[RFC] Reset pins of phys and their representation in a device tree

[Javier Martinez Canillas]

Hello ChenYu

On Thu, May 12, 2016 at 9:49 AM, Chen-Yu Tsai <wens at csie.org> wrote:
> Hi,
>
> On Thu, May 12, 2016 at 9:40 PM, Javier Martinez Canillas
> <javier at dowhile0.org> wrote:
>> [adding Krzysztof as cc]
>>
>> On Thu, May 12, 2016 at 8:25 AM, Sergei Shtylyov
>> <sergei.shtylyov at cogentembedded.com> wrote:
>>> Hello.
>>>
>>>
>>> On 5/12/2016 10:15 AM, Uwe Kleine-König wrote:
>>>
>>>> I have a machine here where the reset pin of the phy is connected to a
>>>> GPIO.
>>>>
>>>> There are different possibilities available today to handle this
>>>> situation, here are the ones I'm aware of:
>>>>
>>>>  - Use a gpio-hog to set the reset gpio to non-active
>>>>    This might result in dependency problems (and that's what I am
>>>>    currently faced with) because there is no connection in the device
>>>>    tree between the hog and the phy.
>>>>
>>>>  - [Documentation/devicetree/bindings/net/fsl-fec.txt]
>>>>    The fec node supports properties
>>>>
>>>>         phy-reset-gpios = <&gpio2 14 0>;
>>>>         phy-reset-duration = <200> /* milliseconds */;
>>>>
>>>>    Something similar exists in TI's vendor kernel
>>>>
>>>> (http://git.ti.com/ti-linux-kernel/ti-linux-kernel/commit/17d192b999ee904ced223c16cef76111a51c461b)
>>>>    with different (and IMHO bader) naming.
>>>>    This is the wrong place to specify the gpios; they shouldn't be in the
>>>>    mac's node, but in a phy node instead.
>>>>
>>>> So what I actually want is to put the gpio specification in the right
>>>> place and let it look as follows:
>>>>
>>>>         mymdiobus {
>>>>                 [...]
>>>>                 myfirstphy: ethernet-phy at 0 {
>>>>                         compatible = "ethernet-phy-ieee802.3-c22";
>>>>                         reg = <0>;
>>>>
>>>>                         reset-gpios = <&gpio2 14 0>;
>>>>                         reset-duration-ms = <200>;
>>>>                 };
>>>>
>>>>                 mysecondphy: ethernet-phy at 2 {
>>>>                         compatible = "ethernet-phy-ieee802.3-c22";
>>>>                         reg = <2>;
>>>>
>>>>                         reset-gpios = <&gpio3 10 0>;
>>>>                         reset-duration-ms = <200>;
>>>>                 };
>>>>         };
>>>>
>>>> And with this we could defer probe of &myfirstphy if &gpio2 isn't
>>>> available yet.
>>>>
>>>> Does this sound sensible? Does something like that already exist which I
>>>> missed? Any further ideas/comments?
>>>
>>>
>>> http://patchwork.ozlabs.org/patch/616495/
>>>
>>>    I'll post a new version RSN.
>>>
>>
>> This seems to be similar to what's needed by MMC/SD/SDIO devices (i.e:
>> a WiFi chip) that needs some power sequence for reset and be
>> enumerable.
>>
>> Krzysztof has been working  to make the MMC pwrseq framework more
>> generic [0] since he wants to use it also for built-in USB devices.
>>
>> From a quick look at the patches mentioned in this thread, it seems
>> that the same framework can be used to reset the PHYs unless I'm
>> missing something. Have you considered using this? It would be good if
>> there is a consistent way to define the power sequence for devices
>> across the different subsystems.
>>
>> [0]: https://lkml.org/lkml/2016/5/5/230
>
> You probably missed the part that Rob nacked the bindings in that
> series?
>

No, I didn't miss that. AFAICT the way forward is still being
discussed as you can see from the last email in that thread from Ulf
[0].

And yes, the DT bindings is likely to change (keeping the backward
compat for MMC) which is good,  but still the power sequence
management code can be reused across subsystems.

> Putting the reset gpios under the PHY nodes and handling it from
> phylib is probably the way to go. I'd like to ask for regulator
> and clock support as well, if possible.
>

A GPIO array, clock and regulator (after Krzysztof patch) is already
supported by the pwrseq_simple provider for example.

> Regards
> ChenYu

[0]: https://lkml.org/lkml/2016/5/10/320