Calling i2c set speed twice for i2c_mux_bus

Thu May 7 10:18:47 CEST 2020

On 06. 05. 20 16:47, Simon Glass wrote:
> Hi Michal,
> 
> On Tue, 5 May 2020 at 21:43, Simon Glass <sjg at chromium.org> wrote:
>>
>> Hi Michal,
>>
>> On Tue, 5 May 2020 at 02:26, Michal Simek <michal.simek at xilinx.com> wrote:
>>>
>>> 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?
>>>
>>
>> OK will take a look.
> 
> I wonder if i2c-mux-uclass.c should define a new uclass for muxed I2C
> buses, something like UCLASS_I2C_MUXED_BUS? Then you can define the
> behaviour correctly in i2c-mux-uclass.c.
> 
> An I2C controller is not the same as a muxed bus and perhaps we should
> be explicitly about the differences. It probably just needs changes to
> the mux uclass.

Definitely there need to be some changes in connection to i2c muxes. I
am aware also about bad behavior when you detect devices.
Just look at log below and you will see that devices on base i2c bus are
copied also to subbus (especially listing i2c-mux again looks weird).

Thanks,
Michal

ZynqMP> i2c bus
Bus 0:	i2c at ff030000  (active 0)
   20: gpio at 20, offset len 1, flags 0
   74: i2c-mux at 74, offset len 1, flags 0
Bus 1:	i2c at ff030000->i2c-mux at 74->i2c at 0  (active 1)
   54: eeprom at 54, offset len 1, flags 0
Bus 2:	i2c at ff030000->i2c-mux at 74->i2c at 1
Bus 3:	i2c at ff030000->i2c-mux at 74->i2c at 2
Bus 4:	i2c at ff030000->i2c-mux at 74->i2c at 3
Bus 5:	i2c at ff030000->i2c-mux at 74->i2c at 5
Bus 6:	i2c at ff030000->i2c-mux at 74->i2c at 7
ZynqMP> i2c dev 1
Setting bus to 1
ZynqMP> i2c probe
Valid chip addresses: 20 54 55 56 57 74
ZynqMP> i2c bus
Bus 0:	i2c at ff030000  (active 0)
   20: gpio at 20, offset len 1, flags 0
   74: i2c-mux at 74, offset len 1, flags 0
Bus 1:	i2c at ff030000->i2c-mux at 74->i2c at 0  (active 1)
   54: eeprom at 54, offset len 1, flags 0
   20: generic_20, offset len 1, flags 0
   74: generic_74, offset len 1, flags 0
Bus 2:	i2c at ff030000->i2c-mux at 74->i2c at 1
Bus 3:	i2c at ff030000->i2c-mux at 74->i2c at 2
Bus 4:	i2c at ff030000->i2c-mux at 74->i2c at 3
Bus 5:	i2c at ff030000->i2c-mux at 74->i2c at 5
Bus 6:	i2c at ff030000->i2c-mux at 74->i2c at 7
ZynqMP> i2c dev 2
Setting bus to 2
ZynqMP> i2c probe
Valid chip addresses: 20 6C 74
ZynqMP> i2c bus
Bus 0:	i2c at ff030000  (active 0)
   20: gpio at 20, offset len 1, flags 0
   74: i2c-mux at 74, offset len 1, flags 0
Bus 1:	i2c at ff030000->i2c-mux at 74->i2c at 0  (active 1)
   54: eeprom at 54, offset len 1, flags 0
   20: generic_20, offset len 1, flags 0
   74: generic_74, offset len 1, flags 0
Bus 2:	i2c at ff030000->i2c-mux at 74->i2c at 1  (active 2)
   20: generic_20, offset len 1, flags 0
   6c: generic_6c, offset len 1, flags 0
   74: generic_74, offset len 1, flags 0
Bus 3:	i2c at ff030000->i2c-mux at 74->i2c at 2
Bus 4:	i2c at ff030000->i2c-mux at 74->i2c at 3
Bus 5:	i2c at ff030000->i2c-mux at 74->i2c at 5
Bus 6:	i2c at ff030000->i2c-mux at 74->i2c at 7