Re: [PATCH 2/4] i2c: i801: Replace acpi_lock with I2C bus lock

[Heiner Kallweit <hkallweit1@gmail.com>]

On 15.06.2023 00:31, Andi Shyti wrote:
> Hi Heiner,
> 
> On Sat, Mar 04, 2023 at 10:33:05PM +0100, Heiner Kallweit wrote:
>> I2C core ensures in i2c_smbus_xfer() that the I2C bus lock is held when
>> calling the smbus_xfer callback. That's i801_access() in our case.
>> I think it's safe in general to assume that the I2C bus lock is held
>> when the smbus_xfer callback is called.
>> Therefore I see no need to define an own mutex.
> 
> I think it makes sense... unless I missed something I don't see
> anything else being racy in i801_access().
> 
> Have you checked i801_acpi_io_handler()?
> 
acpi_os_read_port() resolves to a simple inb() et al.
Therefore I don't see anything in i801_acpi_io_handler()
that would speak against using the I2C bus lock.

> Andi
> 
>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>> ---
>>  drivers/i2c/busses/i2c-i801.c | 14 ++++----------
>>  1 file changed, 4 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
>> index d6a0c3b53..7641bd0ac 100644
>> --- a/drivers/i2c/busses/i2c-i801.c
>> +++ b/drivers/i2c/busses/i2c-i801.c
>> @@ -289,10 +289,9 @@ struct i801_priv {
>>  
>>  	/*
>>  	 * If set to true the host controller registers are reserved for
>> -	 * ACPI AML use. Protected by acpi_lock.
>> +	 * ACPI AML use.
>>  	 */
>>  	bool acpi_reserved;
>> -	struct mutex acpi_lock;
>>  };
>>  
>>  #define FEATURE_SMBUS_PEC	BIT(0)
>> @@ -871,11 +870,8 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
>>  	int hwpec, ret;
>>  	struct i801_priv *priv = i2c_get_adapdata(adap);
>>  
>> -	mutex_lock(&priv->acpi_lock);
>> -	if (priv->acpi_reserved) {
>> -		mutex_unlock(&priv->acpi_lock);
>> +	if (priv->acpi_reserved)
>>  		return -EBUSY;
>> -	}
>>  
>>  	pm_runtime_get_sync(&priv->pci_dev->dev);
>>  
>> @@ -916,7 +912,6 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
>>  
>>  	pm_runtime_mark_last_busy(&priv->pci_dev->dev);
>>  	pm_runtime_put_autosuspend(&priv->pci_dev->dev);
>> -	mutex_unlock(&priv->acpi_lock);
>>  	return ret;
>>  }
>>  
>> @@ -1566,7 +1561,7 @@ i801_acpi_io_handler(u32 function, acpi_physical_address address, u32 bits,
>>  	 * further access from the driver itself. This device is now owned
>>  	 * by the system firmware.
>>  	 */
>> -	mutex_lock(&priv->acpi_lock);
>> +	i2c_lock_bus(&priv->adapter, I2C_LOCK_SEGMENT);
>>  
>>  	if (!priv->acpi_reserved && i801_acpi_is_smbus_ioport(priv, address)) {
>>  		priv->acpi_reserved = true;
>> @@ -1586,7 +1581,7 @@ i801_acpi_io_handler(u32 function, acpi_physical_address address, u32 bits,
>>  	else
>>  		status = acpi_os_write_port(address, (u32)*value, bits);
>>  
>> -	mutex_unlock(&priv->acpi_lock);
>> +	i2c_unlock_bus(&priv->adapter, I2C_LOCK_SEGMENT);
>>  
>>  	return status;
>>  }
>> @@ -1640,7 +1635,6 @@ 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;
>>  	priv->features = id->driver_data;
>> -- 
>> 2.39.2
>>
>>