On Thu, Mar 01, 2018 at 10:30:45AM -0800, Randy Dunlap wrote: > 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. Well, considering I'm not taking this patch unless it comes with such an update, I'm hoping as well :) greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
