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

Claudiu Beznea
2018-01-22T10:04:32Z

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
>