linux-kernel - Re: [PATCH 2/3] PCI: of: create DT nodes for PCI devices if they do not exists

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Date:   Wed, 18 May 2022 12:22:07 -0700
From:   Lizhi Hou <lizhi.hou@...inx.com>
To:     Clément Léger <clement.leger@...tlin.com>,
        Bjorn Helgaas <helgaas@...nel.org>
CC:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Allan Nielsen <allan.nielsen@...rochip.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Steen Hegelund <steen.hegelund@...rochip.com>,
        Thomas Petazzoni <thomas.petazonni@...tlin.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Mark Brown <broonie@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Andrew Lunn <andrew@...n.ch>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH 2/3] PCI: of: create DT nodes for PCI devices if they do
 not exists


On 5/4/22 06:43, Clément Léger wrote:
> Le Tue, 3 May 2022 17:53:53 -0500,
> Bjorn Helgaas <helgaas@...nel.org> a écrit :
>
>> In subject:
>>
>>    PCI: of: Create DT nodes ... if they do not exist
>>
>> The subject could be read as saying that you're going to create DT
>> nodes before the PCI devices exist, but I think you mean that when we
>> enumerate a PCI devices, we're *always* going to create a DT node for
>> it, even if the DT didn't mention it.
> Hi Bjorn,
>
> Indeed ! I'll modify that.

Linking the dynamic generated dt node to PCIe device through 
pci_dev->dev.of_node may cause issues. Kernel and driver code may check 
of_node pointer and run complete different code path if of_node is not 
NULL.

For example:  in of_irq_parse_pci(): 
https://elixir.bootlin.com/linux/v5.18-rc2/source/drivers/pci/of.c#L492

I encountered different issues when I tried to create a prototype. And I 
have sent all may questions/thoughts through 
https://lore.kernel.org/lkml/79e4c876-e5a4-861f-cfbc-c75ed1a07ddd@xilinx.com/#t

I am wondering what would be the right way to resolve it?


Thanks,

Lizhi

>
>> Maybe something like:
>>
>>    PCI: of: Create DT node for every PCI device
>>
>> although I see Rob thinks this should be done on demand instead of
>> doing it for every device, which sounds sensible to me.
> Agreed, I'll rework this series.
>
> Thanks,
>
>> On Wed, Apr 27, 2022 at 11:45:01AM +0200, Clément Léger wrote:
>>> In order to apply overlays to PCI device nodes, the nodes must first
>>> exist. This commit add support to populate a skeleton tree for PCI bus
>>> and devices. These nodes can then be used by drivers to apply overlays.
>> s/This commit add support/Add support/
>>
>> Bjorn
>
>