[PATCH v3 7/9] PCI: dwc: ep: Add a generic dw_pcie_ep_linkdown() API to handle Link Down event

Manivannan Sadhasivam
2024-04-18T11:59:19Z

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 2063cf2049e5..b878b62460f3 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_init_notify - Notify EPF drivers about EPC initialization complete
* @ep: DWC EP device
@@ -673,6 +661,34 @@ 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
@@ -687,13 +703,11 @@ 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;
@@ -756,25 +770,8 @@ 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.
@@ -791,8 +788,7 @@ 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;

@@ -803,6 +799,43 @@ 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 f8e5431a207b..152969545b0a 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_init_notify(struct dw_pcie_ep *ep);
@@ -688,6 +689,10 @@ 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