[PATCH 4/4] lib: utils/serial: Ensure baudrate is non-zero before using

[Anup Patel]

On Mon, Jul 18, 2022 at 10:50 PM Andrew Jones <ajones at ventanamicro.com> wrote:
>
> RISC-V doesn't generate exceptions on divide-by-zero, but the result,
> all bits set, is not likely what people expect either. In all cases
> where we divide by baudrate there's a chance it's zero (when the DT
> it came from is "bad"). To avoid difficult to debug situations, leave
> baudrate dependent registers alone when baudrate is zero, as, also in
> all cases, it appears we can skip initialization of those registers
> and still [hopefully] have a functioning UART.
>
> Signed-off-by: Andrew Jones <ajones at ventanamicro.com>

Looks good to me.

Reviewed-by: Anup Patel <anup at brainfault.org>

Regards,
Anup

> ---
>  lib/utils/serial/gaisler-uart.c | 2 +-
>  lib/utils/serial/shakti-uart.c  | 8 ++++++--
>  lib/utils/serial/sifive-uart.c  | 2 +-
>  lib/utils/serial/uart8250.c     | 7 +++++--
>  4 files changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/lib/utils/serial/gaisler-uart.c b/lib/utils/serial/gaisler-uart.c
> index 5f30ee43b719..eec75cca0c98 100644
> --- a/lib/utils/serial/gaisler-uart.c
> +++ b/lib/utils/serial/gaisler-uart.c
> @@ -70,7 +70,7 @@ int gaisler_uart_init(unsigned long base, u32 in_freq, u32 baudrate)
>         uart_base = (volatile char *)base;
>
>         /* Configure baudrate */
> -       if (in_freq)
> +       if (in_freq && baudrate)
>                 set_reg(UART_REG_SCALER, in_freq / (baudrate * 8 + 7));
>
>         ctrl = get_reg(UART_REG_CTRL);
> diff --git a/lib/utils/serial/shakti-uart.c b/lib/utils/serial/shakti-uart.c
> index 5f2fe75c9f33..2f09f141b9cf 100644
> --- a/lib/utils/serial/shakti-uart.c
> +++ b/lib/utils/serial/shakti-uart.c
> @@ -47,8 +47,12 @@ static struct sbi_console_device shakti_console = {
>  int shakti_uart_init(unsigned long base, u32 in_freq, u32 baudrate)
>  {
>         uart_base = (volatile char *)base;
> -       u16 baud = (u16)(in_freq/(16 * baudrate));
> -       writew(baud, uart_base + REG_BAUD);
> +       u16 baud;
> +
> +       if (baudrate) {
> +               baud = (u16)(in_freq / (16 * baudrate));
> +               writew(baud, uart_base + REG_BAUD);
> +       }
>
>         sbi_console_set_device(&shakti_console);
>
> diff --git a/lib/utils/serial/sifive-uart.c b/lib/utils/serial/sifive-uart.c
> index 7078611a5274..3581d47a6d4b 100644
> --- a/lib/utils/serial/sifive-uart.c
> +++ b/lib/utils/serial/sifive-uart.c
> @@ -97,7 +97,7 @@ int sifive_uart_init(unsigned long base, u32 in_freq, u32 baudrate)
>         uart_baudrate = baudrate;
>
>         /* Configure baudrate */
> -       if (in_freq)
> +       if (in_freq && baudrate)
>                 set_reg(UART_REG_DIV, uart_min_clk_divisor(in_freq, baudrate));
>
>         /* Disable interrupts */
> diff --git a/lib/utils/serial/uart8250.c b/lib/utils/serial/uart8250.c
> index 38ea11af4d31..99bf1bf733f2 100644
> --- a/lib/utils/serial/uart8250.c
> +++ b/lib/utils/serial/uart8250.c
> @@ -93,7 +93,7 @@ static struct sbi_console_device uart8250_console = {
>  int uart8250_init(unsigned long base, u32 in_freq, u32 baudrate, u32 reg_shift,
>                   u32 reg_width, u32 reg_offset)
>  {
> -       u16 bdiv;
> +       u16 bdiv = 0;
>
>         uart8250_base      = (volatile char *)base + reg_offset;
>         uart8250_reg_shift = reg_shift;
> @@ -101,7 +101,10 @@ int uart8250_init(unsigned long base, u32 in_freq, u32 baudrate, u32 reg_shift,
>         uart8250_in_freq   = in_freq;
>         uart8250_baudrate  = baudrate;
>
> -       bdiv = (uart8250_in_freq + 8 * uart8250_baudrate) / (16 * uart8250_baudrate);
> +       if (uart8250_baudrate) {
> +               bdiv = (uart8250_in_freq + 8 * uart8250_baudrate) /
> +                      (16 * uart8250_baudrate);
> +       }
>
>         /* Disable all interrupts */
>         set_reg(UART_IER_OFFSET, 0x00);
> --
> 2.36.1
>
>
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