linux-kernel - Re: [PATCH V10 2/5] PCI: Create device tree node for bridge

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Message-ID: <CAL_JsqLzGted2tYHM7uKZRYDHypz4P6KMXGDuYLgpYsJcUyU8Q@mail.gmail.com>
Date:   Tue, 18 Jul 2023 12:15:18 -0600
From:   Rob Herring <robh@...nel.org>
To:     Lizhi Hou <lizhi.hou@....com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>, linux-pci@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        max.zhen@....com, sonal.santan@....com,
        stefano.stabellini@...inx.com
Subject: Re: [PATCH V10 2/5] PCI: Create device tree node for bridge

On Fri, Jun 30, 2023 at 12:25 PM Lizhi Hou <lizhi.hou@....com> wrote:
>
>
> On 6/29/23 16:52, Rob Herring wrote:
> >>> +                   rp[i].child_addr[0] = j;
> >>> +   ret = of_changeset_add_empty_prop(ocs, np, "dynamic");
> >> It seems slightly confusing to use a "dynamic" property here when we
> >> also have the OF_DYNAMIC dynamic flag above.  I think they have
> >> different meanings, don't they?
> > Hum, what's the property for? It's new in this version. Any DT property
> > needs to be documented, but I don't see why we need it.
>
> This is mentioned in my previous reply for V9
>
> https://lore.kernel.org/lkml/af9b6bb3-a98d-4fb6-b51e-b48bca61dada@amd.com/
>
> As we discussed before, "interrupt-map" was intended to be used here.
>
> And after thinking it more, it may not work for the cases where ppnode
>
> is not dynamically generated and it does not have "interrupt-map".
>
> For example the IBM ppc system, its device tree has nodes for pci bridge
>
> and it does not have "interrupt-map".

How do you know? I ask because usually the only way I have visibility
there is when I break something. In traditional OpenFirmware, which
IBM PPC is, all PCI devices have a DT node because it's the firmware
telling the OS "these are the devices I discovered and this is how I
configured them".

> Based on previous discussions, OF_DYNAMIC should not be used here.

For the same reasons, I don't think the behavior should change based
on being dynamic. Now maybe the behavior when it's an ACPI system with
DT overlays has to change, but that's a problem for later. I don't yet
know if we'd handle that here somehow or elsewhere so that this node
looks like a normal DT system.

This should all work the same whether we've generated the nodes or
they were already present in the FDT when we booted.

> So I think adding "dynamic" might be a way to identify the dynamically
>
> added node. Or we can introduce a new flag e.g OF_IRQ_SWIZZLING.

I hope not. The flags tend to be hacks.

Rob