On Thu, Mar 1, 2018 at 8:20 PM, Daniel Kurtz <djkurtz@xxxxxxxxxxxx> 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. It needs to be discussed. First of all, if you are going to do this you need to add a parse of human readable formats (IIRC kernel has helpers), i.e. "48M", "38.4M" and so on. Next, I was under impression that purpose of earlycon (in difference to earlyprintk) is to re-use existing drivers as fully as possible. So, what exactly happens in your case? Are your driver lacks of properly set clock? Or earlycon does simple not utilizing this information? -- With Best Regards, Andy Shevchenko -- 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
