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Date:   Sun, 2 Aug 2020 22:18:06 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     Saheed Bolarinwa <refactormyself@gmail.com>, trix@redhat.com,
        Kalle Valo <kvalo@codeaurora.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Wolfgang Grandegger <wg@grandegger.com>,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Joerg Roedel <joro@8bytes.org>, bjorn@helgaas.com,
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Subject: Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value
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References: <20200802184648.GA23190@nazgul.tnic>
 <20200802191406.GA248232@bjorn-Precision-5520>
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On Sun, Aug 02, 2020 at 02:14:06PM -0500, Bjorn Helgaas wrote:
> Wait, I'm not convinced yet.  I know that if a PCI read fails, you
> normally get ~0 data because the host bridge fabricates it to complete
> the CPU load.
> 
> But what guarantees that a PCI config register cannot contain ~0?

Well, I don't think you can differentiate that case, right?

I guess this is where the driver knowledge comes into play: if the read
returns ~0, the pci_read_config* should probably return in that case
something like:

	PCIBIOS_READ_MAYBE_FAILED

to denote it is all 1s and then the caller should be able to determine,
based on any of domain:bus:slot.func and whatever else the driver knows
about its hardware, whether the 1s are a valid value or an error.
Hopefully.

Or something better of which I cannot think of right now...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette