Subject: [PATCH V4 1/5] phy: Add new Exynos5 USB 3.0 PHY driver

From: [email-masked] (Tomasz Figa)
Date: Mon, 14 Apr 2014 15:49:50 +0200

On 14.04.2014 15:40, Vivek Gautam wrote:
> On Mon, Apr 14, 2014 at 6:56 PM, Kishon Vijay Abraham I <[email-masked]> wrote:
>>
>>
>> On Monday 14 April 2014 06:50 PM, Vivek Gautam wrote:
>>> On Mon, Apr 14, 2014 at 6:29 PM, Kishon Vijay Abraham I <[email-masked]> wrote:
>>>>
>>>>
>>>> On Monday 14 April 2014 06:12 PM, Vivek Gautam wrote:
>>>>> Hi,
>>>>>
>>>>>
>>>>> On Mon, Apr 14, 2014 at 5:57 PM, Kishon Vijay Abraham I <[email-masked]> wrote:
>>>>>> Hi,
>>>>>>
>>>>>> On Tuesday 08 April 2014 08:06 PM, Vivek Gautam wrote:
>>>>>>> Add a new driver for the USB 3.0 PHY on Exynos5 series of SoCs.
>>>>>>> The new driver uses the generic PHY framework and will interact
>>>>>>> with DWC3 controller present on Exynos5 series of SoCs.
>>>>>>> Thereby, removing old phy-samsung-usb3 driver and related code
>>>>>>> used untill now which was based on usb/phy framework.
>>>>>>>
>>>>>>> Signed-off-by: Vivek Gautam <[email-masked]>
>>>>>>> ---
>>>>>>>   .../devicetree/bindings/phy/samsung-phy.txt        |   42 ++
>>>>>>>   drivers/phy/Kconfig                                |   11 +
>>>>>>>   drivers/phy/Makefile                               |    1 +
>>>>>>>   drivers/phy/phy-exynos5-usbdrd.c                   |  668 ++++++++++++++++++++
>>>>>>>   4 files changed, 722 insertions(+)
>>>>>>>   create mode 100644 drivers/phy/phy-exynos5-usbdrd.c
>>>>>>>
>>>>>>> diff --git a/Documentation/devicetree/bindings/phy/samsung-phy.txt b/Documentation/devicetree/bindings/phy/samsung-phy.txt
>>>>>>> index 28f9edb..6d99ba9 100644
>>>>>>> --- a/Documentation/devicetree/bindings/phy/samsung-phy.txt
>>>>>>> +++ b/Documentation/devicetree/bindings/phy/samsung-phy.txt
>>>>>>> @@ -74,3 +74,45 @@ phy-consumer at 12340000 {
>>>>>>>
>>>>>>>   Refer to DT bindings documentation of particular PHY consumer devices for more
>>>>>>>   information about required PHYs and the way of specification.
>>>>>>> +
>>>>>>> +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), associated by
>>>>>>> +            phy name, used to determine bit values for clock settings
>>>>>>> +            register.
>>>>>>> +     Additional clock required for Exynos5420:
>>>>>>> +     - usb30_sclk_100m: Additional special clock used for PHY operation
>>>>>>> +                        depicted as 'sclk_usbphy30' in CMU of Exynos5420.
>>>>>>> +- samsung,syscon-phandle: phandle for syscon interface, which is used to
>>>>>>> +                       control pmu registers for power isolation.
>>>>>>> +- samsung,pmu-offset: phy power control register offset to pmu-system-controller
>>>>>>> +                   base.
>>>>>>> +- #phy-cells : from the generic PHY bindings, must be 1;
>>>>>>> +
>>>>>>> +For "samsung,exynos5250-usbdrd-phy" and "samsung,exynos5420-usbdrd-phy"
>>>>>>> +compatible PHYs, the second cell in the PHY specifier identifies the
>>>>>>> +PHY id, which is interpreted as follows:
>>>>>>> +  0 - UTMI+ type phy,
>>>>>>> +  1 - PIPE3 type phy,
>>>>>>> +
>>>>>>> +Example:
>>>>>>> +     usb3_phy: usbphy at 12100000 {
>>>>>>> +             compatible = "samsung,exynos5250-usbdrd-phy";
