linux-kernel - Re: [PATCH v2 02/18] clk: intel: Add clock driver for Intel MIPS SoCs

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Date:   Mon, 3 Sep 2018 18:47:39 +0800
From:   "Zhu, Yi Xin" <yixin.zhu@...ux.intel.com>
To:     Stephen Boyd <sboyd@...nel.org>,
        Songjun Wu <songjun.wu@...ux.intel.com>,
        chuanhua.lei@...ux.intel.com, hua.ma@...ux.intel.com,
        qi-ming.wu@...el.com
Cc:     linux-mips@...ux-mips.org, linux-clk@...r.kernel.org,
        linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
        Michael Turquette <mturquette@...libre.com>,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v2 02/18] clk: intel: Add clock driver for Intel MIPS SoCs


On 9/1/2018 1:10 AM, Stephen Boyd wrote:
> Quoting Zhu, Yi Xin (2018-08-28 23:56:22)
>> On 8/28/2018 3:09 AM, Stephen Boyd wrote:
>>> Quoting yixin zhu (2018-08-08 01:52:20)
>>>> On 8/8/2018 1:50 PM, Stephen Boyd wrote:
>>>>>> +/* clock flags definition */
>>>>>> +#define CLOCK_FLAG_VAL_INIT    BIT(16)
>>>>>> +#define GATE_CLK_HW            BIT(17)
>>>>>> +#define GATE_CLK_SW            BIT(18)
>>>>>> +#define GATE_CLK_VT            BIT(19)
>>>>> What does VT mean? Virtual?
>>>> Yes. VT means virtual here.
>>>> Will change to GATE_CLK_VIRT.
>>>>
>>> Is it a hardware concept? Or virtualization with hypervisor?
>> Some peripheral drivers want to use same code cross platforms.
>>
>> But not all platforms provide HW gate clock.  So in this case, clock
>> driver creates
>>
>> a virtual gate clock to make it work if no HW gate clock in the SoC.
> That's not how things are supposed to work. If a clk isn't there in the
> hardware we don't make them up in software so that the consumer software
> drivers can keep requesting clks on different platforms. On a different
> platform, the driver needs to know that the clks aren't there with a
> different compatible string.

OK. Will remove virtual gate clock.


>>
>>>>>> +}
>>>>>> +
>>>>>> +CLK_OF_DECLARE(intel_grx500_cgu, "intel,grx500-cgu", grx500_clk_init);
>>>>> Any reason a platform driver can't be used instead of CLK_OF_DECLARE()?
>>>> It provides CPU clock which is used in early boot stage.
>>>>
>>> Ok. What is the CPU clock doing in early boot stage? Some sort of timer
>>> frequency? If the driver can be split into two pieces, one to handle the
>>> really early stuff that must be in place to get timers up and running
>>> and the other to register the rest of the clks that aren't critical from
>>> a regular platform driver it would be good. That's preferred model if
>>> something is super critical.
>> Yes, CPU clock is providing CPU frequency in the early boot stage.
>>
>> Will put the non-critical clocks in the platform driver.
>>
>>
> Sure the CPU clock is handling frequency, but does that matter for early
> boot to get going? If timers aren't involved here then it doesn't sound
> like this needs CLK_OF_DECLARE.

Yes, timer is involved here.

CPU frequency get by early stage platform code used in clockevent 
registration.


>