[PATCH v2 26/28] serial: dm: Add support for puts

[Sean Anderson]

On 3/10/22 3:50 PM, Sean Anderson wrote:
> Some serial drivers can be vastly more efficient when printing multiple
> characters at once. Non-DM serial has had a puts option for these sorts
> of drivers; implement it for DM serial as well.
> 
> Because we have to add carriage returns, we can't just pass the whole
> string directly to the serial driver. Instead, we print up to the
> newline, then print a carriage return, and then continue on. This is
> less efficient, but it is better than printing each character
> individually. It also avoids having to allocate memory just to add a few
> characters.
> 
> Drivers may perform short writes (such as filling a FIFO) and return the
> number of characters written in len. We loop over them in the same way
> that _serial_putc loops over putc.
> 
> This results in around 148 bytes of bloat for all boards with DM_SERIAL
> enabled:
> 
> vexpress_aemv8a_juno: all +148 rodata +8 text +140
>    u-boot: add: 2/0, grow: 0/-2 bytes: 232/-92 (140)
> 	 function                                   old     new   delta
> 	 _serial_puts                                 -     200    +200
> 	 strchrnul                                    -      32     +32
> 	 serial_puts                                 68      24     -44
> 	 serial_stub_puts                            56       8     -48
> 
> Signed-off-by: Sean Anderson <sean.anderson at seco.com>
> ---
> 
> Changes in v2:
> - New
> 
>  drivers/serial/serial-uclass.c | 27 +++++++++++++++++++++++++--
>  include/serial.h               | 18 ++++++++++++++++++
>  2 files changed, 43 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/serial/serial-uclass.c b/drivers/serial/serial-uclass.c
> index 362cedd955..352ad986f7 100644
> --- a/drivers/serial/serial-uclass.c
> +++ b/drivers/serial/serial-uclass.c
> @@ -199,8 +199,31 @@ static void _serial_putc(struct udevice *dev, char ch)
>  
>  static void _serial_puts(struct udevice *dev, const char *str)
>  {
> -	while (*str)
> -		_serial_putc(dev, *str++);
> +	struct dm_serial_ops *ops = serial_get_ops(dev);
> +
> +	if (!ops->puts) {
> +		while (*str)
> +			_serial_putc(dev, *str++);

This is missing an early return. Will be fixed in v3.

--Sean

> +	}
> +
> +	do {
> +		const char *newline = strchrnul(str, '\n');
> +		size_t len = newline - str + !!*newline;
> +
> +		do {
> +			int err;
> +			size_t written = len;
> +
> +			err = ops->puts(dev, str, &written);
> +			if (err && err != -EAGAIN)
> +				return;
> +			str += written;
> +			len -= written;
> +		} while (len);
> +
> +		if (*newline)
> +			_serial_putc(dev, '\r');
> +	} while (*str);
>  }
>  
>  static int __serial_getc(struct udevice *dev)
> diff --git a/include/serial.h b/include/serial.h
> index 2681d26c82..ea96d904d8 100644
> --- a/include/serial.h
> +++ b/include/serial.h
> @@ -195,6 +195,24 @@ struct dm_serial_ops {
>  	 * @return 0 if OK, -ve on error
>  	 */
>  	int (*putc)(struct udevice *dev, const char ch);
> +	/**
> +	 * puts() - Write a string
> +	 *
> +	 * This writes a string. This function should be implemented only if
> +	 * writing multiple characters at once is more performant than just
> +	 * calling putc() in a loop.
> +	 *
> +	 * If the whole string cannot be written at once, then @len should be
> +	 * set to the number of characters written, and this function should
> +	 * return -EAGAIN.
> +	 *
> +	 * @dev: Device pointer
> +	 * @s: The string to write
> +	 * @len: The length of the string to write. This should be set to the
> +	 *       number of characters actually written on return.
> +	 * @return 0 if OK, -ve on error
> +	 */
> +	int (*puts)(struct udevice *dev, const char *s, size_t *len);
>  	/**
>  	 * pending() - Check if input/output characters are waiting
>  	 *
>