On Thu, Mar 1, 2018 at 9:22 PM, Daniel Kurtz <djkurtz@xxxxxxxxxxxx> wrote: > On Thu, Mar 1, 2018 at 11:47 AM Andy Shevchenko <andy.shevchenko@xxxxxxxxx> > wrote: > "earlycon simply does not utilize the information". > > earlycon parses iotype, mapbase and baud (from options). However, it is > hard-coded to assume that the clock used to generate the UART bitclock is > always "BASE_BAUD * 16" (1843200). While this may be true for many UARTs, > it isn't true for AMD's CZ/ST which has a 8250_dw and uses a fixed 48 MHz > clock. The main 8250_dw driver uses devm_clk_get to get the "baudclk" and > uses its rate to initialize uartclk. For AMD CZ/ST, this "baudclk" is > actually a set up in acpi_apd.c when there is an acpi match for "AMD0020", > with a rate read from the .fixed_clk_rate param of the corresponding > apd_device_desc. > > This patch attempts to add a way to inform earlycon about this clock. As > noted above, the information is actually already in the kernel and used by > 8250_dw - I would happy be to hear recommendations for wiring this data > into earlycon that doesn't require adding another command line arg. And it should not require that for sure! I would look to this later. It's late here. I need to do a bit of research for the answer. > I see that support was also added recently to earlycon to let it use ACPI > SPCR to choose a console and configure its parameters... but AFAICT, this > path also doesn't allow specifying the uart clock. Fix your firmware then. It should set console to 115200 like (almost) everyone does. Okay, configures a necessary IPs to feed UART with expected 1.8432M clock. -- With Best Regards, Andy Shevchenko -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
