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

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Date:   Mon, 22 Jan 2018 12:04:26 +0200
From:   Claudiu Beznea <Claudiu.Beznea@...rochip.com>
To:     Ladislav Michl <ladis@...ux-mips.org>
CC:     <linux-omap@...r.kernel.org>, <linux-pwm@...r.kernel.org>,
        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 22.01.2018 11:59, Ladislav Michl wrote:
> On Mon, Jan 22, 2018 at 11:00:15AM +0200, Claudiu Beznea wrote:
>>
>>
>> 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.
> 
> You mean [-1, 7] I suppose.
Right, [-1, 7], my bad. Ok, So you use -1 to disable the prescaler.

> 
>>>  		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?
> 
> Yes, as we need also some way to disable prescaler, see commit message.
> 
>>>  		l |= OMAP_TIMER_CTRL_PRE;
>>>  		l |= prescaler << 2;
>>>  	}
> 
> Best regards,
> 	ladis
>