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Date:   Mon, 24 Feb 2020 13:27:40 +0200
From:   Mika Westerberg <mika.westerberg@linux.intel.com>
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc:     Guenter Roeck <linux@roeck-us.net>,
        Martin Volf <martin.volf.42@gmail.com>,
        Jean Delvare <jdelvare@suse.com>,
        Wolfram Sang <wsa@the-dreams.de>, linux-i2c@vger.kernel.org,
        linux-hwmon@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jarkko Nikula <jarkko.nikula@linux.intel.com>
Subject: Re: [regression] nct6775 does not load in 5.4 and 5.5, bisected to
 b84398d6d7f90080
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On Mon, Feb 24, 2020 at 12:51:25PM +0200, Mika Westerberg wrote:
> > I'm wondering if
> > 
> > 		pci_dev_is_present(...);
> > 
> > returns false here.
> 
> Well that might also be the case since lspci shows this:
> 
> 00:1f.0 ISA bridge: Intel Corporation Z390 Chipset LPC/eSPI Controller (rev 10)
> 00:1f.3 Audio device: Intel Corporation Cannon Lake PCH cAVS (rev 10)
> 00:1f.4 SMBus: Intel Corporation Cannon Lake PCH SMBus Controller (rev 10)
> 
> PMC is 1f.2 and not present here. However, it may be that the PMC is
> still there it just does not "enumerate" because its devid/vendorid are
> set to 0xffff. Similar hiding was done for the P2SB bridge.

Actually I think this is the case here.

I don't know the iTCO_wdt well enough to say if it could live without
the ICH_RES_IO_SMI. It looks like this register is used to disable SMI
generation but not sure how well it works if it is left to BIOS to
configure. I suppose these systems should use WDAT instead.

Martin, can you try the below patch?

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index ba87305f4332..c16e5ad08641 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -1593,7 +1593,7 @@ i801_add_tco_cnl(struct i801_priv *priv, struct pci_dev *pci_dev,
 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;
 
@@ -1620,7 +1620,12 @@ static void i801_add_tco(struct i801_priv *priv)
 	 * 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) {
+		dev_info(&pci_dev->dev, "PMC device disabled, not enabling iTCO\n");
+		return;
+	}
+	pci_read_config_dword(pmc_dev, ACPIBASE, &base_addr);
 
 	res = &tco_res[ICH_RES_IO_SMI];
 	res->start = (base_addr & ~1) + ACPIBASE_SMI_OFF;
@@ -1630,15 +1635,17 @@ static void i801_add_tco(struct i801_priv *priv)
 	/*
 	 * Enable the ACPI I/O space.
 	 */
-	pci_bus_read_config_dword(pci_dev->bus, devfn, ACPICTRL, &ctrl_val);
+	pci_read_config_dword(pmc_dev, ACPICTRL, &ctrl_val);
 	ctrl_val |= ACPICTRL_EN;
-	pci_bus_write_config_dword(pci_dev->bus, devfn, ACPICTRL, ctrl_val);
+	pci_write_config_dword(pmc_dev, ACPICTRL, ctrl_val);
 
 	if (priv->features & FEATURE_TCO_CNL)
 		priv->tco_pdev = i801_add_tco_cnl(priv, pci_dev, tco_res);
 	else
 		priv->tco_pdev = i801_add_tco_spt(priv, pci_dev, tco_res);
 
+	pci_dev_put(pmc_dev);
+
 	if (IS_ERR(priv->tco_pdev))
 		dev_warn(&pci_dev->dev, "failed to create iTCO device\n");
 }