[PATCH 3/5] PCI: dwc: ep: Add a generic dw_pcie_ep_linkdown() API to handle Link Down event

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

As per the PCIe base spec r5.0, section 5.2, Link Down event can happen
under any of the following circumstances:

1. Fundamental/Hot reset
2. Link disable transmission by upstream component
3. Moving from L2/L3 to L0

In those cases, Link Down causes some non-sticky DWC registers to loose the
state (like REBAR, etc...). So the drivers need to reinitialize them to
function properly once the link comes back again.

This is not a problem for drivers supporting PERST# IRQ, since they can
reinitialize the registers in the PERST# IRQ callback. But for the drivers
not supporting PERST#, there is no way they can reinitialize the registers
other than relying on Link Down IRQ received when the link goes down. So
let's add a DWC generic API dw_pcie_ep_linkdown() that reinitializes the
non-sticky registers and also notifies the EPF drivers about link going
down.

This API can also be used by the drivers supporting PERST# to handle the
scenario (2) mentioned above.

NOTE: For the sake of code organization, move the dw_pcie_ep_linkup()
definition just above dw_pcie_ep_linkdown().

Reviewed-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
---
 drivers/pci/controller/dwc/pcie-designware-ep.c | 103 ++++++++++++++++--------
 drivers/pci/controller/dwc/pcie-designware.h    |   5 ++
 2 files changed, 73 insertions(+), 35 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
index 78d5fc72c9cb..09ad6f7b5095 100644
--- a/drivers/pci/controller/dwc/pcie-designware-ep.c
+++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
@@ -15,18 +15,6 @@
 #include <linux/pci-epc.h>
 #include <linux/pci-epf.h>
 
-/**
- * dw_pcie_ep_linkup - Notify EPF drivers about Link Up event
- * @ep: DWC EP device
- */
-void dw_pcie_ep_linkup(struct dw_pcie_ep *ep)
-{
-	struct pci_epc *epc = ep->epc;
-
-	pci_epc_linkup(epc);
-}
-EXPORT_SYMBOL_GPL(dw_pcie_ep_linkup);
-
 /**
  * dw_pcie_ep_get_func_from_ep - Get the struct dw_pcie_ep_func corresponding to
  *				 the endpoint function
@@ -661,6 +649,34 @@ static unsigned int dw_pcie_ep_find_ext_capability(struct dw_pcie *pci, int cap)
 	return 0;
 }
 
+static void dw_pcie_ep_init_non_sticky_registers(struct dw_pcie *pci)
+{
+	unsigned int offset;
+	unsigned int nbars;
+	u32 reg, i;
+
+	offset = dw_pcie_ep_find_ext_capability(pci, PCI_EXT_CAP_ID_REBAR);
+
+	dw_pcie_dbi_ro_wr_en(pci);
+
+	if (offset) {
+		reg = dw_pcie_readl_dbi(pci, offset + PCI_REBAR_CTRL);
+		nbars = (reg & PCI_REBAR_CTRL_NBAR_MASK) >>
+			PCI_REBAR_CTRL_NBAR_SHIFT;
+
+		/*
+		 * PCIe r6.0, sec 7.8.6.2 require us to support at least one
+		 * size in the range from 1 MB to 512 GB. Advertise support
+		 * for 1 MB BAR size only.
+		 */
+		for (i = 0; i < nbars; i++, offset += PCI_REBAR_CTRL)
+			dw_pcie_writel_dbi(pci, offset + PCI_REBAR_CAP, 0x0);
+	}
+
+	dw_pcie_setup(pci);
+	dw_pcie_dbi_ro_wr_dis(pci);
+}
+
 /**
  * dw_pcie_ep_init_registers - Initialize DWC EP specific registers
  * @ep: DWC EP device
@@ -675,13 +691,11 @@ int dw_pcie_ep_init_registers(struct dw_pcie_ep *ep)
 	struct dw_pcie_ep_func *ep_func;
 	struct device *dev = pci->dev;
 	struct pci_epc *epc = ep->epc;
-	unsigned int offset, ptm_cap_base;
-	unsigned int nbars;
+	u32 ptm_cap_base, reg;
 	u8 hdr_type;
 	u8 func_no;
-	int i, ret;
 	void *addr;
-	u32 reg;
+	int ret;
 
 	hdr_type = dw_pcie_readb_dbi(pci, PCI_HEADER_TYPE) &
 		   PCI_HEADER_TYPE_MASK;
@@ -744,25 +758,8 @@ int dw_pcie_ep_init_registers(struct dw_pcie_ep *ep)
 	if (ep->ops->init)
 		ep->ops->init(ep);
 
