Re: [PATCH v4] i2c: i801: Allow ACPI SystemIO OpRegion to conflict with PCI BAR

[Jean Delvare <jdelvare@suse.de>]

Hi Mika,

On Fri, 13 May 2016 15:45:55 +0300, Mika Westerberg wrote:
> Many Intel systems the BIOS declares a SystemIO OpRegion below the SMBus
> PCI device as can be seen in ACPI DSDT table from Lenovo Yoga 900:
> 
>   Device (SBUS)
>   {
>       OperationRegion (SMBI, SystemIO, (SBAR << 0x05), 0x10)
>       Field (SMBI, ByteAcc, NoLock, Preserve)
>       {
>           HSTS,   8,
>           Offset (0x02),
>           HCON,   8,
>           HCOM,   8,
>           TXSA,   8,
>           DAT0,   8,
>           DAT1,   8,
>           HBDR,   8,
>           PECR,   8,
>           RXSA,   8,
>           SDAT,   16
>       }
> 
> There are also bunch of AML methods that that the BIOS can use to access
> these fields. Most of the systems in question AML methods accessing the
> SMBI OpRegion are never used.
> 
> Now, because of this SMBI OpRegion many systems fail to load the SMBus
> driver with an error looking like one below:
> 
>   ACPI Warning: SystemIO range 0x0000000000003040-0x000000000000305F
>        conflicts with OpRegion 0x0000000000003040-0x000000000000304F
>        (\_SB.PCI0.SBUS.SMBI) (20160108/utaddress-255)
>   ACPI: If an ACPI driver is available for this device, you should use
>        it instead of the native driver
> 
> The reason is that this SMBI OpRegion conflicts with the PCI BAR used by
> the SMBus driver.
> 
> It turns out that we can install a custom SystemIO address space handler
> for the SMBus device to intercept all accesses through that OpRegion. This
> allows us to share the PCI BAR with the AML code if it for some reason is
> using it. We do not expect that this OpRegion handler will ever be called
> but if it is we print a warning and prevent all access from the SMBus
> driver itself.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=110041
> Reported-by: Andy Lutomirski <luto@kernel.org>
> Reported-and-tested-by: Pali Rohár <pali.rohar@gmail.com>
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Cc: stable@vger.kernel.org
> ---
> Changes to v3:
>  
>  - Added Tested-by from Pali Rohár (The patch did not change that much so I
>    though it is still valid)
>  - Return -EBUSY instead of -EIO
>  - Move dev_warns() to be inside if (!priv->acpi_reserved) block
>  - Remove unnecessary variable "val"
>  - Do not clear priv->acpi_reserved in i801_acpi_remove()
>  - Return -ENODEV if we detect conflict
>  - Call i801_acpi_remove() after i2c_del_adapter().
> (...)

Tested-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Jean Delvare <jdelvare@suse.de>

Thanks,
-- 
Jean Delvare
SUSE L3 Support