linux-kernel - Re: [PATCH 1/3] clocksource: timer-dm: Check prescaler value

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Date:   Mon, 22 Jan 2018 11:00:15 +0200
From:   Claudiu Beznea <Claudiu.Beznea@...rochip.com>
To:     Ladislav Michl <ladis@...ux-mips.org>,
        <linux-omap@...r.kernel.org>, <linux-pwm@...r.kernel.org>
CC:     Keerthy <j-keerthy@...com>, <daniel.lezcano@...aro.org>,
        <thierry.reding@...il.com>, <tony@...mide.com>,
        <aaro.koskinen@....fi>, <narmstrong@...libre.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <sebastian.reichel@...labora.co.uk>, <robh+dt@...nel.org>,
        <t-kristo@...com>, <grygorii.strashko@...com>
Subject: Re: [PATCH 1/3] clocksource: timer-dm: Check prescaler value



On 17.01.2018 23:47, Ladislav Michl wrote:
> Invalid value silently disables use of the prescaler.
> Use -1 explicitely for that purpose and error out on
> invalid value.
> 
> Signed-off-by: Ladislav Michl <ladis@...ux-mips.org>
> ---
>  drivers/clocksource/timer-dm.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clocksource/timer-dm.c b/drivers/clocksource/timer-dm.c
> index 60db1734ea3b..324ec93d3dd2 100644
> --- a/drivers/clocksource/timer-dm.c
> +++ b/drivers/clocksource/timer-dm.c
> @@ -663,13 +663,13 @@ int omap_dm_timer_set_prescaler(struct omap_dm_timer *timer, int prescaler)
>  {
>  	u32 l;
>  
> -	if (unlikely(!timer))
> +	if (unlikely(!timer) || prescaler < -1 || prescaler > 7)
You are checking the prescaller here to be in [0, 7] interval.
>  		return -EINVAL;
>  
>  	omap_dm_timer_enable(timer);
>  	l = omap_dm_timer_read_reg(timer, OMAP_TIMER_CTRL_REG);
>  	l &= ~(OMAP_TIMER_CTRL_PRE | (0x07 << 2));
> -	if (prescaler >= 0x00 && prescaler <= 0x07) {
> +	if (prescaler >= 0) {
Is this check still necessary?
>  		l |= OMAP_TIMER_CTRL_PRE;
>  		l |= prescaler << 2;
>  	}
>