Re: [PATCH v6 8/9] PCI: pwrctrl: Add power control driver for tc9563

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Aug 28, 2025 at 05:39:05PM +0530, Krishna Chaitanya Chundru wrote:
> TC9563 is a PCIe switch which has one upstream and three downstream
> ports. To one of the downstream ports integrated ethernet MAC is connected
> as endpoint device. Other two downstream ports are supposed to connect to
> external device. One Host can connect to TC9563 by upstream port. TC9563
> switch needs to be configured after powering on and before the PCIe link
> was up.
> 
> The PCIe controller driver already enables link training at the host side
> even before this driver probe happens, due to this when driver enables
> power to the switch it participates in the link training and PCIe link
> may come up before configuring the switch through i2c. Once the link is
> up the configuration done through i2c will not have any affect.To prevent
> the host from participating in link training, disable link training on the
> host side to ensure the link does not come up before the switch is
> configured via I2C.

s/any affect/any effect/
s/.To prevent/. To prevent/

> Based up on dt property and type of the port, tc9563 is configured
> through i2c.

s/up on/on/

Pick "i2c" or "I2C" and use it consistently.

> +config PCI_PWRCTRL_TC9563
> +	tristate "PCI Power Control driver for TC9563 PCIe switch"
> +	select PCI_PWRCTRL
> +	help
> +	  Say Y here to enable the PCI Power Control driver of TC9563 PCIe
> +	  switch.
> +
> +	  This driver enables power and configures the TC9563 PCIe switch
> +	  through i2c.TC9563 is a PCIe switch which has one upstream and three
> +	  downstream ports. To one of the downstream ports integrated ethernet
> +	  MAC is connected as endpoint device. Other two downstream ports are
> +	  supposed to connect to external device.

s/i2c.TC9563/i2c. TC9563/

> +static int tc9563_pwrctrl_bring_up(struct tc9563_pwrctrl_ctx *ctx)
> +{
> +	struct tc9563_pwrctrl_cfg *cfg;
> +	int ret, i;
> +
> +	ret = regulator_bulk_enable(ARRAY_SIZE(ctx->supplies), ctx->supplies);
> +	if (ret < 0)
> +		return dev_err_probe(ctx->pwrctrl.dev, ret, "cannot enable regulators\n");
> +
> +	gpiod_set_value(ctx->reset_gpio, 0);
> +
> +	 /*
> +	  * From TC9563 PORSYS rev 0.2, figure 1.1 POR boot sequence
> +	  * wait for 10ms for the internal osc frequency to stabilize.
> +	  */
> +	usleep_range(10000, 10500);

Possible place for fsleep() unless you have a specific reason for the
+500us interval?

> +static int tc9563_pwrctrl_probe(struct platform_device *pdev)
> +{
> +	struct pci_host_bridge *bridge = to_pci_host_bridge(pdev->dev.parent);
> +	struct pci_dev *pci_dev = to_pci_dev(pdev->dev.parent);
> +	struct pci_bus *bus = bridge->bus;
> +	struct device *dev = &pdev->dev;
> +	enum tc9563_pwrctrl_ports port;
> +	struct tc9563_pwrctrl_ctx *ctx;
> +	struct device_node *i2c_node;
> +	int ret, addr;
> +
> +	ctx = devm_kzalloc(dev, sizeof(*ctx), GFP_KERNEL);
> +	if (!ctx)
> +		return -ENOMEM;
> +
> +	ret = of_property_read_u32_index(pdev->dev.of_node, "i2c-parent", 1, &addr);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to read i2c-parent property\n");
> +
> +	i2c_node = of_parse_phandle(dev->of_node, "i2c-parent", 0);
> +	ctx->adapter = of_find_i2c_adapter_by_node(i2c_node);
> +	of_node_put(i2c_node);
> +	if (!ctx->adapter)
> +		return dev_err_probe(dev, -EPROBE_DEFER, "Failed to find I2C adapter\n");
> +
> +	ctx->client = i2c_new_dummy_device(ctx->adapter, addr);
> +	if (IS_ERR(ctx->client)) {
> +		dev_err(dev, "Failed to create I2C client\n");
> +		i2c_put_adapter(ctx->adapter);
> +		return PTR_ERR(ctx->client);
> +	}
> +
> +	for (int i = 0; i < TC9563_PWRCTL_MAX_SUPPLY; i++)
> +		ctx->supplies[i].supply = tc9563_supply_names[i];
> +
> +	ret = devm_regulator_bulk_get(dev, TC9563_PWRCTL_MAX_SUPPLY, ctx->supplies);
> +	if (ret) {
> +		dev_err_probe(dev, ret,
> +			      "failed to get supply regulator\n");
> +		goto remove_i2c;
> +	}
> +
> +	ctx->reset_gpio = devm_gpiod_get(dev, "reset", GPIOD_OUT_HIGH);
> +	if (IS_ERR(ctx->reset_gpio)) {
> +		ret = dev_err_probe(dev, PTR_ERR(ctx->reset_gpio), "failed to get reset GPIO\n");
> +		goto remove_i2c;
> +	}
> +
> +	pci_pwrctrl_init(&ctx->pwrctrl, dev);
> +
> +	port = TC9563_USP;
> +	ret = tc9563_pwrctrl_parse_device_dt(ctx, pdev->dev.of_node, port);
> +	if (ret) {
> +		dev_err(dev, "failed to parse device tree properties: %d\n", ret);
> +		goto remove_i2c;
> +	}
> +
> +	/*
> +	 * Downstream ports are always children of the upstream port.
> +	 * The first node represents DSP1, the second node represents DSP2, and so on.
> +	 */
> +	for_each_child_of_node_scoped(pdev->dev.of_node, child) {
> +		ret = tc9563_pwrctrl_parse_device_dt(ctx, child, port++);
> +		if (ret)
> +			break;
> +		/* Embedded ethernet device are under DSP3 */
> +		if (port == TC9563_DSP3)
> +			for_each_child_of_node_scoped(child, child1) {
> +				ret = tc9563_pwrctrl_parse_device_dt(ctx, child1, port++);
> +				if (ret)
> +					break;
> +			}
> +	}
> +	if (ret) {
> +		dev_err(dev, "failed to parse device tree properties: %d\n", ret);
> +		goto remove_i2c;
> +	}
> +
> +	if (!pcie_link_is_active(pci_dev) && bridge->ops->stop_link)
> +		bridge->ops->stop_link(bus);

Is this pcie_link_is_active() test backwards?  Seems like you would
want to stop the link if it *is* active.

pcie_link_is_active() is racy, and this looks like a situation where
that could be an issue.  Would something break if you omitted the test
and *always* stopped and started the link here?

> +	ret = tc9563_pwrctrl_bring_up(ctx);
> +	if (ret)
> +		goto remove_i2c;
> +
> +	if (!pcie_link_is_active(pci_dev) && bridge->ops->start_link) {
> +		ret = bridge->ops->start_link(bus);
> +		if (ret)
> +			goto power_off;
> +	}
> +
> +	ret = devm_pci_pwrctrl_device_set_ready(dev, &ctx->pwrctrl);
> +	if (ret)
> +		goto power_off;
> +
> +	platform_set_drvdata(pdev, ctx);
> +
> +	return 0;
> +
> +power_off:
> +	tc9563_pwrctrl_power_off(ctx);
> +remove_i2c:
> +	i2c_unregister_device(ctx->client);
> +	i2c_put_adapter(ctx->adapter);
> +	return ret;
> +}