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Subject: Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value
To:     Borislav Petkov <bp@alien8.de>, trix@redhat.com
Cc:     helgaas@kernel.org, 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,
        skhan@linuxfoundation.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
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        linux-i2c@vger.kernel.org, linux-hwmon@vger.kernel.org,
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        linux-edac@vger.kernel.org, dmaengine@vger.kernel.org,
        linux-crypto@vger.kernel.org,
        linux-atm-general@lists.sourceforge.net
References: <20200801112446.149549-1-refactormyself@gmail.com>
 <20200801125657.GA25391@nazgul.tnic>
From:   Saheed Bolarinwa <refactormyself@gmail.com>
Message-ID: <b720aa44-895a-203b-e220-ecdb3acd9278@gmail.com>
Date:   Sun, 2 Aug 2020 19:28:00 +0200
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On 8/1/20 2:56 PM, 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?
Because the value ~0 has a meaning to some drivers and only
drivers have this knowledge. For those cases more checks will
be needed to ensure that it is an error that has actually
happened.
> 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 primary goal is to make pci_config_read*() return void, so
that there is *only* one way to check for error i.e. through the
obtained value.
Again, only the drivers can determine if ~0 is a valid value. This
information is not available inside pci_config_read*().

- Saheed