linux-kernel - Re: [PATCH v8 2/9] PCI: stm32: Add PCIe host support for STM32MP25

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Message-ID: <c01d0d72-e43c-4e10-b298-c8ed4f5d1942@foss.st.com>
Date: Mon, 12 May 2025 17:08:13 +0200
From: Christian Bruel <christian.bruel@...s.st.com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
CC: <lpieralisi@...nel.org>, <kw@...ux.com>, <robh@...nel.org>,
        <bhelgaas@...gle.com>, <krzk+dt@...nel.org>, <conor+dt@...nel.org>,
        <mcoquelin.stm32@...il.com>, <alexandre.torgue@...s.st.com>,
        <p.zabel@...gutronix.de>, <thippeswamy.havalige@....com>,
        <shradha.t@...sung.com>, <quic_schintav@...cinc.com>,
        <cassel@...nel.org>, <johan+linaro@...nel.org>,
        <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 2/9] PCI: stm32: Add PCIe host support for STM32MP25

Hi Manivannan,

On 4/30/25 09:30, Manivannan Sadhasivam wrote:
> On Wed, Apr 23, 2025 at 11:01:12AM +0200, Christian Bruel wrote:
>> Add driver for the STM32MP25 SoC PCIe Gen1 2.5 GT/s and Gen2 5GT/s
>> controller based on the DesignWare PCIe core.
>>
>> Supports MSI via GICv2m, Single Virtual Channel, Single Function
>>
>> Supports WAKE# GPIO.
>>
> 
> Mostly looks good. Just a couple of comments below.
> 
>> Signed-off-by: Christian Bruel <christian.bruel@...s.st.com>
>> ---
>>   drivers/pci/controller/dwc/Kconfig      |  12 +
>>   drivers/pci/controller/dwc/Makefile     |   1 +
>>   drivers/pci/controller/dwc/pcie-stm32.c | 368 ++++++++++++++++++++++++
>>   drivers/pci/controller/dwc/pcie-stm32.h |  15 +
>>   4 files changed, 396 insertions(+)
>>   create mode 100644 drivers/pci/controller/dwc/pcie-stm32.c
>>   create mode 100644 drivers/pci/controller/dwc/pcie-stm32.h
>>
> 
> [...]
> 
>> +static int stm32_pcie_probe(struct platform_device *pdev)
>> +{
>> +	struct stm32_pcie *stm32_pcie;
>> +	struct device *dev = &pdev->dev;
>> +	int ret;
>> +
>> +	stm32_pcie = devm_kzalloc(dev, sizeof(*stm32_pcie), GFP_KERNEL);
>> +	if (!stm32_pcie)
>> +		return -ENOMEM;
>> +
>> +	stm32_pcie->pci.dev = dev;
>> +	stm32_pcie->pci.ops = &dw_pcie_ops;
>> +	stm32_pcie->pci.pp.ops = &stm32_pcie_host_ops;
>> +
>> +	stm32_pcie->regmap = syscon_regmap_lookup_by_compatible("st,stm32mp25-syscfg");
>> +	if (IS_ERR(stm32_pcie->regmap))
>> +		return dev_err_probe(dev, PTR_ERR(stm32_pcie->regmap),
>> +				     "No syscfg specified\n");
>> +
>> +	stm32_pcie->clk = devm_clk_get(dev, NULL);
>> +	if (IS_ERR(stm32_pcie->clk))
>> +		return dev_err_probe(dev, PTR_ERR(stm32_pcie->clk),
>> +				     "Failed to get PCIe clock source\n");
>> +
>> +	stm32_pcie->rst = devm_reset_control_get_exclusive(dev, NULL);
>> +	if (IS_ERR(stm32_pcie->rst))
>> +		return dev_err_probe(dev, PTR_ERR(stm32_pcie->rst),
>> +				     "Failed to get PCIe reset\n");
>> +
>> +	ret = stm32_pcie_parse_port(stm32_pcie);
>> +	if (ret)
>> +		return ret;
>> +
>> +	platform_set_drvdata(pdev, stm32_pcie);
>> +
>> +	ret = pm_runtime_set_active(dev);
>> +	if (ret < 0) {
>> +		dev_err(dev, "Failed to activate runtime PM %d\n", ret);
> 
> Please use dev_err_probe() here and below.

OK, will report this in the EP driver also.

> 
>> +		return ret;
>> +	}
>> +
>> +	ret = devm_pm_runtime_enable(dev);
>> +	if (ret < 0) {
>> +		dev_err(dev, "Failed to enable runtime PM %d\n", ret);
>> +		return ret;
>> +	}
>> +
>> +	pm_runtime_get_noresume(dev);
>> +
> 
> I know that a lot of the controller drivers do this for no obvious reason. But
> in this case, I believe you want to enable power domain or genpd before
> registering the host bridge. Is that right? 

We call pm_runtime_enable() before stm32_add_pcie_port() and 
dw_pcie_host_init(). This ensures that PCIe is active during the PERST# 
sequence and before accessing the DWC registers.

 > And the fact that you are not
> decrementing the runtime usage count means, you want to keep it ON all the time?
> Beware that your system suspend/resume calls would never get executed.

We do not support PM runtime autosuspend, so we must notify PM runtime 
that PCIe is always active. Without invoking pm_runtime_get_noresume(), 
PCIe would mistakenly be marked as suspended.
The function stm32_pcie_suspend_noirq() is triggered when the system 
transitions to Stop or Standby power states, (from /sys/power/state)

> 
> Also in any case, you need to call this before devm_pm_runtime_enable().
> Otherwise, PM core will suspend the parent and enable it during
> pm_runtime_get_noresume(), which is redundant.

OK, I will invert the calls.

Thank you

Christian

> 
> - Mani
>