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

[Matthias Brugger <matthias.bgg@kernel.org>]

On Mon, Jan 18, 2021 at 08:44:42AM +0800, Weijie Gao wrote:
> 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@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)
> 

You are right, sorry my fault:
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>

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