qconfig: Update the documentation
Update qconfig's documentation to better reflect its new purpose in life.
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/develop/qconfig.rst b/doc/develop/qconfig.rst
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+.. SPDX-License-Identifier: GPL-2.0+
+
+qconfig - Querying CONFIG options
+=================================
+
+It is not possible to see all the CONFIG options used by a board without
+building its `.config` file. This tool allows this to be done efficiently for
+all boards, or a subset, writing the results to a unified database file.
+
+This database can be queried, to find boards which used a certain combination
+of options, to aid in discovering Kconfig options which imply others.
+
+The tool also permits syncing of defconfigs, which corrects the ordering and
+drops options which are implied by others.
+
+Finally, it allows scanning the source code to look for inconsistencies in the
+use of Kconfig options.
+
+Installation
+------------
+
+You may need to install 'python3-asteval' for the 'asteval' module.
+
+How does it work?
+-----------------
+
+When building a database (`-b`), this tool runs configuration and builds
+include/autoconf.mk for every defconfig. The config options defined in Kconfig
+appear in the .config file (unless they are hidden because of unmet dependency.)
+On the other hand, the config options defined by board headers are seen
+in include/autoconf.mk.
+
+When resyncing defconfigs (`-s`) the .config is synced by "make savedefconfig"
+and the defconfig is updated with it.
+
+For faster processing, this tool is multi-threaded. It creates
+separate build directories where the out-of-tree build is run. The
+temporary build directories are automatically created and deleted as
+needed. The number of threads are chosen based on the number of the CPU
+cores of your system although you can change it via -j (--jobs) option.
+
+Note that `*.config` fragments are not supported.
+
+Toolchains
+----------
+
+Appropriate toolchains are necessary to generate include/autoconf.mk
+for all the architectures supported by U-Boot. Most of them are available
+at the kernel.org site. This tool uses the same tools as
+:doc:`../build/buildman`, so you can use `buildman --fetch-arch` to fetch
+toolchains.
+
+
+Examples
+--------
+
+To sync only X86 defconfigs::
+
+ ./tools/qconfig.py -s -d <(grep -l X86 configs/*)
+
+or::
+
+ grep -l X86 configs/* | ./tools/qconfig.py -s -d -
+
+To process CONFIG_CMD_FPGAD only for a subset of configs based on path match::
+
+ ls configs/{hrcon*,iocon*,strider*} | \
+ ./tools/qconfig.py -C CONFIG_CMD_FPGAD -d -
+
+
+Finding boards with particular CONFIG combinations
+--------------------------------------------------
+
+You can use `qconfig.py` to figure out which boards have a CONFIG enabled, or
+which do not. To use it, first build a database::
+
+ ./tools/qconfig.py -b
+
+Then you can run queries using the `-f` flag followed by a list of CONFIG terms.
+Each term is CONFIG name, with or without a tilde (~) prefix. The tool searches
+for boards which match the CONFIG name, or do not match if tilde is used. For
+example, to find boards which enabled CONFIG_SCSI but not CONFIG_BLK::
+
+ tools/qconfig.py -f SCSI ~BLK
+ 3 matches
+ pg_wcom_seli8_defconfig highbank_defconfig pg_wcom_expu1_defconfig
+
+
+Finding implied CONFIGs
+-----------------------
+
+Some CONFIG options can be implied by others and this can help to reduce
+the size of the defconfig files. For example, CONFIG_X86 implies
+CONFIG_CMD_IRQ, so we can put 'imply CMD_IRQ' under 'config X86' and
+all x86 boards will have that option, avoiding adding CONFIG_CMD_IRQ to
+each of the x86 defconfig files.
+
+This tool can help find such configs. To use it, first build a database::
+
+ ./tools/qconfig.py -b
+
+Then try to query it::
+
+ ./tools/qconfig.py -i CONFIG_I8042_KEYB
+ CONFIG_I8042_KEYB found in 33/5155 defconfigs
+ 28 : CONFIG_X86
+ 28 : CONFIG_SA_PCIEX_LENGTH
+ 28 : CONFIG_HPET_ADDRESS
+ 28 : CONFIG_MAX_PIRQ_LINKS
+ 28 : CONFIG_I8254_TIMER
+ 28 : CONFIG_I8259_PIC
+ 28 : CONFIG_RAMBASE
+ 28 : CONFIG_IRQ_SLOT_COUNT
+ 28 : CONFIG_PCIE_ECAM_SIZE
+ 28 : CONFIG_APIC
+ ...
