From: Benjamin Herrenschmidt <benh@kernel•crashing.org>
To: Bjorn Helgaas <bhelgaas@google•com>
Cc: linux-arch@vger•kernel.org, Tony Luck <tony.luck@intel•com>,
Yinghai Lu <yinghai@kernel•org>,
linuxppc-dev@lists•ozlabs.org, linux-pci@vger•kernel.org,
linux-kernel@vger•kernel.org,
Dominik Brodowski <linux@dominikbrodowski•net>,
Paul Mackerras <paulus@samba•org>,
Jesse Barnes <jbarnes@virtuousgeek•org>,
Greg Kroah-Hartman <gregkh@linuxfoundation•org>,
Andrew Morton <akpm@linux-foundation•org>,
Linus Torvalds <torvalds@linux-foundation•org>
Subject: Re: [PATCH 08/18] PCI, powerpc: Register busn_res for root buses
Date: Tue, 28 Feb 2012 19:54:32 +1100 [thread overview]
Message-ID: <1330419272.11728.27.camel@pasglop> (raw)
In-Reply-To: <CAErSpo4bw-V=SM+h5iP4nfv3HaAnHjwvNwu+4Oz8iyQcY_3gOQ@mail.gmail.com>
On Mon, 2012-02-27 at 22:36 -0700, Bjorn Helgaas wrote:
>
> There's a lot of powerpc code that does this:
>
> bus_range = of_get_property(pcictrl, "bus-range", &len);
> hose->first_busno = bus_range[0];
> hose->last_busno = bus_range[1];
>
> That *looks* like it is discovering the bus number aperture. Is it?
> If it is, why are we using the largest bus number found by
> pci_scan_child_bus() rather than "last_busno"?
We do that but we somewhat -also- rely on the core bumping it if it
needs to make room :-)
As I said, we are swimming in dirty waters between reverse engineered
stuff we don't know 100% and "designed" stuff.
I think we should have ways to more explicitely define what we want tho,
ie whether hose->last_busno is just what happens to be the "current" bus
number assigned by the firmware or the hard max. Maybe a pci flag ?
On the other hand some platforms (all the ppc4xx ones for example) set
the flag to reassign all busses ... but have limit on bus numbers simply
because they have a memory mapped only config space and we don't have
enough address space to ioremap it all on 32-bit.
We need to fix them to use a fixmap entry to do atomic on-demand mapping
of the config space and lift that restriction, but that isn't done yet.
So I think those patches will need really careful handling on our side.
Cheers,
Ben.
next prev parent reply other threads:[~2012-02-28 8:54 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1330395009-29260-1-git-send-email-yinghai@kernel.org>
2012-02-28 2:09 ` [PATCH 08/18] PCI, powerpc: Register busn_res for root buses Yinghai Lu
2012-02-28 5:36 ` Bjorn Helgaas
2012-02-28 8:54 ` Benjamin Herrenschmidt [this message]
2012-02-28 23:31 ` Bjorn Helgaas
2012-02-28 23:41 ` Benjamin Herrenschmidt
2012-04-02 9:58 ` Milton Miller
2012-04-02 10:19 ` Milton Miller
2012-04-02 21:22 ` Benjamin Herrenschmidt
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