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

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Message-ID: <1432130725.20394.24.camel@mtksdaap41>
Date:	Wed, 20 May 2015 22:05:25 +0800
From:	Yingjoe Chen <yingjoe.chen@...iatek.com>
To:	Matthias Brugger <matthias.bgg@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stephen Boyd <sboyd@...eaurora.org>
CC:	Mark Rutland <mark.rutland@....com>,
	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, 2015-05-20 at 13:02 +0200, Matthias Brugger 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.
> ---- 8< ---------------- >8 ------
> From 631e7bf4e5d9456d0bb4a29b2dee4b84e8c052bd Mon Sep 17 00:00:00 2001
> From: Matthias Brugger <matthias.bgg@...il.com>
> Date: Wed, 20 May 2015 12:43:16 +0200
> Subject: [PATCH] clocksource: mediatek: Define mtk_clock_event_device globally
> 
> Sched clock code, especially sched_clock_register does not allow to pass a
> pointer to actual_read_sched_clock. So if in the driver the register base
> address is not globally defined, we are not able to read the scheduler
> clock register. This patch sets the mtk_clock_event_device struct globally
> for the driver, to be able to read the register.

Hi,

I'm not sure using a global device pointer is any better.

Actually, almost every user of sched_clock_register need to keep a
global register base address. Does it make sense to fix this in
sched_clock_register?


> Signed-off-by: Matthias Brugger <matthias.bgg@...il.com>
> ---
>  drivers/clocksource/mtk_timer.c | 50 +++++++++++++++--------------------------
>  1 file changed, 18 insertions(+), 32 deletions(-)
> 
> diff --git a/drivers/clocksource/mtk_timer.c b/drivers/clocksource/mtk_timer.c
> index 68ab423..c5f5b40 100644
> --- a/drivers/clocksource/mtk_timer.c
> +++ b/drivers/clocksource/mtk_timer.c
> @@ -59,13 +59,9 @@ struct mtk_clock_event_device {
>      struct clock_event_device dev;
>  };
> 
> -static inline struct mtk_clock_event_device *to_mtk_clk(
> -                struct clock_event_device *c)
> -{
> -    return container_of(c, struct mtk_clock_event_device, dev);
> -}
> +struct mtk_clock_event_device *evt;

The name is too short even if we make it static:

static struct mtk_clock_event_device *evt __read_mostly;

Joe.C


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