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

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

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?

Regards,
Matthias

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