linux-kernel - Re: [PATCH v2] pcie: Add Xilinx PCIe Host Bridge IP driver

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Date:	Mon, 3 Mar 2014 10:43:25 -0700
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Srikanth Thokala <sthokal@...inx.com>
Cc:	bhelgaas@...gle.com, michal.simek@...inx.com,
	grant.likely@...aro.org, robh+dt@...nel.org,
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2] pcie: Add Xilinx PCIe Host Bridge IP driver

On Mon, Mar 03, 2014 at 07:10:36PM +0530, Srikanth Thokala wrote:

> +Required properties:
> +- #address-cells: Address representation for root ports, set to <3>
> +- #size-cells: Size representation for root ports, set to <2>
> +- compatible: Should contain "xlnx,axi-pcie-host-1.00.a"
> +- reg: Should contain AXI PCIe registers location and length
> +- interrupts: Should contain AXI PCIe interrupt
> +- ranges: ranges for the PCI memory regions
> +	Please refer to the standard PCI bus binding document for a more
> +	detailed explanation
> +
> +Example:
> +++++++++
> +
> +	pci_express: axi-pcie@...00000 {
> +		#address-cells = <3>;
> +		#size-cells = <2>;
> +		compatible = "xlnx,axi-pcie-host-1.00.a";
> +		reg = < 0x50000000 0x10000000 >;
> +		interrupts = < 0 52 4 >;
> +		ranges = < 0x02000000 0 0x60000000 0x60000000 0 0x10000000 >;
> +	};

That is much shorter, more notes:
 - It looks like the driver (HW?) has no support for IO space?
 - How are INTA/B/C/D handled? Typically I'd like to see an
   interrupt-mapping block describing them.

   There are a few options here, if the HW can decode A/B/C/D then
   it probably needs another irq_domain for INTx, and have the IRQ
   handler decode like it does for MSI.
- The stanza needs a
    device_type = "pci";

> +	for (i = 0; i < port->mem_resno; i++)
> +		pci_add_resource_offset(&sys->resources, &port->mem[i],
> +					sys->mem_offset);

The sys->mem_offset is probably wrong, please review Arnd's comments
on the recent threads with Will and Liviu regarding how this is
supposed to work with DT.

You may want to work with Liviu to use his patch set which provides
more generic support. Also, the driver needs to put every one of these
ports in a PCI domain, Liviu is working on generic support for that
too.

> +static struct pci_bus __init *xilinx_pcie_scan_bus(int nr,
> +				struct pci_sys_data *sys)
> +{
> +	struct xilinx_pcie_port *port = sys_to_pcie(sys);
> +	struct pci_bus *bus;
> +
> +	if (port) {
> +		port->root_busno = sys->busnr;
> +		bus = pci_scan_root_bus(NULL, sys->busnr, &xilinx_pcie_ops,
> +					sys, &sys->resources);

The NULL is probably wrong, please review the recent thread with Lucas
and Jingoo 'PCI irq mapping fixes and cleanups'

> +static int xilinx_pcie_map_irq(const struct pci_dev *dev, u8 slot, u8 pin)
> +{
> +	struct xilinx_pcie_port *port = sys_to_pcie(dev->bus->sysdata);
> +
> +	if (!port)
> +		return -EINVAL;
> +
> +	return port->irq;
> +}

It is preferred to use DT mechanisms via of_irq_parse_and_map_pci
(interrupt-mapping, etc) to define the slot IRQ, drivers should not
provide a map_irq unless absolutely necessary.

> +	/* make sure it is root port before touching header */
> +	pcie_write(port, PCI_COMMAND_MASTER, PCI_COMMAND);

Bit of a confusing comment

> +	/* Check if PCIe link is up? */
> +	port->link_up = xilinx_pcie_is_link_up(port);
> +	if (!port->link_up)
> +		dev_info(port->dev, "PCIe Link is DOWN\n");
> +	else
> +		dev_info(port->dev, "PCIe Link is UP\n");

Don't forget to think about hot plug

> +	/* Register Interrupt Handler */
> +	err = request_irq(port->irq, xilinx_pcie_intr_handler,
> +				IRQF_SHARED, "xilinx-pcie", port);

Use devm? This is leaking on error cases.

Review other resources too...

> +	/* Request and map I/O memory */
> +	io = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	port->phys_reg_base = io->start;
> +	port->reg_size = resource_size(io);

Here it uses the platform resource..

> +	/* Map the IRQ */
> +	port->irq = irq_of_parse_and_map(node, 0);

.. And here it doesn't, probably should be consistent and just use the
platform resources.

Jason
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