Calling i2c set speed twice for i2c_mux_bus

[Michal Simek]

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?

Thanks,
Michal