linux-kernel - Re: [PATCH v3 1/3] PCI: Make specifying PCI devices in kernel parameters reusable

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Message-ID: <c2053508-0880-5b7b-fd2f-260d260f33f9@deltatee.com>
Date:   Mon, 18 Jun 2018 15:49:49 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-doc@...r.kernel.org, Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH v3 1/3] PCI: Make specifying PCI devices in kernel
 parameters reusable

On 6/18/2018 3:44 PM, Alex Williamson wrote:
>> + *
>> + * The second format matches devices using IDs in the configuration
>> + * space which may match multiple devices in the system. A value of 0
>> + * for any field will match all devices.
> 
> I realize this is not a change in behavior, but since we're spelling it
> out in a proper comment rather than burying it in the implementation,
> using 0 as a wildcard is rather questionable behavior.  It always
> surprises me when I read this because pci_match_one_device() uses
> PCI_ANY_ID (~0) as a wildcard and as a result of struct pci_device_id
> using __u32 for these fields, we actually need to specify ffffffff on
> the commandline to get a wildcard match for dynamic ids.  The latter is
> tedious to use, but I think it's more correct, and the use of a __u32 is
> probably attributed to the fact that 0xffff is only reserved for vendor
> ID, the spec doesn't seem to reserve any entries from the vendor's
> device ID range.
> 
> There's probably really no path to resolve these, but acknowledging the
> difference in this comment block might be helpful in the future.

Ok, I'll add a note in the comment.
>> +		ret = pci_dev_str_match(dev, p, &p);
>> +		if (ret == 1) {
>> +			*resize = true;
>> +			if (align_order == -1)
>> +				align = PAGE_SIZE;
>> +			else
>> +				align = 1 << align_order;
>> +			break;
>> +		} else if (ret < 0) {
>> +			pr_info("PCI: Can't parse resource_alignment parameter: pci:%s\n",
> 
> 
> The "pci:" prefix on %s doesn't make sense now, it was used above when
> the pointer was already advanced past this token, now I believe it would
> lead to "pci:pci:xxxx:yyyy" or "pci:xx:yy.z".  Thanks,

Yup, nice catch. I'll fix it for v4.

Logan