linux-kernel - Re: [PATCH v5 3/3] PCI: xilinx-cpm: Add support for Versal Net CPM5NC Root Port controller

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Message-ID: <20250310170717.GA556500@bhelgaas>
Date: Mon, 10 Mar 2025 12:07:17 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Thippeswamy Havalige <thippeswamy.havalige@....com>
Cc: bhelgaas@...gle.com, lpieralisi@...nel.org, kw@...ux.com,
	manivannan.sadhasivam@...aro.org, robh@...nel.org,
	krzk+dt@...nel.org, conor+dt@...nel.org, linux-pci@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	michal.simek@....com, bharat.kumar.gogada@....com
Subject: Re: [PATCH v5 3/3] PCI: xilinx-cpm: Add support for Versal Net
 CPM5NC Root Port controller

On Mon, Feb 24, 2025 at 09:20:24PM +0530, Thippeswamy Havalige wrote:
> The Versal Net ACAP (Adaptive Compute Acceleration Platform) devices
> incorporate the Coherency and PCIe Gen5 Module, specifically the
> Next-Generation Compact Module (CPM5NC).
> 
> The integrated CPM5NC block, along with the built-in bridge, can function
> as a PCIe Root Port & supports the PCIe Gen5 protocol with data transfer
> rates of up to 32 GT/s, capable of supporting up to a x16 lane-width
> configuration.
> 
> Bridge errors are managed using a specific interrupt line designed for
> CPM5N. INTx interrupt support is not available.
> 
> Currently in this commit platform specific Bridge errors support is not
> added.

> @@ -478,6 +479,9 @@ static void xilinx_cpm_pcie_init_port(struct xilinx_cpm_pcie *port)
>  {
>  	const struct xilinx_cpm_variant *variant = port->variant;
>  
> +	if (variant->version != CPM5NC_HOST)
> +		return;

You're adding support for CPM5NC_HOST, but this changes the behavior
for all the NON-CPM5NC_HOST devices, which looks like a typo.

Should it be "variant->version == CPM5NC_HOST" instead?

>  	if (cpm_pcie_link_up(port))
>  		dev_info(port->dev, "PCIe Link is UP\n");
>  	else
> @@ -578,9 +582,13 @@ static int xilinx_cpm_pcie_probe(struct platform_device *pdev)
>  
>  	port->dev = dev;
>  
> -	err = xilinx_cpm_pcie_init_irq_domain(port);
> -	if (err)
> -		return err;
> +	port->variant = of_device_get_match_data(dev);
> +
> +	if (port->variant->version != CPM5NC_HOST) {
> +		err = xilinx_cpm_pcie_init_irq_domain(port);

  xilinx_cpm_pcie_init_port()
  {
    if (variant->version != CPM5NC_HOST)
      return;
    ...

  xilinx_cpm_pcie_probe()
  {
    ...
    if (port->variant->version != CPM5NC_HOST) {
      err = xilinx_cpm_pcie_init_irq_domain(port);
    ...
    xilinx_cpm_pcie_init_port();
    ...
    if (port->variant->version != CPM5NC_HOST) {
      err = xilinx_cpm_setup_irq(port);
    ...
  err_host_bridge:
    if (port->variant->version != CPM5NC_HOST)
      xilinx_cpm_free_interrupts(port);
    ...
  err_free_irq_domains:
    if (port->variant->version != CPM5NC_HOST)
      xilinx_cpm_free_irq_domains(port);

Right now one CPM5NC_HOST test is inside xilinx_cpm_pcie_init_port()
all the others are in xilinx_cpm_pcie_probe().

I think it would be nicer if the tests were inside
xilinx_cpm_pcie_init_irq_domain(), xilinx_cpm_setup_irq(),
xilinx_cpm_free_interrupts(), and xilinx_cpm_free_irq_domains() so
they're all done the same way and they're closer to the actual
differences instead of cluttering xilinx_cpm_pcie_probe().

Also, this makes it look like CPM5NC_HOST doesn't support any
interrupts at all.  No INTx, no MSI, no MSI-X.  Is that true?  If so,
what good is a host controller where interrupts don't work?

Bjorn