[PATCH 1/2] timer: mtk_timer: initialize the timer before use

[Weijie Gao]

On Fri, 2021-01-15 at 17:36 +0100, Matthias Brugger wrote:
> On Tue, Jan 12, 2021 at 01:44:02PM +0800, Weijie Gao wrote:
> > The timer being used by this driver may have already been used by first
> > stage bootloader (e.g. ATF/preloader), and it's settings may differ from
> > what this driver is going to use.
> > 
> > This may cause issues, such as inaccurate timer frequency due to
> > incorrect clock divider.
> > 
> > This patch adds the initialization code to avoid them.
> > 
> > Signed-off-by: Weijie Gao <weijie.gao at mediatek.com>
> > ---
> >  drivers/timer/mtk_timer.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/drivers/timer/mtk_timer.c b/drivers/timer/mtk_timer.c
> > index 448a76a7e1..f6b97f868c 100644
> > --- a/drivers/timer/mtk_timer.c
> > +++ b/drivers/timer/mtk_timer.c
> > @@ -61,6 +61,16 @@ static int mtk_timer_probe(struct udevice *dev)
> >  	if (!uc_priv->clock_rate)
> >  		return -EINVAL;
> >  
> > +	/*
> > +	 * Initialize the timer:
> > +	 * 1. set clock source to system clock with clock divider setting to 1
> > +	 * 2. set timer mode to free running
> > +	 * 3. reset timer counter to 0 then enable the timer
> > +	 */
> > +	writel(GPT4_CLK_SYS | GPT4_CLK_DIV1, priv->base + MTK_GPT4_CLK);
> > +	writel(GPT4_FREERUN | GPT4_CLEAR | GPT4_ENABLE,
> 
> GPT4_FREERUN is defined as GENMASK(5,4) while in the Linux kernel it has
> the value of 3. Can you explain where this difference comes from?

GENMASK(5,4) == 3 << 4, which is exactly the same as what's being used
in kernel:

#define GPT_CTRL_OP(val)        (((val) & 0x3) << 4)
#define GPT_CTRL_OP_FREERUN     (3)

> 
> Regards,
> Matthias
> 
> > +	       priv->base + MTK_GPT4_CTRL);
> > +
> >  	return 0;
> >  }
> >  
> > -- 
> > 2.17.1