linux-kernel - Re: [RFC PATCH 00/17] Drop uses of pci_read_config

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Message-ID: <6ecce8f3-350a-b5d5-82c9-4609f2298e61@redhat.com>
Date:   Sun, 2 Aug 2020 07:53:46 -0700
From:   Tom Rix <trix@...hat.com>
To:     Borislav Petkov <bp@...en8.de>,
        "Saheed O. Bolarinwa" <refactormyself@...il.com>
Cc:     helgaas@...nel.org, Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Joerg Roedel <joro@...tes.org>, bjorn@...gaas.com,
        skhan@...uxfoundation.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-mtd@...ts.infradead.org, iommu@...ts.linux-foundation.org,
        linux-rdma@...r.kernel.org, linux-ide@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-hwmon@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        linux-gpio@...r.kernel.org, linux-fpga@...r.kernel.org,
        linux-edac@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-crypto@...r.kernel.org,
        linux-atm-general@...ts.sourceforge.net
Subject: Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value


On 8/1/20 5:56 AM, Borislav Petkov wrote:
> On Sat, Aug 01, 2020 at 01:24:29PM +0200, Saheed O. Bolarinwa wrote:
>> The return value of pci_read_config_*() may not indicate a device error.
>> However, the value read by these functions is more likely to indicate
>> this kind of error. This presents two overlapping ways of reporting
>> errors and complicates error checking.
> So why isn't the *value check done in the pci_read_config_* functions
> instead of touching gazillion callers?
>
> For example, pci_conf{1,2}_read() could check whether the u32 *value it
> just read depending on the access method, whether that value is ~0 and
> return proper PCIBIOS_ error in that case.
>
> The check you're replicating
>
> 	if (val32 == (u32)~0)
>
> everywhere, instead, is just ugly and tests a naked value ~0 which
> doesn't mean anything...
>
I agree, if there is a change, it should be in the pci_read_* functions.

Anything returning void should not fail and likely future users of the proposed change will not do the extra checks.

Tom