On 03/01/2018 10:20 AM, Daniel Kurtz wrote:
> Currently when an earlycon is registered, the uartclk is assumed to be
> BASE_BAUD * 16 = 1843200. If a baud rate is specified in the earlycon
> options, then 8250_early's init_port will program the UART clock divider
> registers based on this assumed uartclk.
>
> However, not all uarts have a UART clock of 1843200. For example, the
> 8250_dw uart in AMD's CZ/ST uses a fixed 48 MHz clock (as specified in
> cz_uart_desc in acpi_apd.c). Thus, specifying a baud when using earlycon
> on such a device will result in incorrect divider values and a wrong UART
> clock.
>
> Fix this by extending the earlycon options parameter to allow specification
> of a uartclk, like so:
>
> earlycon=uart,mmio32,0xfedc6000,115200,48000000
>
> If none is specified, fall-back to prior behavior - 1843200.
>
> Signed-off-by: Daniel Kurtz <djkurtz@xxxxxxxxxxxx>
Hi,
Hopefully there will also be an update to one of
Documentation/admin-guide/kernel-parameters.txt or
Documentation/admin-guide/serial-console.rst.
Thanks.
> ---
> drivers/tty/serial/earlycon.c | 8 ++++++--
> include/linux/serial_core.h | 2 +-
> 2 files changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
> index 870e84fb6e39..c9b38f520057 100644
> --- a/drivers/tty/serial/earlycon.c
> +++ b/drivers/tty/serial/earlycon.c
> @@ -115,12 +115,17 @@ static int __init parse_options(struct earlycon_device *device, char *options)
> }
>
> if (options) {
> - device->baud = simple_strtoul(options, NULL, 0);
> + char *uartclk;
> + device->baud = simple_strtoul(options, &uartclk, 0);
> + if (*uartclk++ == ',')
> + port->uartclk = simple_strtoul(uartclk, NULL, 0);
> length = min(strcspn(options, " ") + 1,
> (size_t)(sizeof(device->options)));
> strlcpy(device->options, options, length);
> }
>
> + port->uartclk = (port->uartclk) ?: BASE_BAUD * 16;
> +
> return 0;
> }
>
> @@ -134,7 +139,6 @@ static int __init register_earlycon(char *buf, const struct earlycon_id *match)
> buf = NULL;
>
> spin_lock_init(&port->lock);
> - port->uartclk = BASE_BAUD * 16;
> if (port->mapbase)
> port->membase = earlycon_map(port->mapbase, 64);
>
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index b32df49a3bd5..b772f0d20b18 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -343,7 +343,7 @@ static inline int uart_poll_timeout(struct uart_port *port)
> struct earlycon_device {
> struct console *con;
> struct uart_port port;
> - char options[16]; /* e.g., 115200n8 */
> + char options[32]; /* e.g., 115200n8,48000000 */
> unsigned int baud;
> };
>
>
--
~Randy
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