linux-kernel - Re: [PATCH 1/4] isa: Allow ISA-style drivers on modern systems

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Date:	Mon, 23 May 2016 10:21:25 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	William Breathitt Gray <vilhelm.gray@...il.com>
Cc:	gregkh@...uxfoundation.org, akpm@...ux-foundation.org,
	x86@...nel.org, linux-next@...r.kernel.org,
	linux-gpio@...r.kernel.org, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-watchdog@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/4] isa: Allow ISA-style drivers on modern systems

On Mon, May 23, 2016 at 10:58:41AM -0400, William Breathitt Gray wrote:
> Several modern devices, such as PC/104 cards, are expected to run on
> modern systems via an ISA bus interface. Since ISA is a legacy interface
> for most modern architectures, ISA support should remain disabled in
> general. Support for ISA-style drivers should be enabled on a per driver
> basis.
> 
> To allow ISA-style drivers on modern systems, this patch introduces the
> ISA_BUS_API and ISA_BUS Kconfig options. The X86 ISA bus driver will now
> build conditionally on the ISA_BUS_API Kconfig option, which defaults to
> the legacy ISA Kconfig option. The ISA_BUS Kconfig option allows the
> ISA_BUS_API Kconfig option to be selected on architectures which do not
> enable ISA (e.g. X86_64).
> 
> For now, the ISA_BUS Kconfig option is only be available on X86
> architectures. Support for other architectures may be added as required.
> 
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: William Breathitt Gray <vilhelm.gray@...il.com>
> ---
>  arch/x86/Kconfig      | 13 +++++++++++++
>  drivers/base/Makefile |  2 +-
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 0a7b885..a41c0b8 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2439,6 +2439,19 @@ config PCI_CNB20LE_QUIRK
>  
>  source "drivers/pci/Kconfig"
>  
> +config ISA_BUS_API
> +	def_bool ISA
> +
> +config ISA_BUS
> +	bool "ISA-style bus support on modern systems" if (X86 && EXPERT)
> +	default y

Sure you want it enabled by default ?

> +	select ISA_BUS_API
> +	help
> +	  Enables ISA-style drivers on modern systems. This is necessary to
> +	  support PC/104 devices on X86_64 platforms.
> +
> +	  If unsure, say Y.
> +
>  # 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/base/Makefile b/drivers/base/Makefile
> index 6b2a84e..2609ba2 100644
> --- a/drivers/base/Makefile
> +++ b/drivers/base/Makefile
> @@ -10,7 +10,7 @@ obj-$(CONFIG_DMA_CMA) += dma-contiguous.o
>  obj-y			+= power/
>  obj-$(CONFIG_HAS_DMA)	+= dma-mapping.o
>  obj-$(CONFIG_HAVE_GENERIC_DMA_COHERENT) += dma-coherent.o
> -obj-$(CONFIG_ISA)	+= isa.o
> +obj-$(CONFIG_ISA_BUS_API)	+= isa.o

Unless I am missing something, this is insufficient, and I am a bit surprised
that it actually works. include/linux/isa.h declares isa_register_driver()
and isa_unregister_driver() as dummies if CONFIG_ISA is not enabled.
Doesn't this cause a compile error ? Confused.

Thanks,
Guenter

>  obj-$(CONFIG_FW_LOADER)	+= firmware_class.o
>  obj-$(CONFIG_NUMA)	+= node.o
>  obj-$(CONFIG_MEMORY_HOTPLUG_SPARSE) += memory.o
> -- 
> 2.7.3
> 
> --
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