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

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Message-ID: <CA+55aFxQqxPUP1ppvsR4XOg9x7P-uTUXt6gjHd0actsJKdY1-w@mail.gmail.com>
Date:	Mon, 23 May 2016 11:03:14 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	William Breathitt Gray <vilhelm.gray@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	linux-next <linux-next@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	linux-iio@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Watchdog Mailing List <linux-watchdog@...r.kernel.org>
Subject: Re: [PATCH 1/4] isa: Allow ISA-style drivers on modern systems

On Mon, May 23, 2016 at 7:58 AM, William Breathitt Gray
<vilhelm.gray@...il.com> wrote:
>
> For now, the ISA_BUS Kconfig option is only be available on X86
> architectures. Support for other architectures may be added as required.

So I'd prefer to see that

> +config ISA_BUS_API
> +       def_bool ISA

part in arch/Kconfig.

Why?

Because other architectures _already_ define that ISA symbol, and we
want the "ISA_BUS_API" to be a complete superset of ISA.

So whenever ISA is enabled, ISA_BUS_API should be enabled.

And the way you did that, that's not true. Now, if you were to enable
ISA on ARM, you'd not get ISA_BUS_API. And that sounds insane to me.
It also sounds *wrong* because it effectively changes the meaning of
this:

  --- a/drivers/base/Makefile
  +++ b/drivers/base/Makefile
  @@ -10,7 +10,7 @@ obj-$(CONFIG_DMA_CMA) += dma-contiguous.o
  -obj-$(CONFIG_ISA)      += isa.o
  +obj-$(CONFIG_ISA_BUS_API)      += isa.o

where now that "isa.c" file gets built only on x86, whereas it *used*
to get built whenever ISA was enabled.

So the reason I suggested a separate ISA_BUS_API config option (that
then a particular architecture can choose to enable, in this case the
x86 choice of selecting ISA_BUS) was _exactly_ this issue. The plain
"ISA" config variable is not limited to x86, and the new subset of it
(the ISA_BUS_API) thus also must not be limited to just x86.

               Linus