Re: [PATCH V13 12/12] PCI: tegra: Add Tegra194 PCIe support

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Tue, Jul 23, 2019 at 08:14:08PM +0530, Vidya Sagar wrote:
> On 7/16/2019 4:52 PM, Lorenzo Pieralisi wrote:
> > On Sat, Jul 13, 2019 at 12:34:34PM +0530, Vidya Sagar wrote:
> > 
> > [...]
> > 
> > > > > > > +static int tegra_pcie_bpmp_set_ctrl_state(struct tegra_pcie_dw *pcie,
> > > > > > > +					  bool enable)
> > > > > > > +{
> > > > > > > +	struct mrq_uphy_response resp;
> > > > > > > +	struct tegra_bpmp_message msg;
> > > > > > > +	struct mrq_uphy_request req;
> > > > > > > +	int err;
> > > > > > > +
> > > > > > > +	if (pcie->cid == 5)
> > > > > > > +		return 0;
> > > > > > 
> > > > > > What's wrong with cid == 5 ? Explain please.
> > > > > Controller with ID=5 doesn't need any programming to enable it which is
> > > > > done here through calling firmware API.
> > > > > 
> > > > > > 
> > > > > > > +	memset(&req, 0, sizeof(req));
> > > > > > > +	memset(&resp, 0, sizeof(resp));
> > > > > > > +
> > > > > > > +	req.cmd = CMD_UPHY_PCIE_CONTROLLER_STATE;
> > > > > > > +	req.controller_state.pcie_controller = pcie->cid;
> > > > > > > +	req.controller_state.enable = enable;
> > > > > > > +
> > > > > > > +	memset(&msg, 0, sizeof(msg));
> > > > > > > +	msg.mrq = MRQ_UPHY;
> > > > > > > +	msg.tx.data = &req;
> > > > > > > +	msg.tx.size = sizeof(req);
> > > > > > > +	msg.rx.data = &resp;
> > > > > > > +	msg.rx.size = sizeof(resp);
> > > > > > > +
> > > > > > > +	if (irqs_disabled())
> > > > > > 
> > > > > > Can you explain to me what this check is meant to achieve please ?
> > > > > Firmware interface provides different APIs to be called when there are
> > > > > no interrupts enabled in the system (noirq context) and otherwise
> > > > > hence checking that situation here and calling appropriate API.
> > > > 
> > > > That's what I am questioning. Being called from {suspend/resume}_noirq()
> > > > callbacks (if that's the code path this check caters for) does not mean
> > > > irqs_disabled() == true.
> > > Agree.
> > > Actually, I got a hint of having this check from the following.
> > > Both tegra_bpmp_transfer_atomic() and tegra_bpmp_transfer() are indirectly
> > > called by APIs registered with .master_xfer() and .master_xfer_atomic() hooks of
> > > struct i2c_algorithm and the decision to call which one of these is made using the
> > > following check in i2c-core.h file.
> > > static inline bool i2c_in_atomic_xfer_mode(void)
> > > {
> > > 	return system_state > SYSTEM_RUNNING && irqs_disabled();
> > > }
> > > I think I should use this condition as is IIUC.
> > > Please let me know if there are any concerns with this.
> > 
> > It is not a concern, it is just that I don't understand how this code
> > can be called with IRQs disabled, if you can give me an execution path I
> > am happy to leave the check there. On top of that, when called from
> > suspend NOIRQ context, it is likely to use the blocking API (because
> > IRQs aren't disabled at CPU level) behind which there is most certainly
> > an IRQ required to wake the thread up and if the IRQ in question was
> > disabled in the suspend NOIRQ phase this code is likely to deadlock.
> > 
> > I want to make sure we can justify adding this check, I do not
> > want to add it because we think it can be needed when it may not
> > be needed at all (and it gets copy and pasted over and over again
> > in other drivers).
