Re: [PATCH] cpufreq: imx: Add cpufreq driver for imx7D/Solo SOC

[Bai Ping]

On 2015/11/24 17:08, Lucas Stach wrote:
> Am Dienstag, den 24.11.2015, 15:35 +0800 schrieb Bai Ping:
> > On 2015/11/23 17:40, Lucas Stach wrote:
> > > Am Montag, den 23.11.2015, 22:07 +0800 schrieb Bai Ping:
> > > > The i.MX7Dual/Solo is a new series of the i.MX SOC family.
> > > > The existing cpufreq driver for 'i.MX6' or 'cpufreq-dt' can
> > > > NOT match the requirement of this new SOC. This patch adds the
> > > > cpufreq driver for i.MX7Dual/Solo.
> > > So, what are those requirements, which could not be matched with
> > > cpufreq-dt? We should really try to not add another cpufreq driver.
> > the requirement is the PLL1 used to source the CPU core clock can NOT
> > change frequency on the fly,
> > during the PLL1 frequency change, not clock output from this PLL1 in a
> > short time. this will lead to glitch
> > to the core clock. so before we change the PLL1's frequency, we must
> > switch the CPU core clock to another
> > clock source,  after the PLL1 frequency has been changed, we switch back
> > core clock to PLL1.
> > > I don't see anything special in here. A single regulator and some clocks
> > > needing to be controlled in the right way. That's already handled for
> > > i.MX5 with cpufreq-dt. Please look up how it is done there and try to do
> > > it the same way for MX7, or provide substantial information why it
> > > couldn't be done.
> > I have checked the i.MX5 cpufreq, As on i.MX5, no need to take care of
> > the PLL's frequency change flow,
> > so the cpufreq-dt is the best one to support cpufreq. But on i.MX7, the
> > PLL design is not the same as on i.MX5,
> > additional steps needed in CPU frequency changing flow. the issue that
> > can NOT be tackled by cpufreq-dt is
> > additional step used by PLL frequency change.
> This is wrong, we have the step clock requirement on MX5 as well, that's
> why I asked you to look into this. The MX5 clock controller provides a
> virtual ARM clock, that implements the proper clock switch flow. This
> allows to reuse cpufreq-dt, thus reducing code duplication in the
> cpufreq drivers greatly.
Thanks for your reminder. It is my fault, I missed the imx_clk_cpu 
function. I will try using cpufreq-dt
on i.MX7 just like i.MX5.

BR
Jacky Bai
> Regards,
> Lucas

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