linux-kernel - Re: [PATCH v2 2/3] PCI: Allow specifying devices using a base bus and path of devfns

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Message-ID: <CAHp75Vc4yxeM+jz2biMBoWB-h_dG1_Qx91VCP+f1mhvvgPVPxQ@mail.gmail.com>
Date:   Fri, 1 Jun 2018 13:41:20 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org,
        Linux Documentation List <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: [PATCH v2 2/3] PCI: Allow specifying devices using a base bus and
 path of devfns

On Fri, Jun 1, 2018 at 2:50 AM, Logan Gunthorpe <logang@...tatee.com> wrote:
> When specifying PCI devices on the kernel command line using a
> BDF, the bus numbers can change when adding or replacing a device,
> changing motherboard firmware, or applying kernel parameters like
> pci=assign-buses. When this happens, it is usually undesirable to
> apply whatever command line tweak to the wrong device.
>
> Therefore, it is useful to be able to specify devices with a base
> bus number and the path of devfns needed to get to it. (Similar to
> the "device scope" structure in the Intel VT-d spec, Section 8.3.1.)
>
> Thus, we add an option to specify devices in the following format:
>
> path:[<domain>:]<bus>:<slot>.<func>/<slot>.<func>[/ ...]
>
> The path can be any segment within the PCI hierarchy of any length and
> determined through the use of 'lspci -t'. When specified this way, it is
> less likely that a renumbered bus will result in a valid device specification
> and the tweak won't be applied to the wrong device.
>
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> Reviewed-by: Stephen Bates <sbates@...thlin.com>
> Acked-by: Christian König <christian.koenig@....com>

> -                               specified in one of two formats:
> +                               specified in one of three formats:

...in one of the following formats:

in the first place and don't fix it each time you add/remove one?


-- 
With Best Regards,
Andy Shevchenko