[U-Boot] [PATCH] i2c: mux: Allow muxes to work as children of i2c bus without i2c-parent

[Moritz Fischer]

Hi Michal,

On Tue, Jan 3, 2017 at 1:22 AM, Michal Simek <michal.simek at xilinx.com> wrote:
> On 2.1.2017 20:20, Moritz Fischer wrote:
>> Hi Michal,
>>
>> On Mon, Jan 2, 2017 at 6:24 AM, Michal Simek <michal.simek at xilinx.com> wrote:
>>> On 29.12.2016 23:50, Moritz Fischer wrote:
>>>> For mux check if the parent is already a device of UCLASS_I2C and if yes
>>>> just use that. Otherwise see if someone specified an i2c-parent phandle.
>>>> This mimics the behavior found in the Kernel, as it removes the
>>>> requirement to explicitly specify a i2c-parent phandle.
>>>>
>>>> Signed-off-by: Moritz Fischer <moritz.fischer at ettus.com>
>>>> Cc: Heiko Schocher <hs at denx.de>
>>>> Cc: Bin Meng <bmeng.cn at gmail.com>
>>>> Cc: Simon Glass <sjg at chromium.org>
>>>> Cc: Michal Simek <michal.simek at xilinx.com>
>>>> Cc: u-boot at lists.denx.de
>>>> ---
>>>>  drivers/i2c/muxes/i2c-mux-uclass.c | 9 +++++++++
>>>>  1 file changed, 9 insertions(+)
>>>>
>>>> diff --git a/drivers/i2c/muxes/i2c-mux-uclass.c b/drivers/i2c/muxes/i2c-mux-uclass.c
>>>> index 7a698b6..e01b773 100644
>>>> --- a/drivers/i2c/muxes/i2c-mux-uclass.c
>>>> +++ b/drivers/i2c/muxes/i2c-mux-uclass.c
>>>> @@ -86,6 +86,15 @@ static int i2c_mux_post_probe(struct udevice *mux)
>>>>       debug("%s: %s\n", __func__, mux->name);
>>>>       priv->selected = -1;
>>>>
>>>> +     /* if parent is of i2c uclass already, we'll take that, otherwise
>>>> +      * look if we find an i2c-parent phandle */
>>>
>>> Incorrect comment style.
>>
>> Yeah, wasn't flagged by checkpatch .... will fix.
>>>
>>>> +     if (UCLASS_I2C == device_get_uclass_id(mux->parent)) {
>>>> +             priv->i2c_bus = dev_get_parent(mux);
>>>> +             debug("%s: bus=%p/%s\n", __func__, priv->i2c_bus,
>>>> +                   priv->i2c_bus->name);
>>>> +             return 0;
>>>> +     }
>>>> +
>>>>       ret = uclass_get_device_by_phandle(UCLASS_I2C, mux, "i2c-parent",
>>>>                                          &priv->i2c_bus);
>>>>       if (ret)
>>>>
>>>
>>> The part of this will be good to also handle
>>> req_seq for mux busses. But at least this should solved part of the
>>> problems.
>>
>> I'm not sure I understand this comment.
>
> AFAIK using i2c muxes requires two changes in DTS file.
> First change is this to setup i2c-parent in DTS file which is something
> what Linux doesn't need.

Yeah this part is addressed in this patch.

> The next change is that you have to extend i2c aliases to point to i2c
> mux sub busses which is the second thing what Linux doesn't need.
> I expect that this change you have in your dts file.

Yeah, thanks for clarifying. In my dts I have aliases for each of the
mux channels,
which, I don't have a good idea on how to solve differently. In Linux
I think I don't need that.

> I think that if you detect mux with 8 ports you can simply use unique
> busid to be able to address them.

In Linux? I'll have to take another look at that. Currently I get
busses like 700,701,702 etc (which are aliases I defined).
Each of them points to a mux channel.

<snip>
aliases { ...
                i2c0 = &i2c0;
                i2c0700 = &i2c0_70_0;
                i2c0701 = &i2c0_70_1;
                i2c0702 = &i2c0_70_2;
                i2c0703 = &i2c0_70_3;
};

...
        i2cswitch at 70 {
                compatible = "ti,pca9548", "nxp,pca9548";
                #address-cells = <1>;
                #size-cells = <0>;
                reg = <0x70>;
                status = "okay";

                i2c0_70_0: i2c at 0 {
                        reg = <0x0>;
                        #address-cells = <1>;
                        #size-cells = <0>;

                        status = "okay";
                };
                ...
          };

</snip>

I Will resubmit a v2 for the other changes above

If you or Simon have ideas on how to correctly solve the alias issue,
I can take another stab at that.

Thanks,

Moritz