On Wed, 2018-03-14 at 20:04 -0600, Daniel Kurtz wrote: > The old_serial_port global array in 8250_core is supposed to hold an > entry > for each serial port on the system that cannot be discovered via a > standard enumeration mechanism (aka ACPI/PCI/DTS). The array is > populated > at compile-time from the value specified in the SERIAL_PORT_DFNS > macro. > This macro is defined in arch/serial.h. > > For x86, this macro is currently unconditionally initialized to supply > four ioport UARTs (0x3F8, 0x2F8, 0x3E8, 0x2E8). > > However, not all x86 CPUs have these four ioport UARTs. For example, > the > UARTs on AMD Carrizo and later are separate memory mapped Designware > IP > blocks. > > Fairly early in boot the console_initcall univ8250_console_init > iterates > over this array and installs these old UARTs into the global array > serial8250_ports. Further, it attempts to register them for use as > the console. In other words, if, for example, the kernel commandline > has > console=ttyS0, the console will be switched over to one of these > non-existent UARTs. Only later, when the real UART drivers are probed > and their devices are instantiated will the console switch back over > to > the proper UART. > > This is noticeable when using earlycon, since part of the serial > console > log will appear to disappear (when the bogus old takes over) and then > re-appear (when the real UART finally gets registered for the > console). > > The problem is even more noticable when *not* using earlycon, since in > this case the entire console output is missing, having been > incorrectly > played back to the non-existing serial port. > > Create a global variable to allow skipping old serial port > initialization > and wire it up to the AMDCZ ACPI SPCR quirk and the special amdcz > earlycon > setup handler. I don't like this approach at all. But unfortunately I have nothing to propose. Just felt like I have to share my opinion on this. -- Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> Intel Finland Oy -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
