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Subject: Re: [PATCH 1/3] clocksource: timer-dm: Check prescaler value
To:     Ladislav Michl <ladis@linux-mips.org>
CC:     <linux-omap@vger.kernel.org>, <linux-pwm@vger.kernel.org>,
        Keerthy <j-keerthy@ti.com>, <daniel.lezcano@linaro.org>,
        <thierry.reding@gmail.com>, <tony@atomide.com>,
        <aaro.koskinen@iki.fi>, <narmstrong@baylibre.com>,
        <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <sebastian.reichel@collabora.co.uk>, <robh+dt@kernel.org>,
        <t-kristo@ti.com>, <grygorii.strashko@ti.com>
References: <20180117214629.GA11952@lenoch> <20180117214714.GB11952@lenoch>
 <4688ef73-99ac-1295-2e3b-ed79e8670262@microchip.com>
 <20180122095950.GA19401@lenoch>
From:   Claudiu Beznea <Claudiu.Beznea@microchip.com>
Message-ID: <62985c64-b05c-e3ae-2473-6b0f20dd71b3@microchip.com>
Date:   Mon, 22 Jan 2018 12:04:26 +0200
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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@linux-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
>