[PATCH] i2c: muxes: Add PCA9541 i2c arbitrator driver
Padmarao Begari
padmarao.begari at amd.com
Mon Jun 23 10:24:39 CEST 2025
Add a driver for the PCA9541 i2c bus arbitrator based
on the Linux driver for the same device.
Co-developed-by: Jonathan Stroud <jonathan.stroud at amd.com>
Signed-off-by: Jonathan Stroud <jonathan.stroud at amd.com>
Signed-off-by: Padmarao Begari <padmarao.begari at amd.com>
---
drivers/i2c/muxes/Kconfig | 7 +
drivers/i2c/muxes/Makefile | 1 +
drivers/i2c/muxes/pca9541.c | 297 ++++++++++++++++++++++++++++++++++++
3 files changed, 305 insertions(+)
create mode 100644 drivers/i2c/muxes/pca9541.c
diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
index cd5579aa55a..65319bb6fd8 100644
--- a/drivers/i2c/muxes/Kconfig
+++ b/drivers/i2c/muxes/Kconfig
@@ -25,6 +25,13 @@ config I2C_ARB_GPIO_CHALLENGE
response mechanism where masters have to claim the bus by asserting
a GPIO.
+config I2C_MUX_PCA9541
+ tristate "NXP PCA9541 I2C Master Selector"
+ depends on I2C_MUX
+ help
+ If you say yes here you get support for the NXP PCA9541
+ I2C Master Selector.
+
config I2C_MUX_PCA954x
tristate "TI PCA954x I2C Mux/switches"
depends on I2C_MUX
diff --git a/drivers/i2c/muxes/Makefile b/drivers/i2c/muxes/Makefile
index b690821199f..844d4520e43 100644
--- a/drivers/i2c/muxes/Makefile
+++ b/drivers/i2c/muxes/Makefile
@@ -3,5 +3,6 @@
# Copyright (c) 2015 Google, Inc
obj-$(CONFIG_I2C_ARB_GPIO_CHALLENGE) += i2c-arb-gpio-challenge.o
obj-$(CONFIG_I2C_MUX) += i2c-mux-uclass.o
+obj-$(CONFIG_I2C_MUX_PCA9541) += pca9541.o
obj-$(CONFIG_I2C_MUX_PCA954x) += pca954x.o
obj-$(CONFIG_I2C_MUX_GPIO) += i2c-mux-gpio.o
diff --git a/drivers/i2c/muxes/pca9541.c b/drivers/i2c/muxes/pca9541.c
new file mode 100644
index 00000000000..021088acaee
--- /dev/null
+++ b/drivers/i2c/muxes/pca9541.c
@@ -0,0 +1,297 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2008-2009 Rodolfo Giometti <giometti at linux.it>
+ * Copyright (c) 2008-2009 Eurotech S.p.A. <info at eurotech.it>
+ * Copyright (c) 2010 Ericsson AB.
+ * Copyright (c) 2025 Advanced Micro Devices, Inc.
+ */
+
+#include <dm.h>
+#include <errno.h>
+#include <i2c.h>
+#include <log.h>
+#include <malloc.h>
+#include <linux/delay.h>
+
+/*
+ * The PCA9541 is a bus master selector. It supports two I2C masters connected
+ * to a single slave bus.
+ *
+ * Before each bus transaction, a master has to acquire bus ownership. After the
+ * transaction is complete, bus ownership has to be released. This fits well
+ * into the I2C multiplexer framework, which provides select and release
+ * functions for this purpose. For this reason, this driver is modeled as
+ * single-channel I2C bus multiplexer.
+ *
+ * This driver assumes that the two bus masters are controlled by two different
+ * hosts. If a single host controls both masters, platform code has to ensure
+ * that only one of the masters is instantiated at any given time.
