Arm PCIe hotplugging

[Matthew Minter]

Thanks for the help with this. Looking at the design of the board
being worked on it seems that rescan should be enough hopefully (the
pci bus is powered from a separate supply than the SOC so it should be
possible to shut it down during changes.)

However I might also look into the controls provided by PLX to see if
there is anything simple to use to control power per slot.
I shall also look into what the driver support is like fir the PLX
board to see how much work it will be. I am still a novice as far as
PCIe registers go and reading through some specifications so will do
some study and see what I find.

Thank you very much for the advice and help with this. I will
hopefully reply again later if I find or make anything of use for
hotplugging.

On 4 October 2013 17:53, Jason Gunthorpe
<jgunthorpe at obsidianresearch.com> wrote:
> On Fri, Oct 04, 2013 at 02:14:34PM +0100, Matthew Minter wrote:
>
>> I have been doing some work with an Armada XP board (DB-MV784MP-GP)
>> with PCIe support, along with using a PEX 8614 (AA) PCIe switch. The
>> switch in question is said to have hot plug support with the PCIe
>> downstream slots.
>
> PCI-E hot plug has several layers.
>
> The first is the PCI-E serial negotiation and bring up. This is just
> supported out of the box, and works fine with any compliant
> device. You don't need drivers, /sys/bus/pci/rescan is enough. This is
> what I'm doing on kirkwood.
>
> The next is actual *physical* card removal/insertion. For in-box card
> edge connectors this requires power management. You must remove all
> power to the slot before removing/inserting a card. AFAIK, this is
> what the PCI hot plug items in the kernel are all doing, and they do
> this with help from firmware (eg ACPI on x86).
>
> If you have a mechanical system that has staged power connectors (and
> possibly inrush current limiters on the cards) then you don't really
> need to worry much at this point, just rely on the serial hot plug.
>
> PLX (AFIAK) has some 'GPIOs' on their switches dedicated to hot plug
> functions so if the board is properly wired they can control slot
> power/etc through their internal registers. I suspect it shouldn't be
> too hard to get this sort of system to work.. The DT can be augmented
> with slot chassis name properties so you have stable labels work with.
>
> If you have board-specific controls, then you need to start augmenting
> the DT with things like phandles to power regulators and other stuff.
>
>> Looking closer it seems that in the ARM kernel the PCI hotplug code is
>> all disabled. Am I just out of luck and should wait until there is a
>
> I doubt you'll see anything like this emerge in the near future. Fancy
> ARM64 servers with hot plug PCI might motivate the work, but they
> might also do it with ACPI...
>
> BTW,

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