On Thu, Mar 15, 2018 at 7:04 AM Andy Shevchenko < andriy.shevchenko@xxxxxxxxxxxxxxx> wrote: > 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. I'm not very proud of this either, but I don't know how else to set this flag. I proposed a Kconfig option earlier, but that also met resistance. Perhaps another kernel command line option? > -- > Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > Intel Finland Oy -- 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
