[PATCH net-next 4/6] can: mcp251xfd: add support for XSTBYEN transceiver standby control

Marc Kleine-Budde
2026-04-01T07:33:55Z

From: Viken Dadhaniya <viken.dadhaniya@oss.qualcomm.com>

The MCP251xFD has a dedicated transceiver standby control function on
the INT0/GPIO0/XSTBY pin, controlled by the XSTBYEN bit in IOCON.
When enabled, the hardware automatically manages the transceiver
standby state: the pin is driven low when the controller is active
and high when it enters Sleep mode.

Enable this feature when the 'microchip,xstbyen' device tree property
is present.

Signed-off-by: Viken Dadhaniya <viken.dadhaniya@oss.qualcomm.com>
Link: https://patch.msgid.link/20260321135031.3107408-3-viken.dadhaniya@oss.qualcomm.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
.../net/can/spi/mcp251xfd/mcp251xfd-core.c | 37 +++++++++++++++++++
drivers/net/can/spi/mcp251xfd/mcp251xfd.h | 1 +
2 files changed, 38 insertions(+)

diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
index 9c86df08c2c5..92a86083c896 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
@@ -764,6 +764,31 @@ static void mcp251xfd_chip_stop(struct mcp251xfd_priv *priv,
mcp251xfd_chip_set_mode(priv, MCP251XFD_REG_CON_MODE_CONFIG);
}

+static int mcp251xfd_chip_xstbyen_enable(const struct mcp251xfd_priv *priv)
+{
+ /* Configure the INT0/GPIO0/XSTBY pin as transceiver standby control:
+ *
+ * - XSTBYEN=1: route the pin to the transceiver standby function
+ * - TRIS0=0: set output direction; the reset default is 1 (input),
+ * which leaves the pin floating HIGH and keeps the
+ * transceiver in standby regardless of XSTBYEN
+ * - LAT0=0: drive pin LOW => transceiver active (not in standby)
+ *
+ * All three bits are included in the mask; only XSTBYEN is set in
+ * val, so TRIS0 and LAT0 are cleared to 0 atomically.
+ *
+ * Pin behaviour by mode:
+ * - Config mode: controlled by LAT0 (LAT0=0 => LOW => active)
+ * - Normal mode: hardware drives pin LOW (active)
+ * - Sleep mode: hardware drives pin HIGH (standby)
+ */
+ return regmap_update_bits(priv->map_reg, MCP251XFD_REG_IOCON,
+ MCP251XFD_REG_IOCON_XSTBYEN |
+ MCP251XFD_REG_IOCON_TRIS0 |
+ MCP251XFD_REG_IOCON_LAT0,
+ MCP251XFD_REG_IOCON_XSTBYEN);
+}
+
static int mcp251xfd_chip_start(struct mcp251xfd_priv *priv)
{
int err;
@@ -796,6 +821,12 @@ static int mcp251xfd_chip_start(struct mcp251xfd_priv *priv)

priv->can.state = CAN_STATE_ERROR_ACTIVE;

+ if (priv->xstbyen) {
+ err = mcp251xfd_chip_xstbyen_enable(priv);
+ if (err)
+ goto out_chip_stop;
+ }
+
err = mcp251xfd_chip_set_normal_mode(priv);
if (err)
goto out_chip_stop;
@@ -1805,6 +1836,11 @@ static int mcp251xfd_gpio_request(struct gpio_chip *chip, unsigned int offset)
u32 pin_mask = MCP251XFD_REG_IOCON_PM(offset);
int ret;

+ if (priv->xstbyen && offset == 0) {
+ netdev_err(priv->ndev, "Can't use GPIO 0 with XSTBYEN!\n");
+ return -EINVAL;
+ }
+
if (priv->rx_int && offset == 1) {
netdev_err(priv->ndev, "Can't use GPIO 1 with RX-INT!\n");
return -EINVAL;
@@ -2271,6 +2307,7 @@ static int mcp251xfd_probe(struct spi_device *spi)
priv->pll_enable = pll_enable;
priv->reg_vdd = reg_vdd;
priv->reg_xceiver = reg_xceiver;
+ priv->xstbyen = device_property_present(&spi->dev, "microchip,xstbyen");
priv->devtype_data = *(struct mcp251xfd_devtype_data *)spi_get_device_match_data(spi);

/* Errata Reference:
diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
index 085d7101e595..d3f4704e2678 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
@@ -672,6 +672,7 @@ struct mcp251xfd_priv {
struct gpio_desc *rx_int;
struct clk *clk;
bool pll_enable;
+ bool xstbyen;
struct regulator *reg_vdd;
struct regulator *reg_xceiver;

--
2.53.0