+
+This shows a list of config options which might imply CONFIG_I8042_KEYB along
+with how many defconfigs they cover. From this you can see that CONFIG_X86
+generally implies CONFIG_I8042_KEYB but not always (28 out of 35). Therefore,
+instead of adding CONFIG_I8042_KEYB to
+the defconfig of every x86 board, you could add a single imply line to the
+Kconfig file::
+
+ config X86
+ bool "x86 architecture"
+ ...
+ imply CMD_EEPROM
+
+That will cover 28 defconfigs and you can perhaps find another condition that
+indicates that CONFIG_I8042_KEYB is not needed for the remaining 5 boards. Many
+of the options listed are not suitable as they are not related. E.g. it would be
+odd for CONFIG_RAMBASE to imply CONFIG_I8042_KEYB.
+
+Using this search you can reduce the size of qconfig patches.
+
+You can automatically add 'imply' statements in the Kconfig with the -a
+option::
+
+ ./tools/qconfig.py -s -i CONFIG_SCSI \
+ -a CONFIG_ARCH_LS1021A,CONFIG_ARCH_LS1043A
+
+This will add 'imply SCSI' to the two CONFIG options mentioned, assuming that
+the database indicates that they do actually imply CONFIG_SCSI and do not
+already have an 'imply SCSI'.
+
+The output shows where the imply is added::
+
+ 18 : CONFIG_ARCH_LS1021A arch/arm/cpu/armv7/ls102xa/Kconfig:1
+ 13 : CONFIG_ARCH_LS1043A arch/arm/cpu/armv8/fsl-layerscape/Kconfig:11
+ 12 : CONFIG_ARCH_LS1046A arch/arm/cpu/armv8/fsl-layerscape/Kconfig:31
+
+The first number is the number of boards which can avoid having a special
+CONFIG_SCSI option in their defconfig file if this 'imply' is added.
+The location at the right is the Kconfig file and line number where the config
+appears. For example, adding 'imply CONFIG_SCSI' to the 'config ARCH_LS1021A'
+in arch/arm/cpu/armv7/ls102xa/Kconfig at line 1 will help 18 boards to reduce
+the size of their defconfig files.
+
+If you want to add an 'imply' to every imply config in the list, you can use::
+
+ ./tools/qconfig.py -s -i CONFIG_SCSI -a all
+
+To control which ones are displayed, use -I <list> where list is a list of
+options (use '-I help' to see possible options and their meaning).
+
+To skip showing you options that already have an 'imply' attached, use -A.
+
+When you have finished adding 'imply' options you can regenerate the
+defconfig files for affected boards with something like::
+
+ git show --stat | ./tools/qconfig.py -s -d -
+
+This will regenerate only those defconfigs changed in the current commit.
+If you start with (say) 100 defconfigs being changed in the commit, and add
+a few 'imply' options as above, then regenerate, hopefully you can reduce the
+number of defconfigs changed in the commit.
+
+
+Available options
+-----------------
+
+ --nocolour
+ Disables colouring of output. This is normally used when writing to a
+ terminal.
+
+ -C, --commit
+ Create a git commit with the changes when the operation is complete. A
+ standard commit message is used which may need to be edited.
+
+ -d, --defconfigs
+ Specify a file containing a list of defconfigs to move. The defconfig
+ files can be given with shell-style wildcards. Use '-' to read from stdin.
+
+ -f, --find
+ Find boards with a given config combination
+
+ -n, --dry-run
+ Perform a trial run that does not make any changes. It is useful to
+ see what is going to happen before one actually runs it.
+
+ -e, --exit-on-error
+ Exit immediately if Make exits with a non-zero status while processing
+ a defconfig file.
+
+ -s, --force-sync
+ Do "make savedefconfig" forcibly for all the defconfig files.
+ If not specified, "make savedefconfig" only occurs for cases
+ where at least one CONFIG was moved.
+
+ -S, --spl
+ Look for moved config options in spl/include/autoconf.mk instead of
+ include/autoconf.mk. This is useful for moving options for SPL build
+ because SPL related options (mostly prefixed with CONFIG_SPL\_) are
+ sometimes blocked by CONFIG_SPL_BUILD ifdef conditionals.
+
+ -j, --jobs
+ Specify the number of threads to run simultaneously. If not specified,
+ the number of threads is the same as the number of CPU cores.
+
+ -r, --git-ref
+ Specify the git ref to clone for building the autoconf.mk. If unspecified
+ use the CWD. This is useful for when changes to the Kconfig affect the
+ default values and you want to capture the state of the defconfig from
+ before that change was in effect. If in doubt, specify a ref pre-Kconfig
+ changes (use HEAD if Kconfig changes are not committed). Worst case it will
+ take a bit longer to run, but will always do the right thing.
+
+ -v, --verbose
+ Show any build errors as boards are built
+
+To see the complete list of supported options, run::
+
+ tools/qconfig.py -h