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Subject: Re: [RFC PATCH 00/35] Move all PCIBIOS* definitions into arch/x86
From:   Benjamin Herrenschmidt <benh@kernel.crashing.org>
To:     Bjorn Helgaas <helgaas@kernel.org>, Arnd Bergmann <arnd@arndb.de>
Cc:     "Saheed O. Bolarinwa" <refactormyself@gmail.com>,
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        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Michael Ellerman <mpe@ellerman.id.au>,
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        Sagi Grimberg <sagi@grimberg.me>,
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        Rob Herring <robh@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Kevin Hilman <khilman@baylibre.com>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Jingoo Han <jingoohan1@gmail.com>,
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Date:   Wed, 15 Jul 2020 12:12:29 +1000
In-Reply-To: <20200714184550.GA397277@bjorn-Precision-5520>
References: <20200714184550.GA397277@bjorn-Precision-5520>
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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.