>>>>>>> +             reg = <0x12100000 0x100>;
>>>>>>> +             clocks = <&clock 286>, <&clock 1>;
>>>>>>> +             clock-names = "phy", "usb3phy_refclk";
>>>>>>> +             samsung,syscon-phandle = <&pmu_syscon>;
>>>>>>> +             samsung,pmu-offset = <0x704>;
>>>>>>> +             #phy-cells = <1>;
>>>>>>> +     };
>>>>>>> diff --git a/drivers/phy/Kconfig b/drivers/phy/Kconfig
>>>>>>> index 8d3c49c..d955a05 100644
>>>>>>> --- a/drivers/phy/Kconfig
>>>>>>> +++ b/drivers/phy/Kconfig
>>>>>>> @@ -166,4 +166,15 @@ config PHY_XGENE
>>>>>>>        help
>>>>>>>          This option enables support for APM X-Gene SoC multi-purpose PHY.
>>>>>>>
>>>>>>> +config PHY_EXYNOS5_USBDRD
>>>>>>> +     tristate "Exynos5 SoC series USB DRD PHY driver"
>>>>>>> +     depends on ARCH_EXYNOS5 && OF
>>>>>>> +     depends on HAS_IOMEM
>>>>>>> +     select GENERIC_PHY
>>>>>>> +     select MFD_SYSCON
>>>>>>
>>>>>> Lets try to avoid select in Kconfig. We've got enough problems with that.
>>>>>
>>>>> I hope you meant with "select MFD_SYSCON".
>>>>> We are referencing the syscon for accessing pmu reg, for which we need
>>>>> this config to be selected.
>>>>> Other Exynos phy drivers also need this config and for that they have
>>>>> selected this.
>>>>>
>>>>> Do you want me to do it any other way ?
>>>>
>>>> depends on is one option.
>>>
>>> Ok, i can see there are places where depends_on MFD_SYSCON is used.
>>> "drivers/gpu/drm/exynos/Kconfig:60"
>>>
>>> so, do you want me to fix at other places too ?
>>>
>>> But i also have a question here.
>>> MFD_SYSCON is a subsystem that's facilitating us in getting our work
>>> done here by giving an access to pmu_system_controller.
>>> So unless MFD_SYSCON is exposed, the phy driver will not be exposed to us.
>>> So is that valid enough really ?
>>
>> maybe in the Kconfig for MFD_SYSCON, we can select it if PHY_EXYNOS5_USBDRD is
>> enabled?
>>
>> config MFD_SYSCON
>> default y if PHY_EXYNOS5_USBDRD
>
> Yes, that seems to be one option. But we will end up adding this
> dependency for all the drivers which want to use syscon.
>
> Adding few people who worked on MFS_SYSCON, just to gather ideas.
>
> Re-quoting our problem here:
> "Inside our phy driver we are accessing power mgt unit registers,
> which we register using syscon in ut device tree.
> Now we don't want to select MFD_SYSCON from our phy driver, instead
> want to go 'depend_on' way."
>
> So one solution seems to be enabling MFD_SYSCON by default, if any of
> driver using syscon is enabled.
> Can we use some other way here ?

This is an awful idea from maintainability perspective... This means 
that every driver depending on MFD_SYSCON would have to add new "default 
y if" to MFD_SYSCON Kconfig entry. Even with respect to readability, it 
is more logical to have all dependencies of a driver listed in its 
Kconfig entry.

Anyway, PHY_EXYNOS5_USBDRD can't work without MFD_SYSCON and somehow 
this needs to be stated. I believe select is the right thing here and 
I'm not sure why it could be a problem. The biggest reason for going 
this way is that users wouldn't have to care about internal 
dependencies, instead they would simply enable drivers for their hardware.

Best regards,
Tomasz