Date:   Mon, 26 Jun 2017 23:25:19 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Lyude <lyude@...hat.com>
Cc:     intel-gfx@...ts.freedesktop.org,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Benjamin Tissoires <btissoir@...hat.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Jean Delvare <jdelvare@...e.de>,
        Wolfram Sang <wsa@...-dreams.de>,
        Jean Delvare <jdelvare@...e.com>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH] i2c: i801: Allow ACPI SystemIO OpRegion to conflict harder

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@...hat.com>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Benjamin Tissoires <btissoir@...hat.com>
> Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>
> Cc: Jean Delvare <jdelvare@...e.de>
> Cc: Wolfram Sang <wsa@...-dreams.de>
> Cc: intel-gfx@...ts.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@...r.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;
> 

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