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    SubjectRE: [PATCH 01/13] input: touchscreen: use polling mode in 88pm860x


    >-----Original Message-----
    >From: Valdis.Kletnieks@vt.edu [mailto:Valdis.Kletnieks@vt.edu]
    >Sent: 2011年4月16日 10:17 PM
    >To: Haojian Zhuang
    >Cc: haojian.zhuang@gmail.com; sameo@linux.intel.com; linux-
    >kernel@vger.kernel.org; Dmitry Torokhov
    >Subject: Re: [PATCH 01/13] input: touchscreen: use polling mode in
    >88pm860x
    >
    >On Sat, 16 Apr 2011 20:46:20 +0800, Haojian Zhuang said:
    >> Measuring point on touchscreen with IRQ mode can only monitor pen-down
    >> event. If finger is moving on touchscreen, it can't be monitored by
    >> IRQ pen-down event. So switch to polling mode after pen-down event.
    >
    >> drivers/input/touchscreen/88pm860x-ts.c | 79
    >++++++++++++++++++++++++------
    >
    >> +/*
    >> + * While 32KHz hardware timer is used for scheduler, we always assign
    >HZ
    >> + * to 128. It means that 1 tick costs 7.8msec.
    >> + */
    >> +#define MEASURE_INTERVAL_MS (7)
    >
    >Is it guaranteed that this hardware part will only ever be used on
    >systems
    >where this is true? How big a bug would it be if somebody tried to glue
    >this
    >touchscreen into some random embedded-ARM where HZ was something else,
    >and
    >should this be computed as a function of HZ instead of hardcoding 7?
    It's 7msec whatever you choose any silicon. So it's not a problem.

    >
    >It *looks* like the intent of the schedule_delayed_work() call is "let's
    >run
    >this once a tick when we're awake *anyhow*" - but looking at the code, I
    >can't
    >convince myself a rounding error in computing 'interval' won't schedule
    >1ms
    >before or after the next tick would have been. Isn't there a better API
    >with
    >slack timers or something that would do a better "next tick" job?
    >
    >

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