[PATCH 2/5] fsi: aspeed: Support cabled FSI

[Andrew Jeffery]

On Tue, 28 Jul 2020, at 12:25, Joel Stanley wrote:
> Some FSI capable systems have internal FSI signals, and some have
> external cabled FSI. Software can detect which machine this is by
> reading a jumper GPIO, and also control which pins the signals are
> routed to through a mux GPIO.
> 
> This attempts to find the GPIOs at probe time. If they are not present
> in the device tree the driver will not error and continue as before.
> 
> The mux GPIO is owned by the FSI driver to ensure it is not modified at
> runtime. The routing jumper obtained as non-exclusive to allow other
> software to inspect it's state.
> 
> Signed-off-by: Joel Stanley <joel at jms.id.au>
> ---
>  drivers/fsi/fsi-master-aspeed.c | 46 +++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/drivers/fsi/fsi-master-aspeed.c b/drivers/fsi/fsi-master-aspeed.c
> index 2b8ca72baeb5..c282de76e6e7 100644
> --- a/drivers/fsi/fsi-master-aspeed.c
> +++ b/drivers/fsi/fsi-master-aspeed.c
> @@ -13,6 +13,7 @@
>  #include <linux/regmap.h>
>  #include <linux/slab.h>
>  #include <linux/iopoll.h>
> +#include <linux/gpio/consumer.h>
>  
>  #include "fsi-master.h"
>  
> @@ -417,6 +418,45 @@ static int aspeed_master_init(struct 
> fsi_master_aspeed *aspeed)
>  	return 0;
>  }
>  
> +static int tacoma_cabled_fsi_fixup(struct device *dev)
> +{
> +	struct gpio_desc *routing_gpio, *mux_gpio;
> +	int gpio;
> +
> +	/*
> +	 * The routing GPIO is a jumper indicating we should mux for the
> +	 * externally connected FSI cable.
> +	 */
> +	routing_gpio = devm_gpiod_get_optional(dev, "fsi-routing",
> +			GPIOD_IN | GPIOD_FLAGS_BIT_NONEXCLUSIVE);
> +	if (IS_ERR(routing_gpio))
> +		return PTR_ERR(routing_gpio);
> +	if (!routing_gpio)
> +		return 0;
> +
> +	mux_gpio = devm_gpiod_get_optional(dev, "fsi-mux", GPIOD_ASIS);
> +	if (IS_ERR(mux_gpio))
> +		return PTR_ERR(mux_gpio);
> +	if (!mux_gpio)
> +		return 0;
> +
> +	gpio = gpiod_get_value(routing_gpio);
> +	if (gpio < 0)
> +		return gpio;
> +
> +	/* If the routing GPIO is high we should set the mux to low. */
> +	if (gpio) {
> +		gpiod_direction_output(mux_gpio, 0);
> +		dev_info(dev, "FSI configured for external cable\n");
> +	} else {
> +		gpiod_direction_output(mux_gpio, 1);
> +	}

I haven't checked this logic against the hardware but the rest of the patch 
looks okay.

Reviewed-by: Andrew Jeffery <andrew at aj.id.au>