| Message ID | 20170626204009.32607-1-lyude@redhat.com |
|---|---|
| State | Needs Review / ACK |
| Headers | show |
On Monday, June 26, 2017 04:40:08 PM Lyude wrote: > 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@redhat.com> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > Cc: Benjamin Tissoires <btissoir@redhat.com> > Cc: Mika Westerberg <mika.westerberg@linux.intel.com> > Cc: Jean Delvare <jdelvare@suse.de> > Cc: Wolfram Sang <wsa@the-dreams.de> > Cc: intel-gfx@lists.freedesktop.org > --- > 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. It would really help to send this to linux-acpi@vger.kernel.org (as pretty much everything ACPI-related). Adding the CC and retaining the patch below for completeness. > > 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; >
On Mon, Jun 26, 2017 at 04:40:08PM -0400, Lyude wrote: > 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. Are the registers it tries to access separate from SMBus ones? We already have TCO registers placed to this device starting from Skylake so there might be something else as well. Point here is that if the access is not to the SMBus registers we can quirk it in the driver and let the access happen because it does not mess our state.
On Mon, Jun 26, 2017 at 04:40:08PM -0400, Lyude wrote: > 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@redhat.com> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > Cc: Benjamin Tissoires <btissoir@redhat.com> > Cc: Mika Westerberg <mika.westerberg@linux.intel.com> > Cc: Jean Delvare <jdelvare@suse.de> > Cc: Wolfram Sang <wsa@the-dreams.de> > Cc: intel-gfx@lists.freedesktop.org > --- > 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. How does "that other" operating system handle this? FWIW I own a ThinkPad X1 Carbon 4th Gen, so I'm happy for your work on it :) Kind regards, David
On Mon, Jun 26, 2017 at 04:40:08PM -0400, Lyude wrote: > 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@redhat.com> No full name? Or is it your full name? > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > Cc: Benjamin Tissoires <btissoir@redhat.com> > Cc: Mika Westerberg <mika.westerberg@linux.intel.com> > Cc: Jean Delvare <jdelvare@suse.de> > Cc: Wolfram Sang <wsa@the-dreams.de> > Cc: intel-gfx@lists.freedesktop.org I don't know this matter at all. I'd need comments from these people on CC to proceed with this one. > --- > 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 >
On Sat, 2017-08-12 at 13:15 +0200, Wolfram Sang wrote: > On Mon, Jun 26, 2017 at 04:40:08PM -0400, Lyude wrote: > > 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@redhat.com> > > No full name? Or is it your full name? Looks like I forgot to change my desktop's S-B identity to full name, but it shouldn't be a big deal. I've got tons of other patches already upstream like this. > > > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > Cc: Benjamin Tissoires <btissoir@redhat.com> > > Cc: Mika Westerberg <mika.westerberg@linux.intel.com> > > Cc: Jean Delvare <jdelvare@suse.de> > > Cc: Wolfram Sang <wsa@the-dreams.de> > > Cc: intel-gfx@lists.freedesktop.org > > I don't know this matter at all. I'd need comments from these people > on > CC to proceed with this one. > > > --- > > 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 > >
> > > Signed-off-by: Lyude <lyude@redhat.com> > > > > No full name? Or is it your full name? > Looks like I forgot to change my desktop's S-B identity to full name, > but it shouldn't be a big deal. I've got tons of other patches already > upstream like this. I'd much prefer a full name. But more importantly, what I definately need is some review/ack/whatever because I don't know enough about this stuff (other than knowing it is a fragile area). Maybe you could resend with full name and the acpi list on CC? Regards, Wolfram
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;
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@redhat.com> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Cc: Benjamin Tissoires <btissoir@redhat.com> Cc: Mika Westerberg <mika.westerberg@linux.intel.com> Cc: Jean Delvare <jdelvare@suse.de> Cc: Wolfram Sang <wsa@the-dreams.de> Cc: intel-gfx@lists.freedesktop.org --- 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(-)