Hello!
> While diagnosing this problem, I spotted a couple of bits of code that
> worry me in arch/i386/kernel/pci-i386.c. In pcibios_update_resource,
> line 104 we have
>
> new = res->start | (res->flags & PCI_REGION_FLAG_MASK);
>
> When the region type is I/O, that sets the LSB on the new register
> value, e.g. an I/O address of 0x1400 is written to register 0x10 as
> 0x1401. Is that correct?
Yes.
Actually, this should not matter since the region flag bits are
defined as read-only in PCI specs, but it turns out that it really
matters as there exist devices which implement them read-write
and initialize the right values in firmware (!).
> pcibios_enable_resources loops from idx = 0 to idx < 6 to work out
> which flags to set for PCI_COMMAND. In the unlikely event of a card
> which has I/O, no memory but has expansion ROM then PCI_COMMAND will
> only be set to PCI_COMMAND_IO, PCI_COMMAND_MEMORY will not be set.
> Should enable resources check idx <= 6 instead of id < 6, just in case?
You're right, it should check the ROM resource as well, but not the same
way since it's perfectly normal that the ROM resource is unassigned.
This patch should fix it.
--- arch/i386/kernel/pci-i386.c.mj Thu Mar 16 13:26:27 2000
+++ arch/i386/kernel/pci-i386.c Sun Mar 26 00:05:43 2000
@@ -317,5 +317,7 @@
if (r->flags & IORESOURCE_MEM)
cmd |= PCI_COMMAND_MEMORY;
}
+ if (dev->resource[PCI_ROM_RESOURCE].start)
+ cmd |= PCI_COMMAND_MEMORY;
if (cmd != old_cmd) {
printk("PCI: Enabling device %s (%04x -> %04x)\n", dev->slot_name, old_cmd, cmd);
About expansion ROM's themselves:
I don't believe it can make a difference -- unless you're writing your
own program which really runs the firmware in the ROM, there is nobody who
could use the contents of the ROM. Also, you can easily check it by
specifiying "pci=rom" on the kernel command line which makes the kernel
assign address space to all the ROM's.
Also, it is NOT possible to enable the ROM's by default. The PCI specs
allow the ROM address decoder to be shared with one of the decoders for
the I/O or memory regions, so that when the ROM is enabled, you have
no guarantee the other regions will be accessible. One can say this is
just a stupidity of the specs, but believe me, there really exist such
devices.
Have a nice fortnight
-- Martin `MJ' Mares <mj@ucw.cz> <mj@suse.cz> http://atrey.karlin.mff.cuni.cz/~mj/ "Everything counts in large amounts." -- Depeche Mode- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Fri Mar 31 2000 - 21:00:16 EST