> I had a discussion internally about this and the prescribed usage of these APIs
> seem to be that
> use tegra_bpmp_transfer() in .probe() and other paths where interrupts are
> enabled as this API needs interrupts to be enabled for its working.
> Use tegra_bpmp_transfer_atomic() surrounded by local_irq_save()/local_irq_restore()
> in other paths where interrupt servicing is disabled.

Why tegra_bpmp_transfer_atomic() needs IRQs to be disabled ? And why
is it needed in this piece of code where IRQs are _never_ disabled
at CPU level ?

IRQs are enabled when you call a suspend_noirq() callback, so the
blocking API can be used as long as the IRQ descriptor backing
the IRQ that will wake-up the blocked call is marked as
IRQF_NO_SUSPEND.

The problem is not IRQs enabled/disabled at CPU level, the problem is
the IRQ descriptor of the IRQ required to handle the blocking BPMP call,
mark it as IRQF_NO_SUSPEND and remove the tegra_bpmp_transfer_atomic()
call from this code (or please give me a concrete example pinpointing
why it is needed).

Thanks,
Lorenzo

> I'll go ahead and make next patch series with this if this looks fine to you.
> 
> > 
> > > > Actually, if tegra_bpmp_transfer() requires IRQs to be enabled you may
> > > > even end up in a situation where that blocking call does not wake up
> > > > because the IRQ in question was disabled in the NOIRQ suspend/resume
> > > > phase.
> > > > 
> > > > [...]
> > > > 
> > > > > > > +static int tegra_pcie_dw_probe(struct platform_device *pdev)
> > > > > > > +{
> > > > > > > +	const struct tegra_pcie_soc *data;
> > > > > > > +	struct device *dev = &pdev->dev;
> > > > > > > +	struct resource *atu_dma_res;
> > > > > > > +	struct tegra_pcie_dw *pcie;
> > > > > > > +	struct resource *dbi_res;
> > > > > > > +	struct pcie_port *pp;
> > > > > > > +	struct dw_pcie *pci;
> > > > > > > +	struct phy **phys;
> > > > > > > +	char *name;
> > > > > > > +	int ret;
> > > > > > > +	u32 i;
> > > > > > > +
> > > > > > > +	pcie = devm_kzalloc(dev, sizeof(*pcie), GFP_KERNEL);
> > > > > > > +	if (!pcie)
> > > > > > > +		return -ENOMEM;
> > > > > > > +
> > > > > > > +	pci = &pcie->pci;
> > > > > > > +	pci->dev = &pdev->dev;
> > > > > > > +	pci->ops = &tegra_dw_pcie_ops;
> > > > > > > +	pp = &pci->pp;
> > > > > > > +	pcie->dev = &pdev->dev;
> > > > > > > +
> > > > > > > +	data = (struct tegra_pcie_soc *)of_device_get_match_data(dev);
> > > > > > > +	if (!data)
> > > > > > > +		return -EINVAL;
> > > > > > > +	pcie->mode = (enum dw_pcie_device_mode)data->mode;
> > > > > > > +
> > > > > > > +	ret = tegra_pcie_dw_parse_dt(pcie);
> > > > > > > +	if (ret < 0) {
> > > > > > > +		dev_err(dev, "Failed to parse device tree: %d\n", ret);
> > > > > > > +		return ret;
> > > > > > > +	}
> > > > > > > +
> > > > > > > +	pcie->pex_ctl_supply = devm_regulator_get(dev, "vddio-pex-ctl");
> > > > > > > +	if (IS_ERR(pcie->pex_ctl_supply)) {
> > > > > > > +		dev_err(dev, "Failed to get regulator: %ld\n",
> > > > > > > +			PTR_ERR(pcie->pex_ctl_supply));
> > > > > > > +		return PTR_ERR(pcie->pex_ctl_supply);
> > > > > > > +	}
> > > > > > > +
