On Mon, Dec 21, 2020 at 7:47 AM Vincent Pelletier <plr.vincent@xxxxxxxxx> wrote: > > Hello, > > Distro: https://raspi.debian.net/ (sid) > Hardware: Raspberry Pi Zero W > Kernel version: 5.9.11 (linux-image-5.9.0-4-rpi) > > To access a device connected to my pi, I need the spi0 bus, and would > like to not be doing GPIO bit-banging when there are perfectly good > spi modules capable of using the SPI alternative mode of these pins. > > spi0 is declared in the vanilla devicetree for this device: > arch/arm/boot/dts/bcm2835-rpi-zero-w.dts ends up including > arch/arm/boot/dts/bcm283x.dtsi which contains: > spi: spi@7e204000 { > compatible = "brcm,bcm2835-spi"; > reg = <0x7e204000 0x200>; > interrupts = <2 22>; > clocks = <&clocks BCM2835_CLOCK_VPU>; > #address-cells = <1>; > #size-cells = <0>; > status = "disabled"; > }; > To my new-to-devicetree eye, this looks like this is intended to be > overridden, at least with a > status = "okay"; > property (although a bit more is needed). > As I believe is the correct way, I wrote a devicetree overlay doing > this and a bit more in order to enable this bus and one of its device > (the one matching the chip-select monitored by the board I connected). > > To confirm that I had no typo in my symbol names I ran fdtoverlay with > the packaged device tree binary, plus my overlay, but could not get it > to work, until I took a closer look at the packaged device tree and > realised it lacks a __symbols__ section. > So I pulled the source, added "-@" to the cmd_dtc rule in > scripts/Makefile.lib, built the dtb, tested fdtoverlay against it and > voila, it worked. I could then reboot with this devicetree, load my > overlay and use spi0 with no further change. > > So now I wonder why this option is not enabled while there are these > sections which seem to not be usable without an overlay ? > And further, why it does not seem to be possible to enable with a > kernel config option ? > > I must be missing something obvious, but I'm still failing to see it. Read the last time this came up: https://lore.kernel.org/linux-devicetree/71fb0ff289e84c55bd92ecd96bc9aa76@xxxxxxxxxxxxxxxxxxxxx/
