Calling i2c set speed twice for i2c_mux_bus

[Michal Simek]

On 15. 04. 20 8:40, Michal Simek wrote:
> On 10. 04. 20 10:49, Heiko Schocher wrote:
>> Hello Michal,
>>
>> Am 10.04.2020 um 08:46 schrieb Michal Simek:
>>> Hi Heiko,
>>>
>>> On 10. 04. 20 7:11, Heiko Schocher wrote:
>>>> Hello Michal,
>>>>
>>>> Am 09.04.2020 um 16:03 schrieb Michal Simek:
>>>>> Hi Heiko and Simon,
>>>>>
>>>>> I have find out one bug in i2c class. I am using zcu104 revC board
>>>>> which
>>>>> has dts in mainline where i2c1 has i2c mux with some channels.
>>>>> In DT clock-frequency = <400000>; is specified and it is read in
>>>>> i2c_post_probe(). But i2c_mux_bus_drv is also UCLASS_I2C which means
>>>>> that post probe is called for it too. And because clock-frequency
>>>>> property is not there default 100k is used.
>>>>>
>>>>> I think that is bug and should be fixed.
>>>>> Heiko: Are you aware about this issue?
>>>>
>>>> No :-(
>>>>
>>>> The question is, is this a bug?
>>>
>>> I have never seen clock-frequency property in i2c mux bus node. Also I
>>> have looked at linux dt binding docs and nothing like that is specified
>>> there. From quick look also pca954x driver is not reading it.
>>
>> Indeed.
>>
>>>> Should a i2c bus behind a mux not be able to set his own speed?
>>>
>>> Not sure if that make sense but Linux will likely ignore it. I am not
>>> saying it doesn't make sense but I haven't seen this feature.
>>
>> Ok.
>>
>>>> But may as a feature (or bugfix?) if "clock-frequency" is not there,
>>>> use the speed of the parent bus...?
>>>
>>> I was thinking about this too.
>>> just c&p quick implementation would look like this. Because it is
>>> i2c->i2c_mux->i2c. But maybe there is a better way how to do it.
>>>
>>> diff --git a/drivers/i2c/i2c-uclass.c b/drivers/i2c/i2c-uclass.c
>>> index 2aa3efe8aaa0..982c467deba3 100644
>>> --- a/drivers/i2c/i2c-uclass.c
>>> +++ b/drivers/i2c/i2c-uclass.c
>>> @@ -640,9 +640,21 @@ static int i2c_post_probe(struct udevice *dev)
>>>   {
>>>   #if CONFIG_IS_ENABLED(OF_CONTROL) && !CONFIG_IS_ENABLED(OF_PLATDATA)
>>>          struct dm_i2c_bus *i2c = dev_get_uclass_priv(dev);
>>> +       int parent_speed = I2C_SPEED_STANDARD_RATE;
>>> +
>>> +       if (dev->parent &&
>>> +           device_get_uclass_id(dev->parent) == UCLASS_I2C_MUX &&
>>> +           dev->parent->parent &&
>>> +           device_get_uclass_id(dev->parent->parent) == UCLASS_I2C) {
>>> +               struct dm_i2c_bus *i2c_parent;
>>> +
>>> +               i2c_parent = dev_get_uclass_priv(dev->parent->parent);
>>> +               parent_speed = i2c_parent->speed_hz;
>>> +               /* Not sure if make sense to check that parent_speed is
>>> not 0 */
>>
>> I think this check is not needed.
>>
>>> +       }
>>>
>>>          i2c->speed_hz = dev_read_u32_default(dev, "clock-frequency",
>>> -                                            I2C_SPEED_STANDARD_RATE);
>>> +                                            parent_speed);
>>
>> Wow, a big if ... may this is clearer (not compile tested)?
>>
>> udevice *parent = dev_get_parent(dev);
>>
>> if (parent && device_get_uclass_id(parent) == UCLASS_I2C_MUX) {
>>     udevice *parent2 = dev_get_parent(parent);
>>     if (parent2 && device_get_uclass_id(parent2) == UCLASS_I2C) {
>>         struct dm_i2c_bus *i2cp = dev_get_uclass_priv(parent2);
>>
>>         parent_speed = i2cp->speed_hz;
>>     }
>> }
>>
>> but Simon has a deeper DM knowledge, may there is a better approach.
> 
> Simon: any comment on this one?

Simon: Can you please comment this?

Thanks,
Michal