linux/drivers/tty/hvc/Kconfig
Shanker Donthineni 4419da5d5d tty: hvc: dcc: Bind driver to CPU core0 for reads and writes
Some external debuggers do not handle reads/writes from/to DCC
on secondary cores. Each core has its own DCC device registers,
so when a core reads or writes from/to DCC, it only accesses
its own DCC device. Since kernel code can run on any core,
every time the kernel wants to write to the console, it might
write to a different DCC.

In SMP mode, external debugger creates multiple windows, and
each window shows the DCC output only from that core's DCC.
The result is that console output is either lost or scattered
across windows.

Selecting this debug option will enable code that serializes all
console input and output to core 0. The DCC driver will create
input and output FIFOs that all cores will use. Reads and writes
from/to DCC are handled by a workqueue that runs only core 0.

This is a debug feature to be used only in early stage development
where debug serial console support would not be present. It disables
PM feature like CPU hotplug and is not suitable for production
environment.

Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
Acked-by: Adam Wallis <awallis@codeaurora.org>
Signed-off-by: Timur Tabi <timur@codeaurora.org>
Signed-off-by: Elliot Berman <eberman@codeaurora.org>
Signed-off-by: Sai Prakash Ranjan <quic_saipraka@quicinc.com>
Link: https://lore.kernel.org/r/20220428090858.14489-1-quic_saipraka@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2022-05-05 22:45:57 +02:00

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# SPDX-License-Identifier: GPL-2.0
config HVC_DRIVER
bool
help
Generic "hypervisor virtual console" infrastructure for various
hypervisors (pSeries, iSeries, Xen).
It will automatically be selected if one of the back-end console drivers
is selected.
config HVC_IRQ
bool
config HVC_CONSOLE
bool "pSeries Hypervisor Virtual Console support"
depends on PPC_PSERIES
select HVC_DRIVER
select HVC_IRQ
help
pSeries machines when partitioned support a hypervisor virtual
console. This driver allows each pSeries partition to have a console
which is accessed via the HMC.
config HVC_OLD_HVSI
bool "Old driver for pSeries serial port (/dev/hvsi*)"
depends on HVC_CONSOLE
config HVC_OPAL
bool "OPAL Console support"
depends on PPC_POWERNV
select HVC_DRIVER
select HVC_IRQ
default y
help
PowerNV machines running under OPAL need that driver to get a console
config HVC_RTAS
bool "IBM RTAS Console support"
depends on PPC_RTAS
select HVC_DRIVER
help
IBM Console device driver which makes use of RTAS
config HVC_IUCV
bool "z/VM IUCV Hypervisor console support (VM only)"
depends on S390 && NET
select HVC_DRIVER
select IUCV
default y
help
This driver provides a Hypervisor console (HVC) back-end to access
a Linux (console) terminal via a z/VM IUCV communication path.
config HVC_XEN
bool "Xen Hypervisor Console support"
depends on XEN
select HVC_DRIVER
select HVC_IRQ
default y
help
Xen virtual console device driver
config HVC_XEN_FRONTEND
bool "Xen Hypervisor Multiple Consoles support"
depends on HVC_XEN
select XEN_XENBUS_FRONTEND
default y
help
Xen driver for secondary virtual consoles
config HVC_UDBG
bool "udbg based fake hypervisor console"
depends on PPC
select HVC_DRIVER
help
This is meant to be used during HW bring up or debugging when
no other console mechanism exist but udbg, to get you a quick
console for userspace. Do NOT enable in production kernels.
config HVC_DCC
bool "ARM JTAG DCC console"
depends on ARM || ARM64
select HVC_DRIVER
select SERIAL_CORE_CONSOLE
help
This console uses the JTAG DCC on ARM to create a console under the HVC
driver. This console is used through a JTAG only on ARM. If you don't have
a JTAG then you probably don't want this option.
config HVC_DCC_SERIALIZE_SMP
bool "Use DCC only on CPU core 0"
depends on SMP && HVC_DCC
help
This is a DEBUG option to serialize all console input and output to CPU 0.
Some external debuggers, do not handle reads/writes from/to DCC on more
than one CPU core. Each core has its own DCC device registers, so when a
CPU core reads or writes from/to DCC, it only accesses its own DCC device.
Since kernel code can run on any CPU core, every time the kernel wants to
write to the console, it might write to a different DCC.
In SMP mode, external debuggers create multiple windows, and each window
shows the DCC output only from that core's DCC. The result is that
console output is either lost or scattered across windows.
Enable this option only if you are sure that you do not need features like
CPU hotplug to work. For example, during early chipset bringups without
debug serial console support. If unsure, say N.
config HVC_RISCV_SBI
bool "RISC-V SBI console support"
depends on RISCV_SBI_V01
select HVC_DRIVER
help
This enables support for console output via RISC-V SBI calls, which
is normally used only during boot to output printk.
If you don't know what do to here, say Y.
config HVCS
tristate "IBM Hypervisor Virtual Console Server support"
depends on PPC_PSERIES && HVC_CONSOLE
help
Partitionable IBM Power5 ppc64 machines allow hosting of
firmware virtual consoles from one Linux partition by
another Linux partition. This driver allows console data
from Linux partitions to be accessed through TTY device
interfaces in the device tree of a Linux partition running
this driver.
To compile this driver as a module, choose M here: the
module will be called hvcs. Additionally, this module
will depend on arch specific APIs exported from hvcserver.ko
which will also be compiled when this driver is built as a
module.