linux-kernel - Re: lspci: Display path to device

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Message-ID: <mj+md-20180810.091549.51451.nikam@ucw.cz>
Date:   Fri, 10 Aug 2018 11:35:01 +0200
From:   Martin Mares <mj@....cz>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        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>,
        Alex Williamson <alex.williamson@...hat.com>,
        Christian König <christian.koenig@....com>
Subject: Re: lspci: Display path to device

Hello!

> I don't like telling the user to grovel around lspci -t by hand.  It's
> not many lines of code to add a new -P option to lspci to show the path
> to each device instead of bus:dev.fn

I like the feature, but I have a couple of minor objections to the
implementation:

> -static char options[] = "nvbxs:d:ti:mgp:qkMDQ" GENERIC_OPTIONS ;
> +static char options[] = "nvbxs:d:tPi:mgp:qkMDQ" GENERIC_OPTIONS ;

Please update the help_msg, too.

> +static void
> +show_slot_path(struct pci_dev *p)
> +{
> +  struct pci_dev *d = NULL;
> +
> +  if (opt_path && p->bus)
> +    {
> +      for (d = p->access->devices; d; d = d->next) {
> +	if (d->hdrtype == -1)
> +	  d->hdrtype = pci_read_byte(d, PCI_HEADER_TYPE) & 0x7f;

Please do not modify the hdrtype field, it is private to libpci.

Instead, always read the PCI_HEADER_TYPE register. It will be fast since
lspci caches configuration space accesses.

> +	if (d->hdrtype != PCI_HEADER_TYPE_BRIDGE &&
> +	    d->hdrtype != PCI_HEADER_TYPE_CARDBUS)
> +	  continue;
> +	if (pci_read_byte(d, PCI_SECONDARY_BUS) > p->bus)
> +	  continue;
> +	if (pci_read_byte(d, PCI_SUBORDINATE_BUS) < p->bus)
> +	  continue;

Beware, cardbus bridges use different registers for secondary and subordinate bus.

... the more I think about it, the more I am convinced that we want to
re-use the bus topology builder from ls-tree.c. I will give it a try,
stay tuned.

				Martin