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Date:   Sun, 2 Aug 2020 22:18:06 +0200
From:   Borislav Petkov <>
To:     Bjorn Helgaas <>
Cc:     Saheed Bolarinwa <>,,
        Kalle Valo <>,
        "David S. Miller" <>,
        Jakub Kicinski <>,
        Wolfgang Grandegger <>,
        Marc Kleine-Budde <>,
        Miquel Raynal <>,
        Richard Weinberger <>,
        Vignesh Raghavendra <>,
        Joerg Roedel <>,,,,,,,,,,,,,,,,,,,,,
Subject: Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value

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:


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.

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


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