Subject: Re: [PATCH 04/10] iio: stx104: Change STX104 dependency to ISA_BUS
To: William Breathitt Gray <vilhelm.gray@gmail.com>
References: <cover.1460040201.git.vilhelm.gray@gmail.com>
 <783be62acf68b35f3fe4785a2cedfe017624688b.1460040201.git.vilhelm.gray@gmail.com>
 <20160408004503.GB10211@roeck-us.net> <20160408123158.GB18202@sophia>
Cc: gregkh@linuxfoundation.org, tglx@linutronix.de, jic23@kernel.org,
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        linus.walleij@linaro.org, gnurou@gmail.com,
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From: Guenter Roeck <linux@roeck-us.net>
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Date: Fri, 8 Apr 2016 06:18:09 -0700
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On 04/08/2016 05:31 AM, William Breathitt Gray wrote:
> On Thu, Apr 07, 2016 at 05:45:03PM -0700, Guenter Roeck wrote:
>> This means for this and other similar drivers that the driver is no longer
>> supported on architectures which support ISA but not the newly introduced
>> ISA_BUS. Affected architectures are alpha, arm, m32r, m68k, mips, powerpc,
>> and parisc.
>>
>> A typical example is SCSI_AHA1542, which is no longer supported on those
>> architectures. It builds, but isa_register_driver() will be a dummy and fail.
>> Actually, this is true for _all_ drivers calling isa_register_driver().
>>
>> I hope this is understood and doesn't cause any problems.
>>
>> Thanks,
>> Guenter
>
> That's a good catch. I overlooked this when I submitted the ISA_BUS
> patch; I had improperly assumed the ISA option to have a dependency on
> X86_32 based on arch/x86/Kconfig. The intention of the ISA_BUS is to
> allow the proper definition of the isa_register_driver and
> isa_unregister_driver functions without the dependency on X86_32 (e.g.
> on X86_64 systems). How can this be resolved without ending support for
> ISA on these other architectures? Would it be appropriate to add the
> ISA_BUS dependency to every "config ISA" block for the other
> architectures?
>
 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.

> 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