Re: [PATCH v2 02/16] arm64: dts: add sp804 timer node for Hi6220

On Mon, Apr 4, 2016 at 3:42 PM, Leo Yan [off-list ref] wrote:

On Mon, Apr 04, 2016 at 01:21:00PM +0200, Linus Walleij wrote:

quoted

This is not about enabling/disabling the clock(s) to the timer.
It doesn't matter if these clocks are always on.

It is about determining the *frequency* of the timers.

It is vital that the timer driver get the right frequency of the clock
to the block from the clock implementation, and I do not think
it is the same as the "apb_pclk".

Thanks for reminding. Fortunately, apb_pclk and timer's clock are
same, all of them's rate are 19.2MHz.

OK I was wrong, worrying about nothing.

quoted

The thing is that of course "any frequency" will
work but what you will notice is that the timer runs very
weirdly compared to wall-clock time unless the right clock
yielding the right frequency has been specified here.

Compared sp804 timer counter with wall-clock (which is using ARM's
arch timer), and confirmed that sp804 timer's counter register is
decreasing with rate 19.2MHz.

Thanks, awesome.

Also have checked Hi6220's spec, there have no timer's dediated clock
enabling bits. This is the reason before I only registered one clock.
So according to you and Rob's comments, how about change as below?

                dual_timer0: timer@f8008000 {
                        compatible = "arm,sp804", "arm,primecell";
                        reg = <0x0 0xf8008000 0x0 0x1000>;
                        interrupts = <GIC_SPI 14 IRQ_TYPE_LEVEL_HIGH>,
                                     <GIC_SPI 15 IRQ_TYPE_LEVEL_HIGH>;
                        clocks = <&ao_ctrl HI6220_TIMER0_PCLK>,
                                 <&ao_ctrl HI6220_TIMER0_PCLK>,
                                 <&ao_ctrl HI6220_TIMER0_PCLK>;
                        clock-names = "apb_pclk", "apb_pclk", "apb_pclk";

This works for me, though I think only the last name
matters so I would name the first two "timer1" and "timer2".

Yours,
Linus Walleij