Date: Fri, 6 Jul 2012 14:46:40 -0400 From: Arnaud Lacombe <lacombar@gmail.com> To: Warner Losh <imp@bsdimp.com> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org>, FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: Interfacing devices with multiple parents within newbus Message-ID: <CACqU3MX_xoHQ2HbvhUdj%2BVM4Dt34jANnhGkRG_xO6DM69AFc2Q@mail.gmail.com> In-Reply-To: <CACqU3MWTKSpVRbJracCjSLVHko8RSpXw6vpC3o3UaAyTizos3A@mail.gmail.com> References: <CACqU3MU6iv%2Bo26fCdL5M6Kg6XMM1uZPih5FBiBKPOD9WDx%2BNGg@mail.gmail.com> <FEAC4049-11B0-4B3D-BB7A-0946DBBFF530@bsdimp.com> <CACqU3MWTKSpVRbJracCjSLVHko8RSpXw6vpC3o3UaAyTizos3A@mail.gmail.com>
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Hi, On Fri, Jul 6, 2012 at 11:33 AM, Arnaud Lacombe <lacombar@gmail.com> wrote: > That's neither correct nor robust in a couple of way: > 1) you have no guarantee a device unit will always give you the same resource. this raises the following question: how can a device, today, figure out which parent in a given devclass would give it access to resources it needs. Say, you have gpiobus0 provided by a superio and gpiobus1 provided by the chipset and a LED on the chipset's GPIO. Now, say gpiobus0 attachment is conditional to some BIOS setting. How can you tell gpioled(4) to attach on the chipset provided GPIO without hardcoding unit number either way ? AFAIK, you can not. Even hints provided layout description is defeated. Each device in a given devclass need to have a set of unique attribute to allow a child to distinguish it from other potential parent in the same devclass... - Arnaud
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