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

From: Andy Shevchenko
Date: Fri Jun 01 2018 - 06:41:35 EST

On Fri, Jun 1, 2018 at 2:50 AM, Logan Gunthorpe <logang@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
> Reviewed-by: Stephen Bates <sbates@xxxxxxxxxxxx>
> Acked-by: Christian KÃnig <christian.koenig@xxxxxxx>

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