[PATCH 3/3] i2c: i801: Do not add ICH_RES_IO_SMI if PMC device is not present

[Mika Westerberg]

Martin noticed that nct6775 driver does not load properly on his system
in v5.4+ kernels. The issue was bisected to commit b84398d6d7f9 ("i2c:
i801: Use iTCO version 6 in Cannon Lake PCH and beyond") but it is
likely not the culprit because the faulty code has been in the driver
already since commit 9424693035a5 ("i2c: i801: Create iTCO device on
newer Intel PCHs"). So more likely some commit that added PCI IDs of
recent chipsets made the driver to create the iTCO_wdt device on Martins
system.

The issue was debugged to be PCI configuration access to the PMC device
that is not present. This returns all 1's when read and this caused the
iTCO_wdt driver to accidentally request resourses used by nct6775.

Fix this by checking that the PMC device is there and only then populate
the iTCO_wdt ICH_RES_IO_SMI resource. Since the resource is now optional
the iTCO_wdt driver should continue to work on recent systems without it.

Link: https://lore.kernel.org/linux-hwmon/CAM1AHpQ4196tyD=HhBu-2donSsuogabkfP03v1YF26Q7_BgvgA@xxxxxxxxxxxxxx/
Fixes: 9424693035a5 ("i2c: i801: Create iTCO device on newer Intel PCHs")
Reported-by: Martin Volf <martin.volf.42@xxxxxxxxx>
Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
---
 drivers/i2c/busses/i2c-i801.c | 45 +++++++++++++++++++++--------------
 1 file changed, 27 insertions(+), 18 deletions(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index ca4f096fef74..7fa58375bd4b 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -1519,7 +1519,7 @@ static DEFINE_SPINLOCK(p2sb_spinlock);
 
 static struct platform_device *
 i801_add_tco_spt(struct i801_priv *priv, struct pci_dev *pci_dev,
-		 struct resource *tco_res)
+		 struct resource *tco_res, size_t nres)
 {
 	struct resource *res;
 	unsigned int devfn;
@@ -1563,7 +1563,7 @@ i801_add_tco_spt(struct i801_priv *priv, struct pci_dev *pci_dev,
 	res->flags = IORESOURCE_MEM;
 
 	return platform_device_register_resndata(&pci_dev->dev, "iTCO_wdt", -1,
-					tco_res, 3, &spt_tco_platform_data,
+					tco_res, nres + 1, &spt_tco_platform_data,
 					sizeof(spt_tco_platform_data));
 }
 
@@ -1574,19 +1574,20 @@ static const struct itco_wdt_platform_data cnl_tco_platform_data = {
 
 static struct platform_device *
 i801_add_tco_cnl(struct i801_priv *priv, struct pci_dev *pci_dev,
-		 struct resource *tco_res)
+		 struct resource *tco_res, size_t nres)
 {
 	return platform_device_register_resndata(&pci_dev->dev, "iTCO_wdt", -1,
-					tco_res, 2, &cnl_tco_platform_data,
+					tco_res, nres, &cnl_tco_platform_data,
 					sizeof(cnl_tco_platform_data));
 }
 
 static void i801_add_tco(struct i801_priv *priv)
 {
 	u32 base_addr, tco_base, tco_ctl, ctrl_val;
-	struct pci_dev *pci_dev = priv->pci_dev;
+	struct pci_dev *pmc_dev, *pci_dev = priv->pci_dev;
 	struct resource tco_res[3], *res;
 	unsigned int devfn;
+	size_t nres = 0;
 
 	/* If we have ACPI based watchdog use that instead */
 	if (acpi_has_watchdog())
@@ -1606,29 +1607,37 @@ static void i801_add_tco(struct i801_priv *priv)
 	res->start = tco_base & ~1;
 	res->end = res->start + 32 - 1;
 	res->flags = IORESOURCE_IO;
+	nres++;
 
 	/*
 	 * Power Management registers.
 	 */
 	devfn = PCI_DEVFN(PCI_SLOT(pci_dev->devfn), 2);
-	pci_bus_read_config_dword(pci_dev->bus, devfn, ACPIBASE, &base_addr);
+	pmc_dev = pci_get_slot(pci_dev->bus, devfn);
+	if (pmc_dev) {
+		pci_read_config_dword(pmc_dev, ACPIBASE, &base_addr);
 
-	res = &tco_res[ICH_RES_IO_SMI];
-	res->start = (base_addr & ~1) + ACPIBASE_SMI_OFF;
-	res->end = res->start + 3;
-	res->flags = IORESOURCE_IO;
+		res = &tco_res[ICH_RES_IO_SMI];
+		res->start = (base_addr & ~1) + ACPIBASE_SMI_OFF;
+		res->end = res->start + 3;
+		res->flags = IORESOURCE_IO;
+		nres++;
 
-	/*
-	 * Enable the ACPI I/O space.
-	 */
-	pci_bus_read_config_dword(pci_dev->bus, devfn, ACPICTRL, &ctrl_val);
-	ctrl_val |= ACPICTRL_EN;
-	pci_bus_write_config_dword(pci_dev->bus, devfn, ACPICTRL, ctrl_val);
+		/*
+		 * Enable the ACPI I/O space.
+		 */
+		pci_read_config_dword(pmc_dev, ACPICTRL, &ctrl_val);
+		ctrl_val |= ACPICTRL_EN;
+		pci_write_config_dword(pmc_dev, ACPICTRL, ctrl_val);
+
+		pci_dev_put(pmc_dev);
+	}
 
 	if (priv->features & FEATURE_TCO_CNL)
-		priv->tco_pdev = i801_add_tco_cnl(priv, pci_dev, tco_res);
+		priv->tco_pdev = i801_add_tco_cnl(priv, pci_dev, tco_res, nres);
 	else
-		priv->tco_pdev = i801_add_tco_spt(priv, pci_dev, tco_res);
+		priv->tco_pdev = i801_add_tco_spt(priv, pci_dev, tco_res, nres);
+
 
 	if (IS_ERR(priv->tco_pdev))
 		dev_warn(&pci_dev->dev, "failed to create iTCO device\n");
-- 
2.25.0