Re: [PATCH v2 1/1] tty: i3c: add TTY over I3C master support

[Greg KH <gregkh@linuxfoundation.org>]

Note, your subject line needs to change.

On Fri, Oct 20, 2023 at 12:00:27PM -0400, Frank Li wrote:
> In typical embedded Linux systems, UART consoles require at least two pins,
> TX and RX. In scenarios where I2C/I3C devices like sensors or PMICs are
> present, we can save these two pins by using this driver. Pins is crucial

"Pins are crucial"

> resources, especially in small chip packages.
> 
> This introduces support for using the I3C bus to transfer console tty data,
> effectively replacing the need for dedicated UART pins. This not only
> conserves valuable pin resources but also facilitates testing of I3C's
> advanced features, including early termination, in-band interrupt (IBI)
> support, and the creation of more complex data patterns. Additionally,
> it aids in identifying and addressing issues within the I3C controller
> driver.

But where is the serial data ending up at?  Not a normal uart, what is
on the other end?  And do line settings mean anything here?

> 
> Signed-off-by: Frank Li <Frank.Li@nxp.com>
> ---
> 
> Notes:
>     This patch depend on
>     https://lore.kernel.org/imx/20231018205929.3435110-1-Frank.Li@nxp.com/T/#t

Let's wait for those to be accepted first, right?

> +static DEFINE_IDR(i3c_tty_minors);
> +static DEFINE_MUTEX(i3c_tty_minors_lock);

I thought idr didn't need a mutex anymore, are you sure this is still
needed?

> +static struct tty_driver *i3c_tty_driver;
> +
> +#define I3C_TTY_MINORS		256

Do you really need 256 minors?

> +#define I3C_TTY_TRANS_SIZE	16
> +#define I3C_TTY_RX_STOP		0
> +#define I3C_TTY_RETRY		20
> +#define I3C_TTY_YIELD_US	100
> +
> +struct ttyi3c_port {
> +	struct tty_port port;
> +	int minor;
> +	spinlock_t xlock; /* protect xmit */
> +	char tx_buff[I3C_TTY_TRANS_SIZE];
> +	char rx_buff[I3C_TTY_TRANS_SIZE];
> +	struct i3c_device *i3cdev;
> +	struct work_struct txwork;
> +	struct work_struct rxwork;
> +	struct completion txcomplete;
> +	unsigned long status;
> +	int buf_overrun;

You set buf_overrun but never do anything with it.  Why care about it?

Other than these minor things, looks sane, nice work.

thanks,

greg k-h