Hi, I just spent few hours debugging hidden hw lockup and I need to
consult driver core code behaviour.
I have a BCM4908 SoC based board with a NAND controller on it.
### Hardware binding
Hardware details:
arch/arm64/boot/dts/broadcom/bcmbca/bcm4908.dtsi
Relevant part:
nand-controller@1800 {
compatible = "brcm,nand-bcm63138", "brcm,brcmnand-v7.1", "brcm,brcmnand";
reg = <0x1800 0x600>, <0x2000 0x10>;
reg-names = "nand", "nand-int-base";
}:
Above binding is based on the documentation:
Documentation/devicetree/bindings/mtd/brcm,brcmnand.yaml
### Linux drivers
Linux has separated drivers for few Broadcom's NAND controller bindings:
1. drivers/mtd/nand/raw/brcmnand/bcm63138_nand.c for:
brcm,nand-bcm63138
2. drivers/mtd/nand/raw/brcmnand/brcmnand.c for:
brcm,brcmnand-v2.1
brcm,brcmnand-v2.2
brcm,brcmnand-v4.0
brcm,brcmnand-v5.0
brcm,brcmnand-v6.0
brcm,brcmnand-v6.1
brcm,brcmnand-v6.2
brcm,brcmnand-v7.0
brcm,brcmnand-v7.1
brcm,brcmnand-v7.2
brcm,brcmnand-v7.3
3. drivers/mtd/nand/raw/brcmnand/brcmstb_nand.c for:
brcm,brcmnand
### Problem
As first Linux probes my hardware using the "brcm,nand-bcm63138"
compatibility string driver bcm63138_nand.c. That's good.
It that fails however (.probe() returns an error) then Linux core starts
probing using drivers for less specific bindings.
In my case probing with the "brcm,brcmnand" string driver brcmstb_nand.c
results in ignoring SoC specific bits and causes a hardware lockup. Hw
isn't initialized properly and writel_relaxed(0x00000009, base + 0x04)
just make it hang.
That obviously isn't an acceptable behavior for me. So I'm wondering
what's going on wrong here.
Should Linux avoid probing with less-specific compatible strings?
Or should I not claim hw to be "brcm,brcmnand" compatible if it REQUIRES
SoC-specific handling?
An extra note: that fallback probing happens even with .probe()
returning -EPROBE_DEFER. This actually smells fishy for me on the Linux
core part.
I'm not an expect but I think core should wait for actual error without
trying less-specific compatible strings & drivers.
