linux-kernel - Re: [PATCH 10/10] x86/Kconfig: remove CONFIG_ISA

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Date:   Mon, 28 Feb 2022 18:26:08 -0500
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Mateusz Jończyk <mat.jonczyk@...pl>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 10/10] x86/Kconfig: remove CONFIG_ISA_BUS

On Mon, Feb 28, 2022 at 10:28:26PM +0100, Mateusz Jończyk wrote:
> CONFIG_ISA_BUS was used only as a dependency for a single Industrial IO
> driver: CONFIG_CIO_DAC ("Measurement Computing CIO-DAC IIO driver"). At
> least grepping the kernel source for "ISA_BUS" did not find any other
> meaningful results.
> 
> There are more configuration options that select CONFIG_ISA_BUS_API, but
> did not depend on CONFIG_ISA_BUS. Most of these are for Industrial IO and
> GPIO drivers.
> 
> Signed-off-by: Mateusz Jończyk <mat.jonczyk@...pl>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: x86@...nel.org
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: William Breathitt Gray <vilhelm.gray@...il.com>

For context, the Measurement Computing CIO-DAC device comes in two
form factors: PC104 and ISA. The PC104 bus is typically aimed at
embedded systems and not commonly used by general users, so the
CONFIG_PC104 Kconfig option was introduced to filter out these devices
for most users who would generally not be interested in them. Because
the CIO-DAC device is also available in an ISA form factor, I needed a
way to have the CONFIG_CIO_DAC Kconfig available even on non-PC104
systems; that's how the CONFIG_ISA_BUS Kconfig option came about.

The purpose of the CONFIG_ISA_BUS Kconfig option is filter out ISA bus
devices because few users will have an ISA bus. I suppose it does no
harm to remove that filter because users can still select CONFIG_CIO_DAC
if they want it, so I'm all right with this patch.

Acked-by: William Breathitt Gray <vilhelm.gray@...il.com>

> ---
>  arch/x86/Kconfig        | 11 -----------
>  drivers/iio/dac/Kconfig |  2 +-
>  2 files changed, 1 insertion(+), 12 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 19acc5954083..2de46adfbde2 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2692,17 +2692,6 @@ config PCI_CNB20LE_QUIRK
>  
>  	  You should say N unless you know you need this.
>  
> -config ISA_BUS
> -	bool "ISA bus support on modern systems" if EXPERT
> -	help
> -	  Expose ISA bus device drivers and options available for selection and
> -	  configuration. Enable this option if your target machine has an ISA
> -	  bus. ISA is an older system, displaced by PCI and newer bus
> -	  architectures -- if your target machine is modern, it probably does
> -	  not have an ISA bus.
> -
> -	  If unsure, say N.
> -
>  # x86_64 have no ISA slots, but can have ISA-style DMA.
>  config ISA_DMA_API
>  	bool "ISA-style DMA support" if (X86_64 && EXPERT)
> diff --git a/drivers/iio/dac/Kconfig b/drivers/iio/dac/Kconfig
> index bfcf7568de32..fe0f2a93055d 100644
> --- a/drivers/iio/dac/Kconfig
> +++ b/drivers/iio/dac/Kconfig
> @@ -264,7 +264,7 @@ config AD8801
>  
>  config CIO_DAC
>  	tristate "Measurement Computing CIO-DAC IIO driver"
> -	depends on X86 && (ISA_BUS || PC104)
> +	depends on X86
>  	select ISA_BUS_API
>  	help
>  	  Say yes here to build support for the Measurement Computing CIO-DAC
> -- 
> 2.25.1
>