Date: Sat, 7 Jul 2012 14:25:36 +0200 From: Stefan Bethke <stb@lassitu.de> To: Arnaud Lacombe <lacombar@gmail.com> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org>, FreeBSD Current <freebsd-current@freebsd.org>, Warner Losh <imp@bsdimp.com> Subject: Re: Interfacing devices with multiple parents within newbus Message-ID: <A1DF0EAD-65A4-4231-9F4B-08D8443BC241@lassitu.de> 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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Am 06.07.2012 um 17:33 schrieb Arnaud Lacombe: > I assume you are talking about = devclass_get_device()/device_find_child(). >=20 > 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. > 2) there is no reference counting on the returned device. > 3) there is no track record of the reference being given. >=20 > About (1), lower unit devices can fails to attach[0], thus newly > attached bus will now have a negative offset. >=20 > About (2) and (3), referenced device (think KLD) might go away and the > child will not be told. In this situation, I want the child to be > detached prior to its parent. >=20 > As such, looking up other node by name would fit in what I call > "bypassing newbus purpose". I might just as well export a damn > function pointer and make my life easier. I believe there is one more thing that needs to be addressed, which I = ran into while trying to do the arge/mdio attachment: 4) the device attach method may require access to the other device to = complete the attachment, but that other might not be attached yet. Circular dependencies nonwithstanding, it would be highly desirable for = a device driver developer to be able to simply declare all prerequisites = for attachment, and have newbus call attach only after everything is = there. Right now, the drivers attach method is called by the parent bus = as soon as enumeration is completed. A notification mechanism (similar to the devfs notification but with an = exposed KPI) might be an alternative, as mentioned in this thread. Stefan --=20 Stefan Bethke <stb@lassitu.de> Fon +49 151 14070811
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