linux-kernel - Re: [PATCH v2 4/9] clocksource: mediatek: Use GPT as sched clock source

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Date:	Fri, 3 Jul 2015 21:48:42 +0800
From:	Daniel Kurtz <djkurtz@...omium.org>
To:	Matthias Brugger <matthias.bgg@...il.com>
Cc:	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Mark Rutland <mark.rutland@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Pawel Moll <pawel.moll@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Marc Carino <marc.ceeeee@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	linux-mediatek@...ts.infradead.org,
	Sascha Hauer <kernel@...gutronix.de>,
	srv_heupstream <srv_heupstream@...iatek.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 4/9] clocksource: mediatek: Use GPT as sched clock source

On Wed, May 20, 2015 at 7:02 PM, Matthias Brugger
<matthias.bgg@...il.com> wrote:
> 2015-05-16 9:58 GMT+02:00 Yingjoe Chen <yingjoe.chen@...iatek.com>:
>> When cpu is in deep idle, arch timer will stop counting. Setup GPT as
>> sched clock source so it can keep counting in idle.
>>
>> Signed-off-by: Yingjoe Chen <yingjoe.chen@...iatek.com>
>> ---
>>  drivers/clocksource/mtk_timer.c | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/drivers/clocksource/mtk_timer.c b/drivers/clocksource/mtk_timer.c
>> index 91206f9..fe7cf72 100644
>> --- a/drivers/clocksource/mtk_timer.c
>> +++ b/drivers/clocksource/mtk_timer.c
>> @@ -24,6 +24,7 @@
>>  #include <linux/of.h>
>>  #include <linux/of_address.h>
>>  #include <linux/of_irq.h>
>> +#include <linux/sched_clock.h>
>>  #include <linux/slab.h>
>>
>>  #define GPT_IRQ_EN_REG         0x00
>> @@ -59,6 +60,13 @@ struct mtk_clock_event_device {
>>         struct clock_event_device dev;
>>  };
>>
>> +static void __iomem *gpt_base __read_mostly;
>> +
>> +static u64 notrace mtk_read_sched_clock(void)
>> +{
>> +       return readl_relaxed(gpt_base + TIMER_CNT_REG(GPT_CLK_SRC));
>> +}
>> +
>>  static inline struct mtk_clock_event_device *to_mtk_clk(
>>                                 struct clock_event_device *c)
>>  {
>> @@ -243,6 +251,8 @@ static void __init mtk_timer_init(struct device_node *node)
>>         mtk_timer_setup(evt, GPT_CLK_SRC, TIMER_CTRL_OP_FREERUN, 1);
>>         clocksource_mmio_init(evt->gpt_base + TIMER_CNT_REG(GPT_CLK_SRC),
>>                         node->name, rate, 300, 32, clocksource_mmio_readl_up);
>> +       gpt_base = evt->gpt_base;
>
> This is really hacky. We should clean up the code and provide
> mtk_clock_event_device globally.
> Please add the patch below, which does exactly this.

I don't think this is so hacky.
In light of Stephen's comment about the benefit of using
container_of() to extract gpt_base from the passed in struct
clock_event_device in the other routines, what is the benefit of
making more of mtk_clock_event_device global?
I think what Yingjoe has implemented is short and sweet.

Reviewed-by: Daniel Kurtz <djkurtz@...omium.org>
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