Re: [PATCH v2 2/3] can: mcp251xfd: add support for XSTBYEN transceiver standby control

[Marc Kleine-Budde]

On 16.03.2026 18:49:49, Viken Dadhaniya wrote:
> The MCP251xFD has a dedicated transceiver standby control function on
> the INT0/GPIO0/XSTBY pin, controlled by the XSTBYEN bit in IOCON.

Please add a check to mcp251xfd_gpio_request() that GPIO0 cannot be used
with xstbyen.

> 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@xxxxxxxxxxxxxxxx>
> ---
>  .../net/can/spi/mcp251xfd/mcp251xfd-core.c    | 30 +++++++++++++++++++
>  drivers/net/can/spi/mcp251xfd/mcp251xfd.h     |  1 +
>  2 files changed, 31 insertions(+)
>
> diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
> index 9c86df08c2c5..7a152acf4931 100644
> --- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
> +++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
> @@ -764,6 +764,29 @@ 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.
> +	 *
> +	 * Once configured, the hardware automatically drives the pin HIGH
> +	 * on Sleep mode entry and LOW on Sleep mode exit.
> +	 */

What does the pin do in Config mode?

> +	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;
> @@ -800,6 +823,12 @@ static int mcp251xfd_chip_start(struct mcp251xfd_priv *priv)
>  	if (err)
>  		goto out_chip_stop;
>
> +	if (priv->xstbyen) {
> +		err = mcp251xfd_chip_xstbyen_enable(priv);
> +		if (err)
> +			goto out_chip_stop;
> +	}
> +

You should configure the pin before bringing the controller into normale mode.

regards,
Marc

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