linux-kernel - Re: [PATCH 04/10] iio: stx104: Change STX104 dependency to ISA

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Date:	Fri, 8 Apr 2016 11:28:01 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	William Breathitt Gray <vilhelm.gray@...il.com>
Cc:	gregkh@...uxfoundation.org, tglx@...utronix.de, jic23@...nel.org,
	knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net, wim@...ana.be,
	linus.walleij@...aro.org, gnurou@...il.com,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	linux-watchdog@...r.kernel.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH 04/10] iio: stx104: Change STX104 dependency to ISA_BUS

On Fri, Apr 08, 2016 at 11:09:22AM -0400, William Breathitt Gray wrote:
> On Fri, Apr 08, 2016 at 06:18:09AM -0700, Guenter Roeck wrote:
> > From the context, arm and mips use "select ISA". For those, adding and
> >auto-selecting ISA_BUS would make sense. For the remaining architectures
> >you could simply add "config ISA_BUS". I would suggest to update default
> >configurations, though.
> >
> >There is also "um", for which you effectively disabled ISA support
> >as far as I can see. You might want to look into that as well.
> >
> >> My avoidance of making ISA a selection of ISA_BUS is the possibility of
> >> an invalid configuration: a user may initially enable ISA_BUS, then
> >> later disable ISA, resulting in ISA_BUS remaining enabled without ISA
> >> selected.
> >>
> >Does that even make sense ? Not sure I understand why you don't just
> >select ISA_BUS if ISA is selected. That would also be backward compatible
> >and avoid the problem I was concerned about.
> 
> I feel now that the introduction of the ISA_BUS option may the wrong
> approach to resolve lack of ISA support for the X86_64 architecture;
> adding ISA_BUS depends or selects through various Kconfigs would simply
> obfuscate the ISA option. The true issue is that various driver
> configs are assuming X86_32 architecture when they depend on the ISA
> option, but the ISA bus does not require an X86_32 architecture.
> 
> The proper resolution then is to remove the misguided ISA_BUS option and
> move the X86_32 dependency to the relevant drivers configs explicitly.
> A grep for isa_register_driver calls within the kernel reveals that only
> a few drivers explicitly use it. It should be trivial to create a patch
> to add the explicit X86_32 dependency to the relevant drivers, so I will
> submit one soon when I get the time to decouple X86_32 from the ISA
> config option.
> 

That might be tricky: At least some if not many of those drivers are expected
to run on non-X86 architectures, and thus don't really depend on X86_32
(possibly some depend on 32 bit - I didn't check).

I count 44 calls to isa_register_driver() in the current mainline.
Not sure if this counts as "only a few drivers".

Thanks,
Guenter

> Once ISA is freed from the X86_32 dependency, I will simply use it
> instead of ISA_BUS, and rebase this patchset for version 2.
> 
> >> As a side note, should the dummy isa_register_driver return 0? Would it
> >> be more appropriate for it to return an error code to indicate lack of
> >> support for ISA, rather than silently fail?
> >>
> >One should think so.
> >
> >Thanks,
> >Guenter
> >
> 
> I'll submit a separate patch for this as well then.
> 
> William Breathitt Gray
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