Calling i2c set speed twice for i2c_mux_bus

[Simon Glass]

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.

Regards,
Simon