linux-kernel - Re: [PATCH 6/7] arm: mediatek: enable gpt6 on boot up to make arch timer working

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Date:	Tue, 12 Aug 2014 11:02:15 +0200
From:	Matthias Brugger <matthias.bgg@...il.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Mike Turquette <mturquette@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>,
	Jason Cooper <jason@...edaemon.net>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Stephen Warren <swarren@...dia.com>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	stefan@...er.ch, Maxime Ripard <maxime.ripard@...e-electrons.com>,
	"Berg, Anders" <anders.berg@....com>,
	Heiko Stübner <heiko@...ech.de>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 6/7] arm: mediatek: enable gpt6 on boot up to make arch
 timer working

2014-08-11 9:15 GMT+02:00 Linus Walleij <linus.walleij@...aro.org>:
> On Thu, Jul 31, 2014 at 6:42 PM, Matthias Brugger
> <matthias.bgg@...il.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@...il.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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