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

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Message-ID: <1c41b8e1-5b13-463b-c522-6775954c0ee7@amd.com>
Date:   Fri, 30 Jun 2023 12:59:47 -0700
From:   Lizhi Hou <lizhi.hou@....com>
To:     Bjorn Helgaas <helgaas@...nel.org>, Rob Herring <robh@...nel.org>
CC:     <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 6/30/23 09:48, Bjorn Helgaas wrote:
> On Thu, Jun 29, 2023 at 05:52:26PM -0600, Rob Herring wrote:
>> On Thu, Jun 29, 2023 at 05:56:31PM -0500, Bjorn Helgaas wrote:
>>> On Thu, Jun 29, 2023 at 10:19:47AM -0700, Lizhi Hou wrote:
>>>> The PCI endpoint device such as Xilinx Alveo PCI card maps the register
>>>> spaces from multiple hardware peripherals to its PCI BAR. Normally,
>>>> the PCI core discovers devices and BARs using the PCI enumeration process.
>>>> There is no infrastructure to discover the hardware peripherals that are
>>>> present in a PCI device, and which can be accessed through the PCI BARs.
>>> IIUC this is basically a multi-function device except that instead of
>>> each device being a separate PCI Function, they all appear in a single
>>> Function.  That would mean all the devices share the same config space
>>> so a single PCI Command register controls all of them, they all share
>>> the same IRQs (either INTx or MSI/MSI-X), any MMIO registers are likely
>>> in a shared BAR, etc., right?
>> Could be multiple BARs, but yes.
> Where does the PCI glue live?  E.g., who ioremaps the BARs?  Who sets
> up PCI interrupts?  Who enables bus mastering?  The platform driver
> that claims the DT node wouldn't know that this is part of a PCI
> device, so I guess the PCI driver must do all that stuff?  I don't see
> it in the xmgmt-drv.c from
> https://lore.kernel.org/all/20220305052304.726050-4-lizhi.hou@xilinx.com/
>
Yes, the PCI driver will do all that stuff. This xmgmt-drv.c is created

to just populating the devices based on fdt input.  It is removed after

the unittest is created which can populate devices and verify the

address translation.


Thanks,

Lizhi