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

Heiner Kallweit
2023-06-15T21:22:34Z

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
>>
>>