linux-kernel - Re: [PATCH RFC V3 2/2] PCI: Create device tree node for selected devices

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Date:   Tue, 8 Nov 2022 12:50:43 -0800
From:   Lizhi Hou <lizhi.hou@....com>
To:     Bjorn Helgaas <helgaas@...nel.org>
CC:     <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <robh@...nel.org>,
        <frowand.list@...il.com>, <clement.leger@...tlin.com>,
        <max.zhen@....com>, <sonal.santan@....com>, <larry.liu@....com>,
        <brian.xu@....com>, <stefano.stabellini@...inx.com>,
        <trix@...hat.com>
Subject: Re: [PATCH RFC V3 2/2] PCI: Create device tree node for selected
 devices

Hi Bjorn,

Thanks for your comments. I will fix all these with next submission.

Lizhi

On 11/7/22 13:05, Bjorn Helgaas wrote:
> On Fri, Nov 04, 2022 at 08:24:14AM -0700, Lizhi Hou wrote:
>> The PCIe endpoint device such as Xilinx Alveo PCIe card maps the register
>> spaces from multiple hardware peripherals to its PCIe 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.
>>
>> For Alveo PCIe card, the card firmware provides a flattened device tree to
>> describe the hardware peripherals on its BARs. The Alveo card driver can
>> load this flattened device tree and leverage device tree framework to
>> generate platform devices for the hardware peripherals eventually.
>>
>> Apparently, the device tree framework requires a device tree node for the
>> PCIe device. Thus, it can generate the device tree nodes for hardware
>> peripherals underneath. Because PCIe is self discoverable bus, there might
>> not be a device tree node created for PCIe devices. This patch is to add
>> support to generate device tree node for PCIe devices. It introduces a
>> kernel option. When the option is turned on, the kernel will generate
> Specify the kernel option here.  These last two sentences should
> probably be a separate paragraph because they say specifically what
> this patch does.
>
>> device tree nodes for PCI bridges unconditionally.
>> It will also generate
>> a device tree node for Xilinx Alveo U50 by using PCI quirks.
> I think I would split the Xilinx Alveo U50 quirk to a separate patch
> from the infrastructure and make this patch more generic.
>
>> +config PCI_DYNAMIC_OF_NODES
>> +	bool "Device tree node for PCI devices"
>> +	depends on OF
>> +	select OF_DYNAMIC
>> +	help
>> +	  This option enables support for generating device tree nodes for some
>> +	  PCI devices. Thus, the driver of this kind can load and overlay
>> +	  flattened device tree for its downstream devices.
>> +
>> +	  Once this option is selected, the device tree nodes will be generated
>> +	  for all PCI/PCIE bridges.
> PCI/PCIe
>
> Actually, in this context (and in the commit log), you should just say
> "PCI" because there's nothing PCIe-specific here.
>
>> +void of_pci_make_dev_node(struct pci_dev *pdev)
>> +{
>> +	struct device_node *parent, *dt_node = NULL;
>> +	const char *pci_type = "dev";
>> +	struct of_changeset *cset;
>> +	const char *full_name;
>> +	int ret;
>> +
>> +	/*
>> +	 * if there is already a device tree node linked to this device,
>> +	 * return immediately.
> s/if there/If there/
>
>> +	 */
>> +	if (pci_device_to_OF_node(pdev))
>> +		return;
>> +
>> +	/* check if there is device tree node for parent device */
> s/check/Check/
>
> Follow the style of the file, which is "capitalize English sentences."