Probing devices by their less-specific "compatible" bindings (here: brcmnand)

Krzysztof Kozlowski krzysztof.kozlowski at
Fri Mar 17 07:34:44 PDT 2023

On 17/03/2023 11:02, Rafał Miłecki wrote:
> 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 at 1800 {
> 	compatible = "brcm,nand-bcm63138", "brcm,brcmnand-v7.1", "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?

Why? If less-specific compatible is there, it means device is compatible
with it and it should work.

> Or should I not claim hw to be "brcm,brcmnand" compatible if it REQUIRES
> SoC-specific handling?

As you pointed this compatible does not work for your device, so they
are not compatible.

Best regards,

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