Re: [PATCH v3] i2c: i801: Allow ACPI SystemIO OpRegion to conflict with PCI BAR

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Wed, May 11, 2016 at 11:39:33AM +0200, Jean Delvare wrote:
> Hi Mika,
> 
> First of all, thank you very much for working on this problem, this is
> highly appreciated.

You're welcome :)

> On Mon,  9 May 2016 11:17:14 +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-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 v2:
> > 
> >  - Return -EIO instead of -EPERM
> >  - Added ACK from Rafael
> >  - Added Link and Reported-by tags
> >  - Tagged for stable inclusion
> > 
> >  drivers/i2c/busses/i2c-i801.c | 106 ++++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 102 insertions(+), 4 deletions(-)
> 
> I have tested this on my Dell OptiPlex 9020 MT system, and it works
> well. Gives me access to the SPD EEPROMs on my memory modules.

Good to know. Thanks for testing.

> Below is my review.
> 
> > diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
> > index 5652bf6ce9be..d69ad96460b5 100644
> > --- a/drivers/i2c/busses/i2c-i801.c
> > +++ b/drivers/i2c/busses/i2c-i801.c
> > @@ -247,6 +247,13 @@ struct i801_priv {
> >  	struct platform_device *mux_pdev;
> >  #endif
> >  	struct platform_device *tco_pdev;
> > +
> > +	/*
> > +	 * If set to true the host controller registers are reserved for
> > +	 * ACPI AML use. Protected by acpi_lock.
> > +	 */
> > +	bool acpi_reserved;
> > +	struct mutex acpi_lock;
> >  };
> >  
> >  #define FEATURE_SMBUS_PEC	(1 << 0)
> > @@ -720,6 +727,12 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
> >  	int ret = 0, xact = 0;
> >  	struct i801_priv *priv = i2c_get_adapdata(adap);
> >  
> > +	mutex_lock(&priv->acpi_lock);
> > +	if (priv->acpi_reserved) {
> > +		mutex_unlock(&priv->acpi_lock);
> > +		return -EIO;
> 
> I see this has been discussed before, but I don't think EIO is
> appropriate here. You didn't even try to issue an I/O to the device, so
> how could it fail? EBUSY would better reflect the situation IMHO.

That works for me as well. Rafael suggested -EIO and it was originally
-EPERM but I have no problems changing it to return -EBUSY.

> > +	}
> > +
> >  	pm_runtime_get_sync(&priv->pci_dev->dev);
> >  
> >  	hwpec = (priv->features & FEATURE_SMBUS_PEC) && (flags & I2C_CLIENT_PEC)
> > @@ -822,6 +835,7 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
> >  out:
> >  	pm_runtime_mark_last_busy(&priv->pci_dev->dev);
> >  	pm_runtime_put_autosuspend(&priv->pci_dev->dev);
> > +	mutex_unlock(&priv->acpi_lock);
> >  	return ret;
> >  }
> >  
> > @@ -1260,6 +1274,89 @@ static void i801_add_tco(struct i801_priv *priv)
> >  	priv->tco_pdev = pdev;
> >  }
> >  
> > +#ifdef CONFIG_ACPI
> > +static acpi_status
> > +i801_acpi_io_handler(u32 function, acpi_physical_address address, u32 bits,
> > +		     u64 *value, void *handler_context, void *region_context)
> > +{
> > +	struct i801_priv *priv = handler_context;
> > +	struct pci_dev *pdev = priv->pci_dev;
> > +	acpi_status status;
> > +
> > +	/*
> > +	 * 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.
> > +	 */
> > +	dev_warn_once(&pdev->dev, "BIOS is accessing SMBus registers\n");
> > +	dev_warn_once(&pdev->dev, "Driver SMBus register access inhibited\n");
> 
> Given that you have priv->acpi_reserved to record if we've been there
> before, maybe you could move the warnings below, and use simple
> dev_warn? I suspect it's cheaper than dev_warn_once.

OK, I'll move them to the block below.

> > +
> > +	mutex_lock(&priv->acpi_lock);
> > +
> > +	if (!priv->acpi_reserved) {
> > +		priv->acpi_reserved = true;
> > +
> > +		/*
> > +		 * BIOS is accessing the host controller so prevent it from
> > +		 * suspending automatically from now on.
> > +		 */
> > +		pm_runtime_get_sync(&pdev->dev);
> > +	}
> > +
> > +	if (function == ACPI_READ) {
> > +		u32 val = (u32)*value;
> 
> I'm confused. acpi_os_read_port is writing the result of the read to
> "val", it doesn't read from it, so I don't think it needs to be
> initialized?

