linux-kernel - Re: [PATCH 13/14] PCI: qcom: Simulate PCIe hotplug using 'global' interrupt

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Message-ID: <20240716041827.GD3446@thinkpad>
Date: Tue, 16 Jul 2024 09:48:27 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>, linux-pci@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH 13/14] PCI: qcom: Simulate PCIe hotplug using 'global'
 interrupt

On Tue, Jul 16, 2024 at 09:34:13AM +0530, Krishna Chaitanya Chundru wrote:
> 
> 
> On 7/15/2024 11:03 PM, Manivannan Sadhasivam via B4 Relay wrote:
> > From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > 
> > Historically, Qcom PCIe RC controllers lack standard hotplug support. So
> > when an endpoint is attached to the SoC, users have to rescan the bus
> > manually to enumerate the device. But this can be avoided by simulating the
> > PCIe hotplug using Qcom specific way.
> > 
> > Qcom PCIe RC controllers are capable of generating the 'global' SPI
> > interrupt to the host CPUs. The device driver can use this event to
> > identify events such as PCIe link specific events, safety events etc...
> > 
> > One such event is the PCIe Link up event generated when an endpoint is
> > detected on the bus and the Link is 'up'. This event can be used to
> > simulate the PCIe hotplug in the Qcom SoCs.
> > 
> > So add support for capturing the PCIe Link up event using the 'global'
> > interrupt in the driver. Once the Link up event is received, the bus
> > underneath the host bridge is scanned to enumerate PCIe endpoint devices,
> > thus simulating hotplug.
> > 
> > All of the Qcom SoCs have only one rootport per controller instance. So
> > only a single 'Link up' event is generated for the PCIe controller.
> > 
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > ---
> >   drivers/pci/controller/dwc/pcie-qcom.c | 55 ++++++++++++++++++++++++++++++++++
> >   1 file changed, 55 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > index 0180edf3310e..38ed411d2052 100644
> > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> > @@ -50,6 +50,9 @@
> >   #define PARF_AXI_MSTR_WR_ADDR_HALT_V2		0x1a8
> >   #define PARF_Q2A_FLUSH				0x1ac
> >   #define PARF_LTSSM				0x1b0
> > +#define PARF_INT_ALL_STATUS			0x224
> > +#define PARF_INT_ALL_CLEAR			0x228
> > +#define PARF_INT_ALL_MASK			0x22c
> >   #define PARF_SID_OFFSET				0x234
> >   #define PARF_BDF_TRANSLATE_CFG			0x24c
> >   #define PARF_SLV_ADDR_SPACE_SIZE		0x358
> > @@ -121,6 +124,9 @@
> >   /* PARF_LTSSM register fields */
> >   #define LTSSM_EN				BIT(8)
> > +/* PARF_INT_ALL_{STATUS/CLEAR/MASK} register fields */
> > +#define PARF_INT_ALL_LINK_UP			BIT(13)
> > +
> >   /* PARF_NO_SNOOP_OVERIDE register fields */
> >   #define WR_NO_SNOOP_OVERIDE_EN			BIT(1)
> >   #define RD_NO_SNOOP_OVERIDE_EN			BIT(3)
> > @@ -260,6 +266,7 @@ struct qcom_pcie {
> >   	struct icc_path *icc_cpu;
> >   	const struct qcom_pcie_cfg *cfg;
> >   	struct dentry *debugfs;
> > +	int global_irq;
> >   	bool suspended;
> >   };
> > @@ -1488,6 +1495,29 @@ static void qcom_pcie_init_debugfs(struct qcom_pcie *pcie)
> >   				    qcom_pcie_link_transition_count);
> >   }
> > +static irqreturn_t qcom_pcie_global_irq_thread(int irq, void *data)
> > +{
> > +	struct qcom_pcie *pcie = data;
> > +	struct dw_pcie_rp *pp = &pcie->pci->pp; > +	struct device *dev = pcie->pci->dev;
> > +	u32 status = readl_relaxed(pcie->parf + PARF_INT_ALL_STATUS);
> > +
> > +	writel_relaxed(status, pcie->parf + PARF_INT_ALL_CLEAR);
> > +
> > +	if (FIELD_GET(PARF_INT_ALL_LINK_UP, status)) {
> > +		dev_dbg(dev, "Received Link up event. Starting enumeration!\n");
> > +		/* Rescan the bus to enumerate endpoint devices */
> > +		pci_lock_rescan_remove();
> > +		pci_rescan_bus(pp->bridge->bus);
> There can be chances of getting link up interrupt before PCIe framework
> starts enumeration and at that time bridge-> bus is not created and
> cause NULL point access.
> Please have a check for this.
> 

Host bridge is enumerated during dw_pcie_host_init() and the IRQ handler is
registered afterwards. So there is no way the 'pp->bridge' can be NULL.

- Mani

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