On Mon, 4 Dec 2023, Dawei Li wrote:
> DW apb uart databook defines couples of configuration parameters of
> dw8250 IP, among which there are 2 of them:
> - ADDTIONAL_FEATURE
> " Configure the peripheral to have the option to include FIFO status
> registers, shadow registers and encoded parameter register. Also
> configures the peripheral to have UART component version and the
> peripheral ID registers. "
>
> - FRACTIONAL_BAUD_DIVISOR_EN
> " Configures the peripheral to have Fractional Baud Rate Divisor.
> .... "
>
> These two parameters are completely irrelevant, and supposed to be
> independent of each other. However, in current dw8250 driver
> implementation, they are hooked together.
>
> The bug was hit when we are bringing up dw8250 IP on our hardware
> platform, in which parameters are configured in such combination:
> - ADDTIONAL_FEATURE disabled;
> - FRACTIONAL_BAUD_DIVISOR_EN enabled;
>
> Fixes: 701c5e73b296 ("serial: 8250_dw: add fractional divisor support")
> Cc: stable@xxxxxxxxxx
> Signed-off-by: Dawei Li <dawei.li@xxxxxxxxxxxx>
> ---
> drivers/tty/serial/8250/8250_dwlib.c | 22 +++++++++++-----------
> 1 file changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250_dwlib.c b/drivers/tty/serial/8250/8250_dwlib.c
> index 84843e204a5e..136ad093c5b6 100644
> --- a/drivers/tty/serial/8250/8250_dwlib.c
> +++ b/drivers/tty/serial/8250/8250_dwlib.c
> @@ -259,17 +259,6 @@ void dw8250_setup_port(struct uart_port *p)
> }
> up->capabilities |= UART_CAP_NOTEMT;
>
> - /*
> - * If the Component Version Register returns zero, we know that
> - * ADDITIONAL_FEATURES are not enabled. No need to go any further.
> - */
> - reg = dw8250_readl_ext(p, DW_UART_UCV);
> - if (!reg)
> - return;
> -
> - dev_dbg(p->dev, "Designware UART version %c.%c%c\n",
> - (reg >> 24) & 0xff, (reg >> 16) & 0xff, (reg >> 8) & 0xff);
> -
> /* Preserve value written by firmware or bootloader */
> old_dlf = dw8250_readl_ext(p, DW_UART_DLF);
> dw8250_writel_ext(p, DW_UART_DLF, ~0U);
> @@ -282,6 +271,17 @@ void dw8250_setup_port(struct uart_port *p)
> p->set_divisor = dw8250_set_divisor;
> }
>
> + /*
> + * If the Component Version Register returns zero, we know that
> + * ADDITIONAL_FEATURES are not enabled. No need to go any further.
> + */
> + reg = dw8250_readl_ext(p, DW_UART_UCV);
> + if (!reg)
> + return;
> +
> + dev_dbg(p->dev, "Designware UART version %c.%c%c\n",
> + (reg >> 24) & 0xff, (reg >> 16) & 0xff, (reg >> 8) & 0xff);
> +
> reg = dw8250_readl_ext(p, DW_UART_CPR);
> if (!reg) {
> reg = data->pdata->cpr_val;
>
The very same code change is already in tty-next (from another author).
--
i.
