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Add device links after the devices are created (but before they are probed) by looking at common DT bindings like clocks and interconnects. Automatically adding device links for functional dependencies at the framework level provides the following benefits: - Optimizes device probe order and avoids the useless work of attempting probes of devices that will not probe successfully (because their suppliers aren't present or haven't probed yet). For example, in a commonly available mobile SoC, registering just one consumer device's driver at an initcall level earlier than the supplier device's driver causes 11 failed probe attempts before the consumer device probes successfully. This was with a kernel with all the drivers statically compiled in. This problem gets a lot worse if all the drivers are loaded as modules without direct symbol dependencies. - Supplier devices like clock providers, interconnect providers, etc need to keep the resources they provide active and at a particular state(s) during boot up even if their current set of consumers don't request the resource to be active. This is because the rest of the consumers might not have probed yet and turning off the resource before all the consumers have probed could lead to a hang or undesired user experience. Some frameworks (Eg: regulator) handle this today by turning off "unused" resources at late_initcall_sync and hoping all the devices have probed by then. This is not a valid assumption for systems with loadable modules. Other frameworks (Eg: clock) just don't handle this due to the lack of a clear signal for when they can turn off resources. This leads to downstream hacks to handle cases like this that can easily be solved in the upstream kernel. By linking devices before they are probed, we give suppliers a clear count of the number of dependent consumers. Once all of the consumers are active, the suppliers can turn off the unused resources without making assumptions about the number of consumers. By default we just add device-links to track "driver presence" (probe succeeded) of the supplier device. If any other functionality provided by device-links are needed, it is left to the consumer/supplier devices to change the link when they probe. kbuild test robot reported clang error about missing const Reported-by: kbuild test robot <lkp@intel.com> Signed-off-by: Saravana Kannan <saravanak@google.com> Link: https://lore.kernel.org/r/20190904211126.47518-4-saravanak@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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8.1 KiB
ReStructuredText
214 lines
8.1 KiB
ReStructuredText
.. _kernelparameters:
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The kernel's command-line parameters
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====================================
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The following is a consolidated list of the kernel parameters as
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implemented by the __setup(), core_param() and module_param() macros
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and sorted into English Dictionary order (defined as ignoring all
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punctuation and sorting digits before letters in a case insensitive
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manner), and with descriptions where known.
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The kernel parses parameters from the kernel command line up to "``--``";
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if it doesn't recognize a parameter and it doesn't contain a '.', the
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parameter gets passed to init: parameters with '=' go into init's
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environment, others are passed as command line arguments to init.
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Everything after "``--``" is passed as an argument to init.
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Module parameters can be specified in two ways: via the kernel command
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line with a module name prefix, or via modprobe, e.g.::
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(kernel command line) usbcore.blinkenlights=1
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(modprobe command line) modprobe usbcore blinkenlights=1
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Parameters for modules which are built into the kernel need to be
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specified on the kernel command line. modprobe looks through the
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kernel command line (/proc/cmdline) and collects module parameters
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when it loads a module, so the kernel command line can be used for
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loadable modules too.
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Hyphens (dashes) and underscores are equivalent in parameter names, so::
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log_buf_len=1M print-fatal-signals=1
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can also be entered as::
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log-buf-len=1M print_fatal_signals=1
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Double-quotes can be used to protect spaces in values, e.g.::
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param="spaces in here"
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cpu lists:
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----------
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Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,
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nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
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<cpu number>,...,<cpu number>
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or
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<cpu number>-<cpu number>
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(must be a positive range in ascending order)
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or a mixture
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<cpu number>,...,<cpu number>-<cpu number>
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Note that for the special case of a range one can split the range into equal
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sized groups and for each group use some amount from the beginning of that
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group:
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<cpu number>-cpu number>:<used size>/<group size>
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For example one can add to the command line following parameter:
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isolcpus=1,2,10-20,100-2000:2/25
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where the final item represents CPUs 100,101,125,126,150,151,...
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This document may not be entirely up to date and comprehensive. The command
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"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
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module. Loadable modules, after being loaded into the running kernel, also
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reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
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parameters may be changed at runtime by the command
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``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
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The parameters listed below are only valid if certain kernel build options were
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enabled and if respective hardware is present. The text in square brackets at
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the beginning of each description states the restrictions within which a
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parameter is applicable::
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ACPI ACPI support is enabled.
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AGP AGP (Accelerated Graphics Port) is enabled.
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ALSA ALSA sound support is enabled.
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APIC APIC support is enabled.
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APM Advanced Power Management support is enabled.
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ARM ARM architecture is enabled.
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ARM64 ARM64 architecture is enabled.
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AX25 Appropriate AX.25 support is enabled.
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CLK Common clock infrastructure is enabled.
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CMA Contiguous Memory Area support is enabled.
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DRM Direct Rendering Management support is enabled.
