Date: Mon, 02 Oct 2006 11:39:54 -0600 (MDT) From: "M. Warner Losh" <imp@bsdimp.com> To: john@baldwin.cx Cc: freebsd-new-bus@freebsd.org Subject: Re: Properly managing sub-allocations Message-ID: <20061002.113954.756907493.imp@bsdimp.com> In-Reply-To: <200610021323.50997.john@baldwin.cx> References: <200610021323.50997.john@baldwin.cx>
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In message: <200610021323.50997.john@baldwin.cx>
John Baldwin <john@baldwin.cx> writes:
: I'm trying to cleanup a few things in apci and I ran into what I think is a
: new-bus architecture issue. Specifically, acpi likes to allocate system
: resource resources from its parent, and then turn around and sub-alloc those
: out to children. This mostly works fine except for the bus space details of
: the bus tag and bus handle. Currently acpi(4) just copies the tag from the
: corresponding resource from the parent and sets the handle to the start of
: the resource. This just happens to work currently because i386 and amd64 use
: the start of the resource for the handle for SYS_RES_IO and overwrite the
: handle in nexus_activate_resource() for SYS_RES_MEMORY. This does add some
: ugliness though in that acpi needs to go find the parent resouce to copy the
: bus tag. However, it's current algorithm wouldn't work in general (PC98
: needs to alloc bus handles, and it does so in nexus_alloc_resource() for
: example).
:
: To solve this, I think we need to stop setting bus tags and handles in
: bus_alloc_resource(). One solution might be to add a new bus method to set
: those for a resource, but I think the better solution would be to set the bus
: tags and handles in bus_activate_resource(). It already sort of does this
: for some cases (SYS_RES_MEMORY on x86 for example) and will work with the
: existing ACPI model (it already passes up activate_resource to the parent, so
: we would just have to remove the explicit setting of the bus tag and handle).
:
: I actually wonder if this isn't how things are supposed to be in the first
: place and that the current aberrations are just bugs?
I think you are right. Thinking about it, you can't access the
resources until you've activated them...
However, this may break some existing drivers that allocate a BAR,
peek at its type and then either activate it or allocate another
BAR... The TAG is valid, but the handle isn't.
This specific problem will never happen in pc98, since there are no
ACPI pc98 machines and can never be.
Warner
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