-	offset = dw_pcie_ep_find_ext_capability(pci, PCI_EXT_CAP_ID_REBAR);
 	ptm_cap_base = dw_pcie_ep_find_ext_capability(pci, PCI_EXT_CAP_ID_PTM);
 
-	dw_pcie_dbi_ro_wr_en(pci);
-
-	if (offset) {
-		reg = dw_pcie_readl_dbi(pci, offset + PCI_REBAR_CTRL);
-		nbars = (reg & PCI_REBAR_CTRL_NBAR_MASK) >>
-			PCI_REBAR_CTRL_NBAR_SHIFT;
-
-		/*
-		 * PCIe r6.0, sec 7.8.6.2 require us to support at least one
-		 * size in the range from 1 MB to 512 GB. Advertise support
-		 * for 1 MB BAR size only.
-		 */
-		for (i = 0; i < nbars; i++, offset += PCI_REBAR_CTRL)
-			dw_pcie_writel_dbi(pci, offset + PCI_REBAR_CAP, BIT(4));
-	}
-
 	/*
 	 * PTM responder capability can be disabled only after disabling
 	 * PTM root capability.
@@ -779,8 +776,7 @@ int dw_pcie_ep_init_registers(struct dw_pcie_ep *ep)
 		dw_pcie_dbi_ro_wr_dis(pci);
 	}
 
-	dw_pcie_setup(pci);
-	dw_pcie_dbi_ro_wr_dis(pci);
+	dw_pcie_ep_init_non_sticky_registers(pci);
 
 	return 0;
 
@@ -791,6 +787,43 @@ int dw_pcie_ep_init_registers(struct dw_pcie_ep *ep)
 }
 EXPORT_SYMBOL_GPL(dw_pcie_ep_init_registers);
 
+/**
+ * dw_pcie_ep_linkup - Notify EPF drivers about Link Up event
+ * @ep: DWC EP device
+ */
+void dw_pcie_ep_linkup(struct dw_pcie_ep *ep)
+{
+	struct pci_epc *epc = ep->epc;
+
+	pci_epc_linkup(epc);
+}
+EXPORT_SYMBOL_GPL(dw_pcie_ep_linkup);
+
+/**
+ * dw_pcie_ep_linkdown - Notify EPF drivers about Link Down event
+ * @ep: DWC EP device
+ *
+ * Non-sticky registers are also initialized before sending the notification to
+ * the EPF drivers. This is needed since the registers need to be initialized
+ * before the link comes back again.
+ */
+void dw_pcie_ep_linkdown(struct dw_pcie_ep *ep)
+{
+	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
+	struct pci_epc *epc = ep->epc;
+
+	/*
+	 * Initialize the non-sticky DWC registers as they would've reset post
+	 * Link Down. This is specifically needed for drivers not supporting
+	 * PERST# as they have no way to reinitialize the registers before the
+	 * link comes back again.
+	 */
+	dw_pcie_ep_init_non_sticky_registers(pci);
+
+	pci_epc_linkdown(epc);
+}
+EXPORT_SYMBOL_GPL(dw_pcie_ep_linkdown);
+
 /**
  * dw_pcie_ep_init - Initialize the endpoint device
  * @ep: DWC EP device
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index 49ae845a3662..89f9046af7eb 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -668,6 +668,7 @@ static inline void __iomem *dw_pcie_own_conf_map_bus(struct pci_bus *bus,
 
 #ifdef CONFIG_PCIE_DW_EP
 void dw_pcie_ep_linkup(struct dw_pcie_ep *ep);
+void dw_pcie_ep_linkdown(struct dw_pcie_ep *ep);
 int dw_pcie_ep_init(struct dw_pcie_ep *ep);
 int dw_pcie_ep_init_registers(struct dw_pcie_ep *ep);
 void dw_pcie_ep_deinit(struct dw_pcie_ep *ep);
@@ -687,6 +688,10 @@ static inline void dw_pcie_ep_linkup(struct dw_pcie_ep *ep)
 {
 }
 
+static inline void dw_pcie_ep_linkdown(struct dw_pcie_ep *ep)
+{
+}
+
 static inline int dw_pcie_ep_init(struct dw_pcie_ep *ep)
 {
 	return 0;

-- 
2.25.1