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

[Jean Delvare <jdelvare@suse.de>]

Hi Heiner,

On Sat, 04 Mar 2023 22:33:05 +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.
> 
> 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;

Looks reasonable, I also can't see any reason why that wouldn't work.
But locking and power management can be tricky of course. I'll test
this for some time, but I don't think my system actually suffers from
this ACPI resource conflict, so this most probably won't be testing
much in practice.

Thanks,
-- 
Jean Delvare
SUSE L3 Support