Re: [PATCH] USB: serial: ftdi_sio: add support for FT232H CBUS gpios

[Johan Hovold <johan@kernel.org>]

On Thu, Aug 08, 2019 at 10:23:48PM +0000, Matthew Michilot wrote:
> Enable support for cbus gpios on FT232H. The cbus configuration is
> stored in one word in the EEPROM at byte-offset 0x1a with the mux

It seems to be stored in two words.

> config for ACBUS5, ACBUS6, ACBUS8 and ACBUS9 (only pins that can be
> configured as I/O mode).
> 
> Tested using FT232H by configuring one ACBUS pin at a time.
> 
> Review-by: Tim Harvey <tharvey@gateworks.com>

typo: Reviewed-by

> Signed-off-by: Matthew Michilot <matthew.michilot@gmail.com>
> ---
>  drivers/usb/serial/ftdi_sio.c | 43 +++++++++++++++++++++++++++++++++++
>  1 file changed, 43 insertions(+)
> 
> diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
> index 4b3a049561f3..c8d35faa8f61 100644
> --- a/drivers/usb/serial/ftdi_sio.c
> +++ b/drivers/usb/serial/ftdi_sio.c
> @@ -2023,6 +2023,46 @@ static int ftdi_read_eeprom(struct usb_serial *serial, void *dst, u16 addr,
>  	return 0;
>  }
>  
> +static int ftdi_gpio_init_ft232h(struct usb_serial_port *port)
> +{
> +	struct ftdi_private *priv = usb_get_serial_port_data(port);
> +	u8 *buf;
> +	u16 cbus_config;
> +	int ret;
> +	int i;
> +
> +	buf = kmalloc(2, GFP_KERNEL);
> +	if (!buf)
> +		return -ENOMEM;
> +
> +	ret = ftdi_read_eeprom(port->serial, buf, 0x1A, 4);

You allocate 2 byte above, but write 4 bytes into buf here.

Please also use lower-case hex notation consistently throughout.

> +	if (ret < 0)
> +		goto out_free;
> +
> +	/*
> +	 * FT232H CBUS Memory Map
> +	 *
> +	 * 0x1A: 8X (upper nibble -> AC5)
> +	 * 0x1B: X8 (lower nibble -> AC6)
> +	 * 0x1C: 88 (upper nibble -> AC8 | lower nibble -> AC9)
> +	 */
> +	cbus_config = (((buf[0] & 0xf0) | (buf[1] & 0xf)) << 8 | buf[2]);

Have you verified the order you use here by enabling one gpio at a time
and toggling it? The reason I ask is that the above would give a
mapping of

	gpio0 -> AC9
	gpio1 -> AC8
	gpio2 -> AC6
	gpio4 -> AC5

which looks backwards but may be correct.

Also please drop the outer parentheses in the above expression.

> +
> +	priv->gc.ngpio = 4;
> +	priv->gpio_altfunc = 0xff;
> +
> +	for (i = 0; i < priv->gc.ngpio; ++i) {
> +		if ((cbus_config & 0xf) == FTDI_FTX_CBUS_MUX_GPIO)
> +			priv->gpio_altfunc &= ~BIT(i);
> +		cbus_config >>= 4;
> +	}
> +
> +out_free:
> +	kfree(buf);
> +
> +	return ret;
> +}
> +
>  static int ftdi_gpio_init_ft232r(struct usb_serial_port *port)
>  {
>  	struct ftdi_private *priv = usb_get_serial_port_data(port);
> @@ -2104,6 +2144,9 @@ static int ftdi_gpio_init(struct usb_serial_port *port)
>  	case FTX:
>  		result = ftdi_gpio_init_ftx(port);
>  		break;
> +	case FT232H:
> +		result = ftdi_gpio_init_ft232h(port);
> +		break;

Please keep the case labels sorted alphabetically.

>  	default:
>  		return 0;
>  	}

Johan