv, cmd, msg[1].buf, msg[1].len);
+
+ return sandbox_pmbus_write(priv, cmd, msg[0].buf + 1, msg[0].len - 1);
+}
+
+static void sandbox_pmbus_support(struct sandbox_pmbus_priv *priv, u8 cmd,
+ u16 val)
+{
+ priv->supported[cmd] = true;
+ priv->reg[cmd] = val;
+}
+
+static int sandbox_pmbus_probe(struct udevice *emul)
+{
+ struct sandbox_pmbus_priv *priv = dev_get_priv(emul);
+
+ /* Configuration / identification. */
+ sandbox_pmbus_support(priv, PMBUS_PAGE, 0);
+ sandbox_pmbus_support(priv, PMBUS_OPERATION, PB_OPERATION_ON);
+ sandbox_pmbus_support(priv, PMBUS_ON_OFF_CONFIG, 0);
+ sandbox_pmbus_support(priv, PMBUS_WRITE_PROTECT, 0);
+ sandbox_pmbus_support(priv, PMBUS_CAPABILITY, 0xb0);
+ sandbox_pmbus_support(priv, PMBUS_VOUT_MODE, 0x18); /* LINEAR 2^-8 */
+ sandbox_pmbus_support(priv, PMBUS_VOUT_COMMAND, 0x0200);
+ sandbox_pmbus_support(priv, PMBUS_VOUT_TRIM, 0);
+ sandbox_pmbus_support(priv, PMBUS_VOUT_MAX, 0x0400);
+ sandbox_pmbus_support(priv, PMBUS_VOUT_SCALE_LOOP, 0);
+ sandbox_pmbus_support(priv, PMBUS_REVISION, PMBUS_REV_13);
+
+ /* Status registers, all clean. */
+ sandbox_pmbus_support(priv, PMBUS_STATUS_BYTE, 0);
+ sandbox_pmbus_support(priv, PMBUS_STATUS_WORD, 0);
+ sandbox_pmbus_support(priv, PMBUS_STATUS_VOUT, 0);
+ sandbox_pmbus_support(priv, PMBUS_STATUS_IOUT, 0);
+ sandbox_pmbus_support(priv, PMBUS_STATUS_INPUT, 0);
+ sandbox_pmbus_support(priv, PMBUS_STATUS_TEMPERATURE, 0);
+ sandbox_pmbus_support(priv, PMBUS_STATUS_CML, 0);
+
+ /*
+ * Telemetry the emulated chip implements. READ_IIN and READ_POUT
+ * are intentionally absent so callers see the unsupported path.
+ */
+ sandbox_pmbus_support(priv, PMBUS_READ_VIN, 0x0abc);
+ sandbox_pmbus_support(priv, PMBUS_READ_VOUT, 0x0200);
+ sandbox_pmbus_support(priv, PMBUS_READ_IOUT, 0x0123);
+ sandbox_pmbus_support(priv, PMBUS_READ_TEMPERATURE_1, 0x0019);
+
+ return 0;
+}
+
+static struct dm_i2c_ops sandbox_pmbus_emul_ops = {
+ .xfer = sandbox_pmbus_xfer,
+};
+
+static const struct udevice_id sandbox_pmbus_ids[] = {
+ { .compatible = "sandbox,i2c-pmbus" },
+ { }
+};
+
+U_BOOT_DRIVER(sandbox_pmbus_emul) = {
+ .name = "sandbox_pmbus_emul",
+ .id = UCLASS_I2C_EMUL,
+ .of_match = sandbox_pmbus_ids,
+ .probe = sandbox_pmbus_probe,
+ .priv_auto = sizeof(struct sandbox_pmbus_priv),
+ .ops = &sandbox_pmbus_emul_ops,
+};
--
2.43.0
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