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.ander...@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
> *
>
