Date: Sun, 16 Jan 2000 16:06:25 +0000 (GMT) From: Doug Rabson <dfr@nlsystems.com> To: Michael Kennett <mike@laurasia.com.au> Cc: hackers@freebsd.org Subject: Re: Use of newbus in sys/pci/pci.c Message-ID: <Pine.BSF.4.10.10001161601110.25118-100000@salmon.nlsystems.com> In-Reply-To: <200001150332.LAA24167@laurasia.com.au>
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On Sat, 15 Jan 2000, Michael Kennett wrote:
> Hello All,
>
> I have a question on the sys/pci/pci.c code, and its use of the
> newbus architecture. An example of the code in question is:
>
> static struct resource *
> pci_alloc_resource(device_t dev, device_t child, int type, int *rid,
> u_long start, u_long end, u_long count, u_int flags)
> {
> struct pci_devinfo *dinfo = device_get_ivars(child);
> ^^^^^ Looks wrong
> struct resource_list *rl = &dinfo->resources;
>
> return resource_list_alloc(rl, dev, child, type, rid,
> start, end, count, flags);
> }
>
> I don't understand the line that extracts the ivars from the child
> device. Isn't it the case that the ivars are a property of the bus
> device (dev)? In any case, the child device might not be directly
> descended from the pci bus (e.g. it could be attached thru' the
> bridge isab0: <VIA 82C586 PCI-ISA bridge>).
The ivars are for bus-specific per-child information. The resource
locations for pci devices fall into this category and the information is
stored in a pci-private structure in the child device's ivars field.
This code is slightly dubious for the case when child isn't a direct
descendant of dev (i.e. a grandchild etc). In this case, the ivars pointer
would be read but not indirected through since the first thing
resource_list_alloc() does is check for this and pass the allocation up
the tree. It should be safe but its certainly dubious.
--
Doug Rabson Mail: dfr@nlsystems.com
Nonlinear Systems Ltd. Phone: +44 181 442 9037
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