On Thu, Mar 1, 2018 at 11:47 AM Andy Shevchenko <andy.shevchenko@xxxxxxxxx> wrote: > On Thu, Mar 1, 2018 at 8:43 PM, Daniel Kurtz <djkurtz@xxxxxxxxxxxx> wrote: > Please, hold on with new versions. > I'm not satisfied (yet?) by the approach. Copying over your comment on v1: > It needs to be discussed. Sure. > 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? "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. 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. -Dan -- 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
