I'm interested in compiling a custom kernel for the pi. I have the source from the github archive, which includes a make target for a default configuration:
make ARCH=arm bcmrpi_defconfig
But (as with normal linux distro kernels) this includes a lot of stuff I will never need, and some things that I'd like to change.
What are the options that are actually required to make various common pi-centric things work?
Starting with the default configuration, or one you know works already, is a good idea. Beware that for the Pi 2, you should use:
make bcm2709_defconfig
Instead of bcmrpi_defconfig.
Note that if you want to avoid clobbering an existing kernel install of the same version, set the General setup -> Local version - append to kernel release string to a unique value.
I've used the actual labels from .config here, sans CONFIG_; if you are using e.g., make menuconfig, you can find the relevant option with the search (forward slash /). These labels are also used at the top of the "Help" page for each option. Note that the term enable(d) refers to something which causes an option to appear, distinct from actually selecting the option to be built.
Where there are differences between the A/B/B+/A+ boards and the Pi 2, this is indicated. In some places this is the difference between the Broadcom 2708 and 2709 families, but in other places, the Pi 2 uses the same 2708 (or 2835) option as the other boards.
For A/A+/B/B+:
For Pi 2:
Kernel Memory Split:
Because of problems with a couple of pieces of legacy software, the default config may use 3G/1G here which will leave 25% of the Pi 2's RAM unavailable to user space. If you are concerned about this, check Kernel Features -> Memory Split.
These can't be modules, obviously, since they are needed to access /lib/modules; they must be built-in. They're in the "Device Drivers" section of menuconfig.
Since the root partition is usually ext formatted, you also want that built in:
The boot partition is vfat, so:
These are various things you (almost certainly) need, so I've listed them first.
For keyboards and mice:
For hard drives:
For tethering Android devices, see my answer here.
USB must be enabled first.
NET (Networking support), a top level option; inside that are:
NETDEVICES (Network device support) in "Device Drivers", then:
To enable the onboard sound:
There's nothing further required for X server support; there are no DRI driver options for the pi's SoC.
If you want to use the framebuffer, which allows applications such as fbi and omxplayer to display graphics outside of X:
If you do this and you want the penguin (or rather, the raspberry) on the boot console, remember LOGO (Bootup logo) under Graphics Support.
You may also want to look at options under System Type -> Broadcom2708 (or 9) Implementations.
/sys/class/gpio interface.You have a choice here; if you try to choose both, the first one will be cancelled (although you can build one as a module, change the config, build the other, and use them both if you really want to).
/sys/devices/platform/bcm2835_hwmon -- temp1_input and temp1_max. The former is the same /sys/devices/virtual/thermal/thermal_zone0/temp; the latter is always 85000 (i.e. 85 °C)./sys/class/devices/virtual/thermal/thermal_zone0 which includes temp and trip_point_0_temp (the same as temp1_max, above). Various userspace monitors will probably prefer this and may not work without it.A comment to goldilock's great post:
Just wanted to add one thing I observe with rpi-4.1.y branch (05376fce25aaab4f47182a5af04928bfa06f30d6): In order to have USB working (this includes the USB-connected ethernet), one has to also enable BCM2708_MBOX (Device Drivers->Mailbox Hardware Support->Broadcom BCM2708 Mailbox (vcio)).
Without this option USB starts initializing but only produces a bunch of scary messages like:
[ 1.193854] WARN::dwc_otg_core_reset:5109: dwc_otg_core_reset() HANG! Soft Reset GRSTCTL=80000001
[ 1.441137] WARN::dwc_otg_hcd_init:1047: FIQ DMA bounce buffers: virt = 0x9fc0c000 dma = 0x5d5e4000 len=9024
Btw. BCM2708_MBOX is also a prerequisite for THERMAL_BCM2835 and for SND_BCM2835.
In addition for video support, it looks like you need to enable:
Device Drivers ->
DMA Engine support ->
BCM2835 DMA engine support (CONFIG_DMA_BCM2835)
In order to load framebuffer driver correctly. You can enable it without DMA enabled, but it will fail to load.
In order to have Integrated Wireless (RPi 3 and Pi Zero W), you need to select the following:
Networking support ->
Wireless ->
cfg80211 - wireless configuration API (CONFIG_CFG80211)
Device Drivers ->
Network device support ->
Wireless LAN ->
Broadcom IEEE802.11n embedded FullMAC WLAN driver (CONFIG_BRCMFMAC)
Might be old, but I got here using the search. For the SDHC card you additionally need
Device Drivers ->
-> MMC block device driver )CONFIG_MMC_BLOCK)
otherwise your kernel will detect the SDHC card, but no partitions on it.