> > > > > > > +	pcie->core_clk = devm_clk_get(dev, "core");
> > > > > > > +	if (IS_ERR(pcie->core_clk)) {
> > > > > > > +		dev_err(dev, "Failed to get core clock: %ld\n",
> > > > > > > +			PTR_ERR(pcie->core_clk));
> > > > > > > +		return PTR_ERR(pcie->core_clk);
> > > > > > > +	}
> > > > > > > +
> > > > > > > +	pcie->appl_res = platform_get_resource_byname(pdev, IORESOURCE_MEM,
> > > > > > > +						      "appl");
> > > > > > > +	if (!pcie->appl_res) {
> > > > > > > +		dev_err(dev, "Failed to find \"appl\" region\n");
> > > > > > > +		return PTR_ERR(pcie->appl_res);
> > > > > > > +	}
> > > > > > > +	pcie->appl_base = devm_ioremap_resource(dev, pcie->appl_res);
> > > > > > > +	if (IS_ERR(pcie->appl_base))
> > > > > > > +		return PTR_ERR(pcie->appl_base);
> > > > > > > +
> > > > > > > +	pcie->core_apb_rst = devm_reset_control_get(dev, "apb");
> > > > > > > +	if (IS_ERR(pcie->core_apb_rst)) {
> > > > > > > +		dev_err(dev, "Failed to get APB reset: %ld\n",
> > > > > > > +			PTR_ERR(pcie->core_apb_rst));
> > > > > > > +		return PTR_ERR(pcie->core_apb_rst);
> > > > > > > +	}
> > > > > > > +
> > > > > > > +	phys = devm_kcalloc(dev, pcie->phy_count, sizeof(*phys), GFP_KERNEL);
> > > > > > > +	if (!phys)
> > > > > > > +		return PTR_ERR(phys);
> > > > > > > +
> > > > > > > +	for (i = 0; i < pcie->phy_count; i++) {
> > > > > > > +		name = kasprintf(GFP_KERNEL, "p2u-%u", i);
> > > > > > > +		if (!name) {
> > > > > > > +			dev_err(dev, "Failed to create P2U string\n");
> > > > > > > +			return -ENOMEM;
> > > > > > > +		}
> > > > > > > +		phys[i] = devm_phy_get(dev, name);
> > > > > > > +		kfree(name);
> > > > > > > +		if (IS_ERR(phys[i])) {
> > > > > > > +			ret = PTR_ERR(phys[i]);
> > > > > > > +			dev_err(dev, "Failed to get PHY: %d\n", ret);
> > > > > > > +			return ret;
> > > > > > > +		}
> > > > > > > +	}
> > > > > > > +
> > > > > > > +	pcie->phys = phys;
> > > > > > > +
> > > > > > > +	dbi_res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "dbi");
> > > > > > > +	if (!dbi_res) {
> > > > > > > +		dev_err(dev, "Failed to find \"dbi\" region\n");
> > > > > > > +		return PTR_ERR(dbi_res);
> > > > > > > +	}
> > > > > > > +	pcie->dbi_res = dbi_res;
> > > > > > > +
> > > > > > > +	pci->dbi_base = devm_ioremap_resource(dev, dbi_res);
> > > > > > > +	if (IS_ERR(pci->dbi_base))
> > > > > > > +		return PTR_ERR(pci->dbi_base);
> > > > > > > +
> > > > > > > +	/* Tegra HW locates DBI2 at a fixed offset from DBI */
> > > > > > > +	pci->dbi_base2 = pci->dbi_base + 0x1000;
> > > > > > > +
> > > > > > > +	atu_dma_res = platform_get_resource_byname(pdev, IORESOURCE_MEM,
> > > > > > > +						   "atu_dma");
> > > > > > > +	if (!atu_dma_res) {
> > > > > > > +		dev_err(dev, "Failed to find \"atu_dma\" region\n");
> > > > > > > +		return PTR_ERR(atu_dma_res);
> > > > > > > +	}
> > > > > > > +	pcie->atu_dma_res = atu_dma_res;
> > > > > > > +	pci->atu_base = devm_ioremap_resource(dev, atu_dma_res);
> > > > > > > +	if (IS_ERR(pci->atu_base))
> > > > > > > +		return PTR_ERR(pci->atu_base);
> > > > > > > +
> > > > > > > +	pcie->core_rst = devm_reset_control_get(dev, "core");