+ */
+
+#define PCA9541_CONTROL 0x01
+#define PCA9541_ISTAT 0x02
+
+#define PCA9541_CTL_MYBUS BIT(0)
+#define PCA9541_CTL_NMYBUS BIT(1)
+#define PCA9541_CTL_BUSON BIT(2)
+#define PCA9541_CTL_NBUSON BIT(3)
+#define PCA9541_CTL_BUSINIT BIT(4)
+#define PCA9541_CTL_TESTON BIT(6)
+#define PCA9541_CTL_NTESTON BIT(7)
+
+#define PCA9541_ISTAT_INTIN BIT(0)
+#define PCA9541_ISTAT_BUSINIT BIT(1)
+#define PCA9541_ISTAT_BUSOK BIT(2)
+#define PCA9541_ISTAT_BUSLOST BIT(3)
+#define PCA9541_ISTAT_MYTEST BIT(6)
+#define PCA9541_ISTAT_NMYTEST BIT(7)
+
+#define BUSON (PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON)
+#define MYBUS (PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS)
+
+/* arbitration timeouts, in jiffies */
+#define ARB_TIMEOUT_US 125000 /* 125 ms until forcing bus ownership */
+#define ARB2_TIMEOUT_US 250000 /* 250 ms until acquisition failure */
+
+/* arbitration retry delays, in us */
+#define SELECT_DELAY_SHORT 50
+#define SELECT_DELAY_LONG 1000
+
+struct pca9541_plat {
+ u32 addr;
+};
+
+struct pca9541_priv {
+ u32 addr;
+ unsigned long select_timeout;
+ long arb_timeout;
+};
+
+static inline int mybus(int x)
+{
+ return !(x & MYBUS) || ((x & MYBUS) == MYBUS);
+}
+
+static inline int busoff(int x)
+{
+ return !(x & BUSON) || ((x & BUSON) == BUSON);
+}
+
+static int pca9541_reg_write(struct udevice *mux, struct pca9541_priv *client,
+ u8 command, u8 val)
+{
+ return dm_i2c_write(mux, command, &val, 1);
+}
+
+static int pca9541_reg_read(struct udevice *mux, struct pca9541_priv *client,
+ u8 command)
+{
+ int ret;
+ uchar byte;
+
+ ret = dm_i2c_read(mux, command, &byte, 1);
+
+ return ret ?: byte;
+}
+
+/*
+ * Arbitration management functions
+ */
+
+/* Release bus. Also reset NTESTON and BUSINIT if it was set. */
+static void pca9541_release_bus(struct udevice *mux, struct pca9541_priv *client)
+{
+ int reg;
+
+ reg = pca9541_reg_read(mux, client, PCA9541_CONTROL);
+ if (reg >= 0 && !busoff(reg) && mybus(reg))
+ pca9541_reg_write(mux, client, PCA9541_CONTROL,
+ (reg & PCA9541_CTL_NBUSON) >> 1);
+}
+
+/*
+ * Arbitration is defined as a two-step process. A bus master can only activate
+ * the slave bus if it owns it; otherwise it has to request ownership first.
+ * This multi-step process ensures that access contention is resolved
+ * gracefully.
+ *
+ * Bus Ownership Other master Action
+ * state requested access
+ * ----------------------------------------------------
+ * off - yes wait for arbitration timeout or
+ * for other master to drop request
+ * off no no take ownership
+ * off yes no turn on bus
+ * on yes - done
+ * on no - wait for arbitration timeout or
+ * for other master to release bus
+ *
+ * The main contention point occurs if the slave bus is off and both masters
+ * request ownership at the same time. In this case, one master will turn on
+ * the slave bus, believing that it owns it. The other master will request
+ * bus ownership. Result is that the bus is turned on, and master which did
+ * _not_ own the slave bus before ends up owning it.
+ */
+
+/* Control commands per PCA9541 datasheet */
+static const u8 pca9541_control[16] = {
+ 4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
+};
+
+/*
+ * Channel arbitration
+ *
+ * Return values:
+ * <0: error
+ * 0 : bus not acquired
+ * 1 : bus acquired
+ */
+static int pca9541_arbitrate(struct udevice *mux, struct pca9541_priv *client)
+{
+ int reg, ret = 0;
+
+ reg = pca9541_reg_read(mux, client, PCA9541_CONTROL);
+ if (reg < 0)
+ return reg;
+
+ if (busoff(reg)) {
+ int istat;
+
+ /*
+ * Bus is off. Request ownership or turn it on unless
+ * other master requested ownership.
+ */
+ istat = pca9541_reg_read(mux, client, PCA9541_ISTAT);
+ if (!(istat & PCA9541_ISTAT_NMYTEST) ||
+ client->arb_timeout <= 0) {
+ /*
+ * Other master did not request ownership,
+ * or arbitration timeout expired. Take the bus.
