[PATCH] i2c: i801: Allow ACPI SystemIO OpRegion to conflict harder

[Lyude]

There's quite a number of machines on the market, mainly Lenovo
ThinkPads, that make the horrible mistake in their firmware of reusing
the PCIBAR space reserved for the SMBus for things that are completely
unrelated to the SMBus controller, such as the OpRegion used for i915.
This is very bad and entirely evil, but with Lenovo's historically poor
track record of fixing their firmware, it is extremely unlikely this is
ever going to be properly fixed.

So, while it would be nice if we could just cut off the SMBus controller
and call it a day this unfortunately breaks RMI4 mode completely for
most of the ThinkPads. Even though this behavior is extremely wrong, for
whatever reason sharing the PCIBAR between the OpRegion and SMBus seems
to be just fine. Regardless however, I think it's safe to assume that
when the BIOS accesses the PCIBAR space of the SMBus controller like
this that it's trying to get to something else that we mapped the SMBus
controller over.

On my X1 Carbon, this assumption appears to be correct. I've traced down
the firmware accesses to being caused by the firmware mistakenly placing
the SWSCI mailbox for i915 on top of the SMBus host controller region.
And indeed, blacklisting i915 causes the firmware to never attempt to
touch this region.

So, in order to try to workaround this and not break either SMBus or
i915, we temporarily unmap the PCI device for the SMBus controller,
do the thing that the firmware wanted to do, then remap the device and
report a firmware bug.

Signed-off-by: Lyude <lyude@xxxxxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Benjamin Tissoires <btissoir@xxxxxxxxxx>
Cc: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
Cc: Jean Delvare <jdelvare@xxxxxxx>
Cc: Wolfram Sang <wsa@xxxxxxxxxxxxx>
Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
---
So: unfortunately

a7ae81952cda (i2c: i801: Allow ACPI SystemIO OpRegion to conflict with PCI BAR)

Seems to prevent the ThinkPad X1 Carbon 4th gen and the T460s from actually
using their SMBus controllers at all. As mentioned above, I've traced the issue
down to the firmware responding to the SWSCI by sticking data in places it
shouldn't, e.g. the SMBus registers.

I'm entirely unsure if this patch is the correct fix for this, and wouldn't be
at all surprised if it's just as bad of a patch as I think it is ;P. So I
figured I'd send it to intel-gfx and the authors of the original version of this
patch to get their take on it and see if there might be something less hacky we
can do to fix this.

 drivers/i2c/busses/i2c-i801.c | 41 +++++++++++++++++++++++++----------------
 1 file changed, 25 insertions(+), 16 deletions(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index 6484fa6..bfbe0f9 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -1406,33 +1406,42 @@ i801_acpi_io_handler(u32 function, acpi_physical_address address, u32 bits,
 {
 	struct i801_priv *priv = handler_context;
 	struct pci_dev *pdev = priv->pci_dev;
+	struct device *dev = &pdev->dev;
 	acpi_status status;
+	int err;
 
-	/*
-	 * Once BIOS AML code touches the OpRegion we warn and inhibit any
-	 * further access from the driver itself. This device is now owned
-	 * by the system firmware.
-	 */
 	mutex_lock(&priv->acpi_lock);
 
-	if (!priv->acpi_reserved) {
-		priv->acpi_reserved = true;
+	/*
+	 * BIOS AML code should never actually touch the SMBus registers,
+	 * however crappy firmware (mainly Lenovo's) can make the mistake of
+	 * mapping things over the SMBus region that should definitely not be
+	 * there (such as the OpRegion for Intel GPUs).
+	 * This is extremely bad firmware behavior, but it is unlikely this will
+	 * ever get fixed by Lenovo.
+	 */
+	dev_warn_once(dev,
+		      FW_BUG "OpRegion overlaps with SMBus registers, working around\n");
 
-		dev_warn(&pdev->dev, "BIOS is accessing SMBus registers\n");
-		dev_warn(&pdev->dev, "Driver SMBus register access inhibited\n");
-
-		/*
-		 * BIOS is accessing the host controller so prevent it from
-		 * suspending automatically from now on.
-		 */
-		pm_runtime_get_sync(&pdev->dev);
-	}
+	pm_runtime_get_sync(dev);
+	pcim_iounmap_regions(pdev, 1 << SMBBAR);
 
 	if ((function & ACPI_IO_MASK) == ACPI_READ)
 		status = acpi_os_read_port(address, (u32 *)value, bits);
 	else
 		status = acpi_os_write_port(address, (u32)*value, bits);
 
+	err = pcim_iomap_regions(pdev, 1 << SMBBAR,
+				 dev_driver_string(&pdev->dev));
+	if (err) {
+		dev_err(&pdev->dev,
+			FW_BUG "Failed to restore SMBus region 0x%lx-0x%Lx. SMBus is now broken.\n",
+			priv->smba,
+			(unsigned long long)pci_resource_end(pdev, SMBBAR));
+		priv->acpi_reserved = true;
+	}
+
+	pm_runtime_put(dev);
 	mutex_unlock(&priv->acpi_lock);
 
 	return status;
-- 
2.9.4