ARM: Zynq: CPUFreq issues in setting frequencies (Was: Re: Help about PetaLinux)

[Sören Brinkmann]

On Sat, 2014-04-12 at 02:14PM +0530, Viresh Kumar wrote:
> On Sat, Apr 12, 2014 at 3:02 AM, Mokhtar Bouain
> <mokhtar.bouain at gmail.com> wrote:
> > Hi Viresh,
> > Please, I have a problem with the PetaLinux and Zynq board.
> > I posted my probem here :
> > http://forums.xilinx.com/t5/Embedded-Linux/clk-set-rate-failed-to-set-i2c0-aper-rate-zc702-board-and/td-p/438352
> > There is a member of the xilinx forum who you mentioned that you found the
> > solution.
> > Can you help me please?
> 
> Hi Mokhtar,
> 
> I don't have a clue what's going on here as I haven't been looking
> at platform internals at all..
> 
> Soren/Michal are probably working on those things, they might help.
> 

All the information is actually in the forum and referenced topics
there...
Unfortunately, Zynq has plenty inter dependencies between clocks.
That results in all kinds of limitations, because Zynq's timers are
driven by their bus clock which is derived from the CPU clock.
And also other peripherals are clocked by this clock. So, a solution
needs to take all these dependencies into account, which means that
certain operations may fail.

Also, the issue described affects (an outdated version of) our vendor
tree only. We just merged cpufreq support into mainline. We'll see
how that goes.

	Sören