+ */
+ pca9541_reg_write(mux, client, PCA9541_CONTROL,
+ pca9541_control[reg & 0x0f]
+ | PCA9541_CTL_NTESTON);
+ client->select_timeout = SELECT_DELAY_SHORT;
+ } else {
+ /*
+ * Other master requested ownership.
+ * Set extra long timeout to give it time to acquire it.
+ */
+ client->select_timeout = SELECT_DELAY_LONG * 2;
+ }
+ } else if (mybus(reg)) {
+ /*
+ * Bus is on, and we own it. We are done with acquisition.
+ * Reset NTESTON and BUSINIT, then return success.
+ */
+ if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT))
+ pca9541_reg_write(mux, client, PCA9541_CONTROL,
+ reg & ~(PCA9541_CTL_NTESTON
+ | PCA9541_CTL_BUSINIT));
+ ret = 1;
+ } else {
+ /*
+ * Other master owns the bus.
+ * If arbitration timeout has expired, force ownership.
+ * Otherwise request it.
+ */
+ client->select_timeout = SELECT_DELAY_LONG;
+ if (client->arb_timeout <= 0) {
+ /* Time is up, take the bus and reset it. */
+ pca9541_reg_write(mux, client, PCA9541_CONTROL,
+ pca9541_control[reg & 0x0f]
+ | PCA9541_CTL_BUSINIT
+ | PCA9541_CTL_NTESTON);
+ } else {
+ /* Request bus ownership if needed */
+ if (!(reg & PCA9541_CTL_NTESTON))
+ pca9541_reg_write(mux, client, PCA9541_CONTROL,
+ reg | PCA9541_CTL_NTESTON);
+ }
+ }
+
+ return ret;
+}
+
+static int pca9541_select_chan(struct udevice *mux, struct udevice *bus,
+ uint channel)
+{
+ struct pca9541_priv *priv = dev_get_priv(mux);
+ int ret;
+ long timeout = ARB2_TIMEOUT_US; /* Give up after this time */
+
+ /* Force bus ownership after this time */
+ priv->arb_timeout = ARB_TIMEOUT_US;
+ do {
+ ret = pca9541_arbitrate(mux, priv);
+ if (ret)
+ return ret < 0 ? ret : 0;
+
+ udelay(priv->select_timeout);
+ timeout -= priv->select_timeout;
+ priv->arb_timeout -= priv->select_timeout;
+ } while (timeout > 0);
+
+ debug("I2C Arbitration select timeout\n");
+
+ return -ETIMEDOUT;
+}
+
+static int pca9541_release_chan(struct udevice *mux, struct udevice *bus,
+ uint channel)
+{
+ struct pca9541_priv *priv = dev_get_priv(mux);
+
+ pca9541_release_bus(mux, priv);
+
+ return 0;
+}
+
+/*
+ * I2C init/probing/exit functions
+ */
+static int pca9541_of_to_plat(struct udevice *dev)
+{
+ struct pca9541_plat *plat = dev_get_plat(dev);
+
+ plat->addr = dev_read_u32_default(dev, "reg", 0);
+ if (!plat->addr) {
+ debug("Reg property is not found\n");
+ return -ENODEV;
+ }
+
+ debug("Device %s at 0x%x\n", dev->name, plat->addr);
+
+ return 0;
+}
+
+static int pca9541_probe(struct udevice *dev)
+{
+ struct pca9541_plat *plat = dev_get_plat(dev);
+ struct pca9541_priv *priv = dev_get_priv(dev);
+
+ priv->addr = plat->addr;
+
+ return 0;
+}
+
+static const struct i2c_mux_ops pca9541_ops = {
+ .select = pca9541_select_chan,
+ .deselect = pca9541_release_chan,
+};
+
+static const struct udevice_id pca9541_ids[] = {
+ { .compatible = "nxp,pca9541", },
+ { }
+};
+
+U_BOOT_DRIVER(pca9541) = {
+ .name = "pca9541",
+ .id = UCLASS_I2C_MUX,
+ .of_match = pca9541_ids,
+ .probe = pca9541_probe,
+ .ops = &pca9541_ops,
+ .of_to_plat = pca9541_of_to_plat,
+ .plat_auto = sizeof(struct pca9541_plat),
+ .priv_auto = sizeof(struct pca9541_priv),
+};
--
2.25.1
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