[PATCH] ARM: fix regression in RealView after the introduction of pclk

[Linus Walleij]

2010/7/30 Russell King - ARM Linux <linux at arm.linux.org.uk>:
> On Fri, Jul 30, 2010 at 05:27:28PM +0200, Linus Walleij wrote:
>> In the PB1176 manual there is a drawing of the clock tree, it
>> shows that the fixed 24MHz reference clock is divided by a binary
>> divider down to 1 MHz. So this one is likewise set in stone. I would
>> be surprised if some other scheme was used for the other boards.
>
> That's not quite the full story, because there's this in the code:
>
>        /*
>         * set clock frequency:
>         *      REALVIEW_REFCLK is 32KHz
>         *      REALVIEW_TIMCLK is 1MHz
>         */
>        val = readl(__io_address(REALVIEW_SCTL_BASE));
>        writel((REALVIEW_TIMCLK << REALVIEW_TIMER1_EnSel) |
>               (REALVIEW_TIMCLK << REALVIEW_TIMER2_EnSel) |
>               (REALVIEW_TIMCLK << REALVIEW_TIMER3_EnSel) |
>               (REALVIEW_TIMCLK << REALVIEW_TIMER4_EnSel) | val,
>               __io_address(REALVIEW_SCTL_BASE));
>
> which isn't documented in the user manual.  Yet it's necessary in order
> to run the timers at 1MHz.

Yeah that thing is fun, it looks like a plain mux. Setting the bits
to zero muxes in the 32768 Hz clock and setting one muxes in
the clock from the 24 Mhz / 24 divider. (Easy enough to verify,
I'll test it some day when I'm bored.)

>> Thinking about it I however see that since some platforms are
>> initializing their clocks in .init_irq and some in core_initcall(), some
>> in arch_initcall() etc, and since most platforms have some clock
>> implementation these dats, it might be worth it to add an
>> optional .init_clocks() call to the struct machine_desc and
>> MACHINE_START() macro to get this in uniform and call
>> that even before .init_irq(). Do you think it's worth it?
>
> It may be, but it's rather a large change to do.  We can certainly
> provide the .init_clocks callback so new stuff can use it.

Yeah I meant it to be voluntary stuff, I'll see what I can do.

Yours,
Linus Walleij