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DYNAMIC_DEBUG Build in debug messages and enable them at runtime
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EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
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EFI EFI Partitioning (GPT) is enabled
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EIDE EIDE/ATAPI support is enabled.
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EVM Extended Verification Module
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FB The frame buffer device is enabled.
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FTRACE Function tracing enabled.
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GCOV GCOV profiling is enabled.
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HW Appropriate hardware is enabled.
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IA-64 IA-64 architecture is enabled.
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IMA Integrity measurement architecture is enabled.
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IOSCHED More than one I/O scheduler is enabled.
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IP_PNP IP DHCP, BOOTP, or RARP is enabled.
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IPV6 IPv6 support is enabled.
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ISAPNP ISA PnP code is enabled.
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ISDN Appropriate ISDN support is enabled.
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ISOL CPU Isolation is enabled.
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JOY Appropriate joystick support is enabled.
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KGDB Kernel debugger support is enabled.
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KVM Kernel Virtual Machine support is enabled.
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LIBATA Libata driver is enabled
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LP Printer support is enabled.
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LOOP Loopback device support is enabled.
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M68k M68k architecture is enabled.
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These options have more detailed description inside of
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Documentation/m68k/kernel-options.rst.
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MDA MDA console support is enabled.
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MIPS MIPS architecture is enabled.
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MOUSE Appropriate mouse support is enabled.
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MSI Message Signaled Interrupts (PCI).
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MTD MTD (Memory Technology Device) support is enabled.
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NET Appropriate network support is enabled.
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NUMA NUMA support is enabled.
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NFS Appropriate NFS support is enabled.
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OF Devicetree is enabled.
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OSS OSS sound support is enabled.
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PV_OPS A paravirtualized kernel is enabled.
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PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
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PARISC The PA-RISC architecture is enabled.
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PCI PCI bus support is enabled.
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PCIE PCI Express support is enabled.
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PCMCIA The PCMCIA subsystem is enabled.
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PNP Plug & Play support is enabled.
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PPC PowerPC architecture is enabled.
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PPT Parallel port support is enabled.
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PS2 Appropriate PS/2 support is enabled.
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RAM RAM disk support is enabled.
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RDT Intel Resource Director Technology.
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S390 S390 architecture is enabled.
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SCSI Appropriate SCSI support is enabled.
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A lot of drivers have their options described inside
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the Documentation/scsi/ sub-directory.
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SECURITY Different security models are enabled.
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SELINUX SELinux support is enabled.
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APPARMOR AppArmor support is enabled.
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SERIAL Serial support is enabled.
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SH SuperH architecture is enabled.
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SMP The kernel is an SMP kernel.
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SPARC Sparc architecture is enabled.
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SWSUSP Software suspend (hibernation) is enabled.
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SUSPEND System suspend states are enabled.
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TPM TPM drivers are enabled.
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TS Appropriate touchscreen support is enabled.
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UMS USB Mass Storage support is enabled.
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USB USB support is enabled.
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USBHID USB Human Interface Device support is enabled.
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V4L Video For Linux support is enabled.
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VMMIO Driver for memory mapped virtio devices is enabled.
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VGA The VGA console has been enabled.
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VT Virtual terminal support is enabled.
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WDT Watchdog support is enabled.
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XT IBM PC/XT MFM hard disk support is enabled.
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X86-32 X86-32, aka i386 architecture is enabled.
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X86-64 X86-64 architecture is enabled.
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More X86-64 boot options can be found in
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Documentation/x86/x86_64/boot-options.rst.
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X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
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X86_UV SGI UV support is enabled.
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XEN Xen support is enabled
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In addition, the following text indicates that the option::
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BUGS= Relates to possible processor bugs on the said processor.
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KNL Is a kernel start-up parameter.
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BOOT Is a boot loader parameter.
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Parameters denoted with BOOT are actually interpreted by the boot
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loader, and have no meaning to the kernel directly.
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Do not modify the syntax of boot loader parameters without extreme
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need or coordination with <Documentation/x86/boot.rst>.
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There are also arch-specific kernel-parameters not documented here.
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See for example <Documentation/x86/x86_64/boot-options.rst>.
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Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
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a trailing = on the name of any parameter states that that parameter will
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be entered as an environment variable, whereas its absence indicates that
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it will appear as a kernel argument readable via /proc/cmdline by programs
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running once the system is up.
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The number of kernel parameters is not limited, but the length of the
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complete command line (parameters including spaces etc.) is limited to
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a fixed number of characters. This limit depends on the architecture
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and is between 256 and 4096 characters. It is defined in the file
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./include/asm/setup.h as COMMAND_LINE_SIZE.
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Finally, the [KMG] suffix is commonly described after a number of kernel
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parameter values. These 'K', 'M', and 'G' letters represent the _binary_
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multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30
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bytes respectively. Such letter suffixes can also be entirely omitted:
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.. include:: kernel-parameters.txt
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:literal:
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Todo
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----
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Add more DRM drivers.
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