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Subject[PATCH v2 3/6] PCI: brcmstb: Add "refusal mode" to preclude PCIe-induced CPU aborts
Date
Our PCIe RC HW has an atypical behavior: if it does not have PCIe link
established between itself and downstream, any subsequent config space
access causes a CPU abort. This commit sets a "refusal mode" if the PCIe
link-up fails, and this has our pci_ops map_bus function returning a NULL
address, which in turn precludes the access from happening.

Right now, "refusal mode" is window dressing. It will become relevant
in a future commit when brcm_pcie_start_link() is invoked during
enumeration instead of before it.

Signed-off-by: Jim Quinlan <jim2101024@gmail.com>
---
drivers/pci/controller/pcie-brcmstb.c | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)

diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
index c026446d5830..72219a4f3964 100644
--- a/drivers/pci/controller/pcie-brcmstb.c
+++ b/drivers/pci/controller/pcie-brcmstb.c
@@ -255,6 +255,7 @@ struct brcm_pcie {
u32 hw_rev;
void (*perst_set)(struct brcm_pcie *pcie, u32 val);
void (*bridge_sw_init_set)(struct brcm_pcie *pcie, u32 val);
+ bool refusal_mode;
};

static inline bool is_bmips(const struct brcm_pcie *pcie)
@@ -687,6 +688,19 @@ static void __iomem *brcm_pcie_map_conf(struct pci_bus *bus, unsigned int devfn,
if (pci_is_root_bus(bus))
return PCI_SLOT(devfn) ? NULL : base + where;

+ if (pcie->refusal_mode) {
+ /*
+ * At this point we do not have PCIe link-up. If there is
+ * a config read or write access besides those targeting
+ * the host bridge, our PCIe HW throws a CPU abort. To
+ * prevent this we return the NULL address. The calling
+ * functions -- pci_generic_config_*() -- will notice this
+ * and not perform the access, and if it is a read access,
+ * 0xffffffff is returned.
+ */
+ return NULL;
+ }
+
/* For devices, write to the config space index register */
idx = PCIE_ECAM_OFFSET(bus->number, devfn, 0);
writel(idx, pcie->base + PCIE_EXT_CFG_INDEX);
@@ -704,6 +718,11 @@ static void __iomem *brcm_pcie_map_conf32(struct pci_bus *bus, unsigned int devf
if (pci_is_root_bus(bus))
return PCI_SLOT(devfn) ? NULL : base + (where & ~0x3);

+ if (pcie->refusal_mode) {
+ /* See note above in brcm_pcie_map_conf() */
+ return NULL;
+ }
+
/* For devices, write to the config space index register */
idx = PCIE_ECAM_OFFSET(bus->number, devfn, (where & ~3));
writel(idx, base + IDX_ADDR(pcie));
@@ -989,6 +1008,7 @@ static int brcm_pcie_start_link(struct brcm_pcie *pcie)
dev_err(dev, "link down\n");
return -ENODEV;
}
+ pcie->refusal_mode = false;

if (!brcm_pcie_rc_mode(pcie)) {
dev_err(dev, "PCIe misconfigured; is in EP mode\n");
@@ -1134,6 +1154,8 @@ static void brcm_pcie_turn_off(struct brcm_pcie *pcie)
void __iomem *base = pcie->base;
int tmp;

+ pcie->refusal_mode = true;
+
if (brcm_pcie_link_up(pcie))
brcm_pcie_enter_l23(pcie);
/* Assert fundamental reset */
@@ -1185,6 +1207,7 @@ static int brcm_pcie_resume(struct device *dev)
u32 tmp;
int ret;

+ pcie->refusal_mode = true;
base = pcie->base;
ret = clk_prepare_enable(pcie->clk);
if (ret)
@@ -1361,6 +1384,7 @@ static int brcm_pcie_probe(struct platform_device *pdev)
pcie->type = data->type;
pcie->perst_set = data->perst_set;
pcie->bridge_sw_init_set = data->bridge_sw_init_set;
+ pcie->refusal_mode = true;

pcie->base = devm_platform_ioremap_resource(pdev, 0);
if (IS_ERR(pcie->base))
--
2.17.1
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