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 <[email protected]> --- 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; }; -- 2.16.2.395.g2e18187dfd-goog
