linux-kernel - Re: [PATCH v2] Support conditional deps using "depends on X if Y"

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Message-ID: <q490r0s5-q431-0335-n367-qrr05oos17s5@syhkavp.arg>
Date: Fri, 5 Dec 2025 11:14:34 -0500 (EST)
From: Nicolas Pitre <nico@...xnic.net>
To: Arnd Bergmann <arnd@...db.de>
cc: Nathan Chancellor <nathan@...nel.org>, 
    Graham Roff <grahamr@....qualcomm.com>, Nicolas Schier <nsc@...nel.org>, 
    Jonathan Corbet <corbet@....net>, linux-kbuild@...r.kernel.org, 
    linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Support conditional deps using "depends on X if Y"

On Fri, 5 Dec 2025, Arnd Bergmann wrote:

> On Fri, Dec 5, 2025, at 02:53, Nathan Chancellor wrote:
> > On Tue, Nov 18, 2025 at 10:46:51AM -0800, Graham Roff wrote:
> >>
> >> arch/arm64/Kconfig:
> >>   depends on ARM64_64K_PAGES || !ARM64_VA_BITS_52 -->
> >>   depends on ARM64_64K_PAGES if ARM64_VA_BITS_52
> >> arch/mips/Kconfig:
> >>   depends on SYS_SUPPORTS_HOTPLUG_CPU || !SMP -->
> >>   depends on SYS_SUPPORTS_HOTPLUG_CPU if SMP
> >> arch/riscv/Kconfig:
> >>   depends on CC_HAS_MIN_FUNCTION_ALIGNMENT || !RISCV_ISA_C -->
> >>   depends on CC_HAS_MIN_FUNCTION_ALIGNMENT if RISCV_ISA_C
> >> arch/x86/Kconfig:
> >>   depends on X86_64 || !SPARSEMEM -->
> >>   depends on X86_64 if SPARSEMEM
> >> drivers/acpi/Kconfig:
> >>   depends on ACPI_WMI || !X86 -->
> >>   depends on ACPI_WMI if X86
> >> drivers/bluetooth/Kconfig:
> >>   depends on USB || !BT_HCIBTUSB_MTK
> >>   depends on USB if BT_HCIBTUSB_MTK
> >> mm/Kconfig:
> >>   depends on !ARM || CPU_CACHE_VIPT -->
> >>   depends on CPU_CACHE_VIPT if ARM
> >> kernel/Kconfig.locks:
> >>   depends on !PREEMPTION || ARCH_INLINE_READ_UNLOCK -->
> >>   depends on ARCH_INLINE_READ_UNLOCK if PREEMPTION
> >
> > On the surface, the vast majority these become more readable using the
> > 'if' syntax.
> 
> Agreed, the question is whether a small improvement in
> readability is worth the complexity of having multiple
> ways of expressing the same thing.

It is a tradeoff. Sometimes it is advantageous to increase the 
complexity in one place so other areas with more exposure to more people 
are simplified.


Nicolas