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

[Zhu, Yi Xin]

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.


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