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

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Message-ID: <fb40545a8de8df8914df40d7d6167752c5244ce6.camel@kernel.crashing.org>
Date:   Wed, 15 Jul 2020 12:12:29 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Bjorn Helgaas <helgaas@...nel.org>, Arnd Bergmann <arnd@...db.de>
Cc:     "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 13:45 -0500, Bjorn Helgaas wrote:
> 
> > fail for valid arguments on a valid pci_device* ?
> 
> I really like this idea.
> 
> pci_write_config_*() has one return value, and only 100ish of 2500
> callers check for errors.  It's sometimes possible for config
> accessors to detect PCI errors and return failure, e.g., device was
> removed or didn't respond, but most of them don't, and detecting
> these
> errors is not really that valuable.
> 
> pci_read_config_*() is much more interesting because it returns two
> things, the function return value and the value read from the PCI
> device, and it's complicated to check both. 

  .../...

I agree. It's a mess at the moment.

We have separate mechanism to convey PCI errors (among other things the
channel state) which should apply to config space when detection is
possible.

I think returning all 1's is the right thing to do here and avoids odd
duplicate error detection logic which I bet you is never properly
tested.

> > 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.

Agreed on both points.

Cheers,
Ben.