Date:   Mon, 5 Aug 2019 22:24:42 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:     <bhelgaas@...gle.com>, <robh+dt@...nel.org>,
        <mark.rutland@....com>, <thierry.reding@...il.com>,
        <jonathanh@...dia.com>, <kishon@...com>, <catalin.marinas@....com>,
        <will.deacon@....com>, <jingoohan1@...il.com>,
        <gustavo.pimentel@...opsys.com>, <digetx@...il.com>,
        <mperttunen@...dia.com>, <linux-pci@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <kthota@...dia.com>,
        <mmaddireddy@...dia.com>, <sagar.tv@...il.com>
Subject: Re: [PATCH V13 12/12] PCI: tegra: Add Tegra194 PCIe support

On 8/5/2019 7:31 PM, Lorenzo Pieralisi wrote:
> On Fri, Aug 02, 2019 at 05:36:43PM +0530, Vidya Sagar wrote:
>> On 7/30/2019 9:19 PM, Lorenzo Pieralisi wrote:
>>> 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).
>> Ideally, using tegra_bpmp_transfer() alone in all paths (.probe() as
>> well as .resume_noirq()) should have worked as the corresponding IRQ
>> is already flagged as IRQF_NO_SUSPEND, but, because of the way BPMP-FW
>> driver in kernel making its interface available through
>> .resume_early(), tegra_bpmp_transfer() wasn't working as expected and
>> I pushed a patch (CC'ing you) at
>> http://patchwork.ozlabs.org/patch/1140973/ to make it .resume_noirq()
>> from .resume_early().  With that in place, we can just use
>> tegra_bpmp_trasnfer().  I'll push a new patch with this change once my
>> BPMP-FW driver patch is approved.
> 
> Does this leave you with a resume_noirq() callbacks ordering issue to
> sort out ?
Not really.

> 
> a.k.a How will you guarantee that the BPMP will resume before the host
> bridge ?
It is already taken care of in the following way.
PCIe controller's device-tree node has an entry with a phandle of BPMP-FW's node
to get a handle of it and PCIe driver uses tegra_bpmp_get() API for that.
This API returns -EPROBE_DEFER if BPMP-FW's driver is not ready yet, which guarantees
that PCIe driver gets loaded only after BPMP-FW's driver and this order is followed
during noirq phase also.

> 
> Thanks,
> Lorenzo
> 
>> Thanks,
>> Vidya Sagar
>>>
>>> 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
>>>>>
>>>>
>>

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