Date: Wed, 10 Jun 2009 08:22:15 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-arch@freebsd.org Subject: Re: devclass_find_free_unit Message-ID: <200906100822.15516.jhb@freebsd.org> In-Reply-To: <20090609.174249.-1435625969.imp@bsdimp.com> References: <20090609.174249.-1435625969.imp@bsdimp.com>
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On Tuesday 09 June 2009 7:42:49 pm M. Warner Losh wrote:
> What purpose does devclass_find_free_unit serve? I think it can safely be
> eliminated from the tree. The current design is racy.
>
> Comments?
>
> It is currently used:
>
> ./arm/xscale/ixp425/.svn/text-base/avila_ata.c.svn-base:
device_add_child(dev, "ata", devclass_find_free_unit(ata_devclass, 0));
> ./arm/xscale/ixp425/avila_ata.c: device_add_child(dev, "ata",
devclass_find_free_unit(ata_devclass, 0));
> ./arm/at91/.svn/text-base/at91_cfata.c.svn-base:
device_add_child(dev, "ata", devclass_find_free_unit(ata_devclass, 0));
> ./arm/at91/at91_cfata.c: device_add_child(dev, "ata",
devclass_find_free_unit(ata_devclass, 0));
> ./powerpc/psim/.svn/text-base/ata_iobus.c.svn-base:
devclass_find_free_unit(ata_devclass, 0));
>
> # All the above can be replaced with a simple '-1'.
>
> ata/ata-pci.c: unit : devclass_find_free_unit(ata_devclass, 2));
> ata/ata-usb.c: devclass_find_free_unit(ata_devclass, 2))) ==
NULL) {
>
> These can likely be replaced by '2', but that may result in a warning
> message being printed that likely can be eliminated...
ata does this so it can reserve ata0 and ata1 for the "legacy" ATA channels on
legacy ATA PCI adapters. That is, if you have both SATA controllers and a
PATA controller, this allows the two PATA channels to always be ata0 and ata1
and the PATA drivers to always be ad0 - ad3. You could perhaps implement
this in 8.x now by a really horrendous hack of having ISA hints for ata0 and
ata1 and letting bus_hint_device_unit() in the atapci driver claim those
hints for the channels on PATA controllers.
--
John Baldwin
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