Re: [PATCH v7 1/2] phy: Add new Exynos5 USB 3.0 PHY driver

[Vivek Gautam]

On Fri, May 9, 2014 at 4:21 PM, Vivek Gautam <gautam.vivek@xxxxxxxxxxx> wrote:
> Hi Sylwester,
>
>
> On Fri, May 9, 2014 at 3:43 PM, Sylwester Nawrocki
> <s.nawrocki@xxxxxxxxxxx> wrote:
>> Hi Vivek,
>>
>> On 08/05/14 11:03, Vivek Gautam wrote:
>>>>>> diff --git a/Documentation/devicetree/bindings/phy/samsung-phy.txt b/Documentation/devicetree/bindings/phy/samsung-phy.txt
>>>>>> >>> index b422e38..51efe4c 100644
>>>>>> >>> --- a/Documentation/devicetree/bindings/phy/samsung-phy.txt
>>>>>> >>> +++ b/Documentation/devicetree/bindings/phy/samsung-phy.txt
>>>>>> >>> @@ -114,3 +114,43 @@ Example:
>>>>>> >>>               compatible = "samsung,exynos-sataphy-i2c";
>>>>>> >>>               reg = <0x38>;
>>>>>> >>>       };
>>>>>> >>> +
>>>>>> >>> +Samsung Exynos5 SoC series USB DRD PHY controller
>>>>>> >>> +--------------------------------------------------
>>>>>> >>> +
>>>>>> >>> +Required properties:
>>>>>> >>> +- compatible : Should be set to one of the following supported values:
>>>>>> >>> +     - "samsung,exynos5250-usbdrd-phy" - for exynos5250 SoC,
>>>>>> >>> +     - "samsung,exynos5420-usbdrd-phy" - for exynos5420 SoC.
>>>>>> >>> +- reg : Register offset and length of USB DRD PHY register set;
>>>>>> >>> +- clocks: Clock IDs array as required by the controller
>>>>>> >>> +- clock-names: names of clocks correseponding to IDs in the clock property;
>>>>>> >>> +            Required clocks:
>>>>>> >>> +     - phy: main PHY clock (same as USB DRD controller i.e. DWC3 IP clock),
>>>>>> >>> +            used for register access.
>>>>>> >>> +     - ref: PHY's reference clock (usually crystal clock), used for
>>>>>> >>> +            PHY operations, associated by phy name. It is used to
>>>>>> >>> +            determine bit values for clock settings register.
>>>>>> >>> +            For Exynos5420 this is given as 'sclk_usbphy30' in CMU.
>>>>>> >>> +- samsung,pmu-syscon: phandle for PMU system controller interface, used to
>>>>>> >>> +                   control pmu registers for power isolation.
>>>>>> >>> +- samsung,pmu-offset: phy power control register offset to pmu-system-controller
>>>>>> >>> +                   base.
>>>>> >>
>>>>> >> It doesn't seem right to have register offset encoded in the device tree
>>>>> >> like this. I think it'd be more appropriate to associate such an offset
>>>>> >> with the compatible string's value in the driver.
>>>> >
>>>> > Ok, it makes more sense.
>>>> > Just out of curiosity, what difference would this make ?
>>>
>>> Moreover, in case of Exynos5420 (and may be in future SoCs), where we
>>> have 2 USB DRD PHY controllers,
>>> we will need to have a way around to deal with two separate offsets in
>>> the driver for one compatible string.
>>
>> It could be handled by creating a list of offsets per compatible string and
>> then adding some way to identify the PHY device instance. So I believe that's
>> not a big issue.
>
> True, we had tried to make use of 'aliases' for multiple controllers
> on Exynos5420,
> in earlier version V3 of this patch, to handle the pmu-register
> offsets in _somewhat_ similar fashion. [1]
> But then we had to drop that as per the suggestions in the mailing list.
>
>> Now you'd be encoding a list of registers offsets in the
>> device tree, without encoding bit layout of each register. It's unlikely that
>> each instance would have different bits layout, but describing individual
>> registers in DT I thought is something that we're not supposed to do.
>
> Ok, so this is information to me, i was not very much aware of this.
> Thanks for explaining it here.
>
>>
>>> Getting the offsets from DT seems a cleaner way to handle this case of
>>> multi controllers.
>>
>> I think it's easier from the driver POV, but isn't it violating the device
>> tree rules ?
>> Anyway. I'm just pointing this minor issue in the binding as it appears
>> to me. The final word of course belongs to a DT binding maintainer.
>
> Thanks Sylwester, for pointing this out here.
> Meantime, please let me know if the approach using aliases is one
> possible solution for this or not ?

I shall be sending v8 patch series for this, in order to use 'aliases'
in the driver
to get the distinction between pmu-offsets.
So, v8 will give an alternative approach for getting pmu-offsets using
macro definitions from a header file.

Mark and Rob can suggest us which can be a better approach.

>
>
> [1] [PATCH v3] phy: Add new Exynos5 USB 3.0 PHY driver
>      https://lkml.org/lkml/2014/1/21/46



-- 
Best Regards
Vivek Gautam
Samsung R&D Institute, Bangalore
India
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