From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yw0-f195.google.com ([209.85.161.195]:35778 "EHLO mail-yw0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750999AbcFDLM3 (ORCPT ); Sat, 4 Jun 2016 07:12:29 -0400 Date: Sat, 4 Jun 2016 07:12:21 -0400 From: William Breathitt Gray To: Pavel Machek Cc: gregkh@linuxfoundation.org, akpm@linux-foundation.org, x86@kernel.org, linux-next@vger.kernel.org, linux-gpio@vger.kernel.org, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, linux-watchdog@vger.kernel.org, Guenter Roeck , Linus Walleij Subject: Re: [PATCH v2 2/4] gpio: Allow PC/104 devices on X86_64 Message-ID: <20160604111204.GA19180@sophia> References: <20160603205703.GC11253@amd> <20160603211244.GA6831@sophia> <20160604071408.GA22045@amd> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: <20160604071408.GA22045@amd> Sender: linux-iio-owner@vger.kernel.org List-Id: linux-iio@vger.kernel.org On Sat, Jun 04, 2016 at 09:14:08AM +0200, Pavel Machek wrote: >On Fri 2016-06-03 17:12:44, William Breathitt Gray wrote: >> On Fri, Jun 03, 2016 at 10:57:03PM +0200, Pavel Machek wrote: >> >Should we do "depends on PC104" here, because that is what it really >> >means, and have PC104 enabled when ISA_BUS_API is enabled or something >> >like that? >> >> Since the functionality remains the same, I'm a bit indifferent to that >> change; as long as the driver builds for systems in which it's intended >> to be used, I'm satisfied. >> >> Differentiating between PC/104 and ISA may be a pointless endeavor >> though since both buses appear the same to software. But if it is better >> to differentiate between devices as such, then I see little harm in >> adding a PC104 Kconfig option which follows the ISA_BUS_API Kconfig >> option. > >Well, they are same to the software, but not at the hardware. If I >have a development board that has PC104 (but not isa), I'd like to see >prompts for PC104 extensions, not for isa. If PC105 comes out, still >ISA compatible, I will want to see prompts for PC104 boards or PC105 >boards, but not neccessarily both... I think I see the merit of a prompt for PC104 devices. I've encountered a use case recently which I'm curious about in this scenario. Given the compatibility with ISA, manufacturers may occasionally develop variants of existing ISA devices by duplicating the firmware on a PC/104 form factor. I'm working on an IIO DAC driver for the Measurement Computing CIO-DAC family (CIO-DAC08, CIO-DAC16, and PC104-DAC06); while not a GPIO driver, I believe it can serve as a decent example. Interestingly, while the CIO-DAC08 and CIO-DAC16 are true ISA devices, the PC104-DAC06 is a PC/104 variant compatible with the others in the family. The IIO DAC driver works just as well with the PC104-DAC06, as it does with the true ISA devices in the family. What would the Kconfig depends line look in this scenario? I imagine simply "depends on PC104" would be inappropriate since there are a number of true ISA devices supported by the driver, but "depends on ISA_BUS_API || PC104" seems somewhat redundant when the PC104 Kconfig option implies ISA_BUS_API. This situation isn't that much of an issue overall, but I anticipate encountering it occassionally as I develop future PC/104 drivers. William Breathitt Gray