Re: [PATCH v2 07/10] ARM: tegra: pcie: Add device tree support

[Stephen Warren <swarren@wwwdotorg.org>]

On 06/12/2012 12:21 AM, Thierry Reding wrote:
> * Stephen Warren wrote:
>> On 06/11/2012 09:05 AM, Thierry Reding wrote:
>>> This commit adds support for instantiating the Tegra PCIe
>>> controller from a device tree.
>> 
>>> +++ b/Documentation/devicetree/bindings/pci/tegra-pcie.txt
>> 
>> Can we please name this nvidia,tegra20-pcie.txt to match the
>> naming of all the other Tegra bindings.
> 
> Yes, will do.
> 
>>> +Required properties: +- compatible: "nvidia,tegra20-pcie" +-
>>> reg: physical base address and length of the controller's
>>> registers
>> 
>> Since there's more than one range now, that should specify how
>> many entries are required and what they represent.
> 
> Okay.
> 
>>> +Optional properties: +- pex-clk-supply: supply voltage for
>>> internal reference clock +- vdd-supply: power supply for
>>> controller (1.05V)
>> 
>> Those shouldn't be optional. If the board has no regulator, the
>> board's .dts should provide a fixed always-on regulator that
>> those properties can refer to, so that the driver can always
>> get() those regulators.
> 
> That'll add more dummy regulators and I don't think sprinkling them
> across the DTS is going to work very well. Maybe collecting them
> under a top-level "regulators" node is a good option. If you have a
> better alternative, I'm all open for it.
> 
>>> diff --git a/arch/arm/boot/dts/tegra20.dtsi
>>> b/arch/arm/boot/dts/tegra20.dtsi
>> 
>>> +	pci {
>> ...
>>> +		status = "disable";
>> 
>> That should be "disabled"; sorry for providing a bad example.
> 
> Yes.
> 
>>> diff --git a/arch/arm/mach-tegra/pcie.c
>>> b/arch/arm/mach-tegra/pcie.c
>> 
>>> +static struct tegra_pcie_pdata *tegra_pcie_parse_dt(struct
>>> platform_device *pdev)
>> 
>>> +	if (of_find_property(node, "vdd-supply", NULL)) {
>> 
>> As mentioned above, that if statement should be removed, since
>> the regulators shouldn't be optional.
> 
> Okay.
> 
>>> +		pcie->vdd_supply = regulator_get(&pdev->dev, "vdd");
>> 
>> Those could be devm_regulator_get(). Then tegra_pcie_remove()
>> wouldn't have to put() them.
> 
> Okay.
> 
>>> +	for (i = 0; i < TEGRA_PCIE_MAX_PORTS; i++) +
>>> pdata->enable_ports[i] = true;
>> 
>> Shouldn't the DT indicate which ports are used? I assume there's
>> some reason that the existing driver allows that to be
>> configured, rather than always enabling all ports. At least,
>> enumeration time wasted on non-existent ports springs to mind,
>> and perhaps attempting to enable port 1 when port 0 is x4 and
>> using all the lanes would cause errors in port 0?
> 
> Yes, that's been on my mind as well. I'm not sure about the best
> binding for this. Perhaps something like:
> 
> pci { enable-ports = <0 1 2>; };
> 
> Would do?

That seems reasonable, although since the property is presumably
something specific to the Tegra PCIe binding, not generic, I think it
should be nvidia,enable-ports.