Indeed, that's not needed at all.

> Also, looking at the acpi_os_read_port() call in
> drivers/acpi/apei/apei-base.c, it would seem you can cast *value
> directly in-place, without using a temporary variable. This would limit
> the overhead.

OK.

> > +		status = acpi_os_read_port(address, &val, bits);
> > +		if (ACPI_SUCCESS(status))
> > +			*value = val;
> > +	} else {
> > +		status = acpi_os_write_port(address, (u32)*value, bits);
> > +	}
> > +
> > +	mutex_unlock(&priv->acpi_lock);
> > +
> > +	return status;
> > +}
> > +
> > +static int i801_acpi_probe(struct i801_priv *priv)
> > +{
> > +	struct acpi_device *adev;
> > +	acpi_status status;
> > +
> > +	adev = ACPI_COMPANION(&priv->pci_dev->dev);
> > +	if (adev) {
> > +		status = acpi_install_address_space_handler(adev->handle,
> > +				ACPI_ADR_SPACE_SYSTEM_IO, i801_acpi_io_handler,
> > +				NULL, priv);
> > +		if (ACPI_SUCCESS(status))
> > +			return 0;
> > +	}
> > +
> > +	return acpi_check_resource_conflict(&priv->pci_dev->resource[SMBBAR]);
> > +}
> > +
> > +static void i801_acpi_remove(struct i801_priv *priv)
> > +{
> > +	struct acpi_device *adev;
> > +
> > +	adev = ACPI_COMPANION(&priv->pci_dev->dev);
> > +	if (!adev)
> > +		return;
> > +
> > +	acpi_remove_address_space_handler(adev->handle,
> > +		ACPI_ADR_SPACE_SYSTEM_IO, i801_acpi_io_handler);
> > +
> > +	mutex_lock(&priv->acpi_lock);
> > +	if (priv->acpi_reserved) {
> > +		priv->acpi_reserved = false;
> 
> Is this actually needed? priv is about to be destroyed anyway.

It is not needed. I'll remove it.

> > +		pm_runtime_put(&priv->pci_dev->dev);
> > +	}
> > +	mutex_unlock(&priv->acpi_lock);
> > +}
> > +#else
> > +static inline int i801_acpi_probe(struct i801_priv *priv) { return 0; }
> > +static inline void i801_acpi_remove(struct i801_priv *priv) { }
> > +#endif
> > +
> >  static int i801_probe(struct pci_dev *dev, const struct pci_device_id *id)
> >  {
> >  	unsigned char temp;
> > @@ -1277,6 +1374,7 @@ static int i801_probe(struct pci_dev *dev, const struct pci_device_id *id)
> >  	priv->adapter.dev.parent = &dev->dev;
> >  	ACPI_COMPANION_SET(&priv->adapter.dev, ACPI_COMPANION(&dev->dev));
> >  	priv->adapter.retries = 3;
> > +	mutex_init(&priv->acpi_lock);
> >  
> >  	priv->pci_dev = dev;
> >  	switch (dev->device) {
> > @@ -1339,10 +1437,9 @@ static int i801_probe(struct pci_dev *dev, const struct pci_device_id *id)
> >  		return -ENODEV;
> >  	}
> >  
> > -	err = acpi_check_resource_conflict(&dev->resource[SMBBAR]);
> > -	if (err) {
> > -		return -ENODEV;
> > -	}
> > +	err = i801_acpi_probe(priv);
> > +	if (err)
> > +		return err;
> 
> Before your patch we would return -ENODEV in case of conflict. Now we
> are returning -EBUSY instead. I see no reason for this change. Or if
> you think this is actually needed, that seems independent from what
> your patch is doing, so it should be a separate patch.

Returning -ENODEV seems to be right thing to do. I'll change it in the
next version.

> >  
> >  	err = pcim_iomap_regions(dev, 1 << SMBBAR,
> >  				 dev_driver_string(&dev->dev));
> > @@ -1439,6 +1536,7 @@ static void i801_remove(struct pci_dev *dev)
> >  	pm_runtime_forbid(&dev->dev);
> >  	pm_runtime_get_noresume(&dev->dev);
> >  
> > +	i801_acpi_remove(priv);
> >  	i801_del_mux(priv);
> >  	i2c_del_adapter(&priv->adapter);
> 
> This looks racy. Until i2c_del_adapter() is called, the SMBus may be
> used. So I think you should call i801_acpi_remove() after
> i2c_del_adapter().

That's right. I'll move the call to happen after i2c_del_adapter() is
called.

Thanks for the review.
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