linux-kernel - Re: [RFC PATCH 00/35] Move all PCIBIOS* definitions into arch/x86

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Date:   Wed, 15 Jul 2020 12:14:09 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Kjetil Oftedal <oftedal@...il.com>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        "Saheed O. Bolarinwa" <refactormyself@...il.com>,
        bjorn@...gaas.com, Shuah Khan <skhan@...uxfoundation.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Russell King <linux@...linux.org.uk>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        "David S. Miller" <davem@...emloft.net>,
        sparclinux <sparclinux@...r.kernel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kevin Hilman <khilman@...libre.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Toan Le <toan@...amperecomputing.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Ley Foon Tan <ley.foon.tan@...el.com>,
        Marek Vasut <marek.vasut+renesas@...il.com>
Subject: Re: [RFC PATCH 00/35] Move all PCIBIOS* definitions into arch/x86

On Tue, 2020-07-14 at 23:02 +0200, Kjetil Oftedal wrote:
> > 
> > > For b), it might be nice to also change other aspects of the
> > > interface, e.g. passing a pci_host_bridge pointer plus bus number
> > > instead of a pci_bus pointer, or having the callback in the
> > > pci_host_bridge structure.
> > 
> > I like this idea a lot, too.  I think the fact that
> > pci_bus_read_config_word() requires a pci_bus * complicates things in
> > a few places.
> > 
> > I think it's completely separate, as you say, and we should defer it
> > for now because even part a) is a lot of work.  I added it to my list
> > of possible future projects.
> > 
> 
> What about strange PCI devices such as Non-Transparent bridges?
> They will require their own PCI Config space accessors that is not
> connected to a host bridge if one wants to do some sort of
> punch-through enumeration.
> I guess the kernel doesn't care much about them?

Well, today they would require a pci_bus anyway.. . so if you want to do
that sort of funny trick you may as well create a "virtual" host bridge.

Cheers,
Ben.