Messages in this thread | | | Subject | Re: [PATCH 2/2] x86/Kconfig: Add config to allow not defining old serial ports | From | Randy Dunlap <> | Date | Wed, 7 Mar 2018 17:49:14 -0800 |
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On 03/07/2018 03:24 PM, 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 attemptes 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 most 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). > > Add a Kconfig option to allow overriding this default hard coded value > for arch/x86 devices that do not have such serial ports. > > Signed-off-by: Daniel Kurtz <djkurtz@chromium.org> > --- > arch/x86/Kconfig | 11 +++++++++++ > arch/x86/include/asm/serial.h | 4 ++++ > 2 files changed, 15 insertions(+) > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index 0a258bb30159..7501cd776cfc 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -463,6 +463,17 @@ config X86_SERIAL_BASE_BAUD > default, but may need to be changed to get earlycon to work on > some hardware, such as those that use AMD Carrizo or later SoCs. > > +config X86_SERIAL_DEFINE_OLD_SERIAL_PORTS > + bool "Define un-enumerable serial ports" > + default y > + help > + Say Y here if you want the kernel to assume the precense of built-in
presence
> + serial ports that do not have a standard enumeration mechanism. > + Platforms that can find all serial ports via mechanisms like ACPI or > + PCI can set this to N. > + > + If unsure, say Y. > + > if X86_32 > config X86_BIGSMP > bool "Support for big SMP systems with more than 8 CPUs"
-- ~Randy
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