> > > > > > > +	if (IS_ERR(pcie->core_rst)) {
> > > > > > > +		dev_err(dev, "Failed to get core reset: %ld\n",
> > > > > > > +			PTR_ERR(pcie->core_rst));
> > > > > > > +		return PTR_ERR(pcie->core_rst);
> > > > > > > +	}
> > > > > > > +
> > > > > > > +	pp->irq = platform_get_irq_byname(pdev, "intr");
> > > > > > > +	if (!pp->irq) {
> > > > > > > +		dev_err(dev, "Failed to get \"intr\" interrupt\n");
> > > > > > > +		return -ENODEV;
> > > > > > > +	}
> > > > > > > +
> > > > > > > +	ret = devm_request_irq(dev, pp->irq, tegra_pcie_irq_handler,
> > > > > > > +			       IRQF_SHARED, "tegra-pcie-intr", pcie);
> > > > > > > +	if (ret) {
> > > > > > > +		dev_err(dev, "Failed to request IRQ %d: %d\n", pp->irq, ret);
> > > > > > > +		return ret;
> > > > > > > +	}
> > > > > > > +
> > > > > > > +	pcie->bpmp = tegra_bpmp_get(dev);
> > > > > > > +	if (IS_ERR(pcie->bpmp))
> > > > > > > +		return PTR_ERR(pcie->bpmp);
> > > > > > > +
> > > > > > > +	platform_set_drvdata(pdev, pcie);
> > > > > > > +
> > > > > > > +	if (pcie->mode == DW_PCIE_RC_TYPE) {
> > > > > > > +		ret = tegra_pcie_config_rp(pcie);
> > > > > > > +		if (ret && ret != -ENOMEDIUM)
> > > > > > > +			goto fail;
> > > > > > > +		else
> > > > > > > +			return 0;
> > > > > > 
> > > > > > So if the link is not up we still go ahead and make probe
> > > > > > succeed. What for ?
> > > > > We may need root port to be available to support hot-plugging of
> > > > > endpoint devices, so, we don't fail the probe.
> > > > 
> > > > We need it or we don't. If you do support hotplugging of endpoint
> > > > devices point me at the code, otherwise link up failure means
> > > > failure to probe.
> > > Currently hotplugging of endpoint is not supported, but it is one of
> > > the use cases that we may add support for in future.
> > 
> > You should elaborate on this, I do not understand what you mean,
> > either the root port(s) supports hotplug or it does not.
> > 
> > > But, why should we fail probe if link up doesn't happen? As such,
> > > nothing went wrong in terms of root port initialization right?  I
> > > checked other DWC based implementations and following are not failing
> > > the probe pci-dra7xx.c, pcie-armada8k.c, pcie-artpec6.c, pcie-histb.c,
> > > pcie-kirin.c, pcie-spear13xx.c, pci-exynos.c, pci-imx6.c,
> > > pci-keystone.c, pci-layerscape.c
> > > 
> > > Although following do fail the probe if link is not up.  pcie-qcom.c,
> > > pcie-uniphier.c, pci-meson.c
> > > 
> > > So, to me, it looks more like a choice we can make whether to fail the
> > > probe or not and in this case we are choosing not to fail.
> > 
> > I disagree. I had an offline chat with Bjorn and whether link-up should
> > fail the probe or not depends on whether the root port(s) is hotplug
> > capable or not and this in turn relies on the root port "Slot
> > implemented" bit in the PCI Express capabilities register.
> > 
> > It is a choice but it should be based on evidence.
> > 
> > Lorenzo
> With Bjorn's latest comment on top of this, I think we are good not to fail
> the probe here.
> 
> - Vidya Sagar
> > 
>