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Subject: Re: [PATCH v9 01/22] dt-bindings: ARM: Mediatek: Add new document
 bindings of imp i2c wrapper controller
To:     Chen-Yu Tsai <wenst@chromium.org>, Stephen Boyd <sboyd@kernel.org>
Cc:     Chun-Jie Chen <chun-jie.chen@mediatek.com>,
        Rob Herring <robh@kernel.org>,
        Nicolas Boichat <drinkcat@chromium.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mediatek@lists.infradead.org, linux-clk@vger.kernel.org,
        devicetree@vger.kernel.org, srv_heupstream@mediatek.com,
        Project_Global_Chrome_Upstream_Group@mediatek.com,
        Weiyi Lu <weiyi.lu@mediatek.com>
References: <20210524122053.17155-1-chun-jie.chen@mediatek.com>
 <20210524122053.17155-2-chun-jie.chen@mediatek.com>
 <20210602171201.GA3566462@robh.at.kernel.org>
 <66e017401ab93aa02c5d2bbf11be9589b36649ac.camel@mediatek.com>
 <1f59ed31-4a0e-9719-bf84-1fe4cdd6c57d@gmail.com>
 <162334689784.9598.2709970788186333494@swboyd.mtv.corp.google.com>
 <de082c64-ace3-30b5-7404-1f4b607a83e1@gmail.com>
 <c8e8535cef67adeaefcfe943bbd8287806921e03.camel@mediatek.com>
 <CAGXv+5HcV6jbyDdZGzRX-2NHMztSONBKxmLxLQX6k+aQrwJ1ww@mail.gmail.com>
From:   Matthias Brugger <matthias.bgg@gmail.com>
Message-ID: <5c0a88c7-7f64-fd00-4e0c-2b3163926f71@gmail.com>
Date:   Fri, 18 Jun 2021 15:50:52 +0200
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On 18/06/2021 08:32, Chen-Yu Tsai wrote:
> On Wed, Jun 16, 2021 at 2:34 AM Chun-Jie Chen
> <chun-jie.chen@mediatek.com> wrote:
>>
>> On Fri, 2021-06-11 at 11:56 +0200, Matthias Brugger wrote:
>>>
>>> On 10/06/2021 19:41, Stephen Boyd wrote:
>>>> Quoting Matthias Brugger (2021-06-08 07:45:49)
>>>>>
>>>>>
>>>>> On 07/06/2021 07:20, Chun-Jie Chen wrote:
>>>>>> On Wed, 2021-06-02 at 12:12 -0500, Rob Herring wrote:
>>>>>>>> +
>>>>>>>> +description:
>>>>>>>> +  The Mediatek imp i2c wrapper controller provides
>>>>>>>> functional
>>>>>>>> configurations and clocks to the system.
>>>>>>>> +
>>>>>>>> +properties:
>>>>>>>> +  compatible:
>>>>>>>> +    items:
>>>>>>>> +      - enum:
>>>>>>>> +          - mediatek,mt8192-imp_iic_wrap_c
>>>>>>>> +          - mediatek,mt8192-imp_iic_wrap_e
>>>>>>>> +          - mediatek,mt8192-imp_iic_wrap_s
>>>>>>>> +          - mediatek,mt8192-imp_iic_wrap_ws
>>>>>>>> +          - mediatek,mt8192-imp_iic_wrap_w
>>>>>>>> +          - mediatek,mt8192-imp_iic_wrap_n
>>>>>>>
>>>>>>> Looks to me like these are all the same h/w, but just have
>>>>>>> differing
>>>>>>> sets of clocks. That's not really a reason to have different
>>>>>>> compatibles.
>>>>>>>
>>>>>>> If you need to know what clocks are present, you can walk the
>>>>>>> DT for
>>>>>>> all 'clocks' properties matching this clock controller
>>>>>>> instance. Or
>>>>>>> use
>>>>>>> 'clock-indices' to define which ones are present.
>>>>
>>>> Is the idea to use clock-indices and then list all the clock ids in
>>>> there and match them up at driver probe time to register the clocks
>>>> provided by the IO region? Feels like we'll do a lot of parsing at
>>>> each
>>>> boot to match up structures and register clks with the clk
>>>> framework.
>>>>
>>>> If it's like other SoCs then the clk id maps to a hard macro for a
>>>> type
>>>> of clk, and those hard macros have been glued together with other
>>>> clks
>>>> and then partitioned into different IO regions to make up a clock
>>>> controller. Or maybe in this case, those clk hard macros have been
>>>> scattered into each IP block like SPI, i2c, uart, etc. so that the
>>>> clock
>>>> controller doesn't really exist and merely the gates and rate
>>>> control
>>>> (mux/divider) for the clk that's clocking some particular IP block
>>>> all
>>>> live inside the IP wrapper. If it's this case then I hope there are
>>>> a
>>>> bunch of PLLs that are fixed rate so that the i2c clk doesn't have
>>>> to go
>>>> outside the wrapper to change frequency (of which there should be
>>>> two
>>>> "standard" frequencies anyway).
>>>>
>>>>>>>
>>>>>>> Rob
>>>>>>
>>>>>> Some module is divided to sub-modules which are designed in
>>>>>> different
>>>>>> h/w blocks for different usage, and if we want to use the same
>>>>>> compatible to present these h/w blocks, we need to move the
>>>>>> clock data
>>>>>> provided by these h/w blocks to dts, but we usually use
>>>>>> different
>>>>>> compatible to get the h/w blocks data in
>>>>>> Mediatek's clock driver, so do you suggest to register clock
>>>>>> provided
>>>>>> by different h/w blocks using same compatible?
>>>>>>
>>>>>
>>>>> The mapping of them is as following:
>>>>> imp_iic_wrap_c:  11007000
>>>>> imp_iic_wrap_e:  11cb1000
>>>>> imp_iic_wrap_s:  11d03000
>>>>> imp_iic_wrap_ws: 11d23000
>>>>> imp_iic_wrap_w:  11e01000
>>>>> imp_iic_wrap_n:  11f02000
>>>>>
>>>>
>>>> Sure. What is their purpose though? Are they simply a bunch of
>>>> different
>>>> i2c clks?
>>>>
>>>
>>> That would be need to be answered by MediaTek as I don't have access
>>> to any
>>> documentation.
>>>
>>> Regards,
>>> Matthias
>>
>> We describe which clock controllers are exist in dts and
>> get the clock data provided by clock controller in driver data
>> by matching device compatible.
>>
>> The clock data contains several clocks which includes the clock index,
>> parent clock source and the details of reg control inside the IP block
>> of clock controller.
>>
>> In MT8192 platform, some IP block is divide to several sub-blocks and
>> each sub-block provides clock control by itself.
> 
> Some more information:
> 
> Based on what I read in the datasheets, I'm guessing that MediaTek groups
> the I2C controllers into several groups and places them in different parts
> of the die. The suffix of imp_iic_wrap_XXX is likely pointing to the
> placement of the group. And the imp_iic_wrap_XXX is what the name suggests
> a wrapper around the group of I2C controllers. The wrapper contains clock
> and reset controls, as well as other things that I can't make out.
> 

Thanks for the clarification. If the wrapper contains more then just clocks,
then probably we will need a solution as done by MMSYS subsystem. Would be good
if you could work with MediaTek to find out what exactly this wrappers contain,
to get a better picture of if we need an additional driver or not.

Regards,
Matthias