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SubjectRe: [PATCH 6/7] arm: mediatek: enable gpt6 on boot up to make arch timer working
From
2014-08-11 9:15 GMT+02:00 Linus Walleij <linus.walleij@linaro.org>:
> On Thu, Jul 31, 2014 at 6:42 PM, Matthias Brugger
> <matthias.bgg@gmail.com> wrote:
>
>> We enable GTP6 which ungates the arch timer clock. Apart we write the
>> frequency with which the timer is running in the CNTFREQ register.
>> In the future this should be done in the bootloader.
>>
>> Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>
> (...)
>
>> + if (of_machine_is_compatible("mediatek,mt6589")) {
>> + /* set cntfreq register which is not done in bootloader */
>> + asm volatile("mcr p15, 0, %0, c14, c0, 0" : : "r" (13000000));
>
> I guess this is for something like the ARM arch timer in
> drivers/clocksource/arm_arch_timer.c
>
> Instead of doing this, use the DT property "clock-frequency" on
> the ARM arch timer node, as that overrides the CP15 setting.
>
>> +
>> + /* turn on GPT6 which ungates arch timer clocks */
>> + gpt_base = ioremap(GPT6_CON_MT65xx, 0x04);
>> + }
>> +
>> + /* enabel clock and set to free-run */
>> + if (gpt_base)
>> + writel(0x31, gpt_base);
>
> Why is this not done properly in the GPT driver (I guess
> in drivers/clocksource/mtk_timer.c) instead of remapping
> it and fiddling around in the machine?

I didn't put it in the GPT driver, because that would mean, that you
need to have the mtk_timer to be able to use the ARM arch timer.
From my understanding this are two independent blocks in the SoC.
Apart from that, as stated in the commit message, this patch is a
workaround until we have a bootloader which does this for us.
Therefore I thought the init_time function would be the better place to do this.

Thanks,
Matthias

>
> If it only affects the mt6589 just add another compatible string
> to that driver like "mediatek,mt6589-timer" as it properly reflects the
> fact that this timer is slightly different on the 6589.
>
> Also use a #define for the magic constant 0x31.
>
> Yours,
> Linus Walleij



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