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

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Tue, Jul 16, 2024 at 09:54:54AM +0530, Krishna Chaitanya Chundru wrote:
> 
> 
> On 7/16/2024 9:48 AM, Manivannan Sadhasivam wrote:
> > 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@linaro.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@linaro.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
> I leaved a gap between bridge-> & bus by mistake, I want to highlight
> bridge->bus in above comment. The bus can be NULL and it can create NULL
> point access.

How can the bridge->bus be NULL? Only if the bridge itself is not enumerated, it
will be NULL. And that cannot happen unless something wrong with the controller
itself. In that case, how can Link up event be generated?

- Mani

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