On Fri, Jan 13, 2017 at 12:07:45PM -0800, Dmitry Torokhov wrote:
> On Fri, Jan 13, 2017 at 08:57:36PM +0100, Nicholas Mc Guire wrote:
> > Using counter based retry loops for peripherals results in the delay
> > being significantly overrun during high-load situations where delay
> > functions tend to be vary imprecise and overrun there timeouts. So
> > condition the termination on the actual condition of 2s for the
> > re-calibration to have been successful.
> >
> > As this is a very long delay there is no advantage in using
> > high-resolution timers thus switching this to msleep().
> >
> > Signed-off-by: Nicholas Mc Guire <hofrat@xxxxxxxxx>
> > ---
> > Problem detected with coccinelle script (usleep_range for long delay)
> >
> > The basic model for the fix up here is to use
> >
> > timeout = jiffies + (retry_time)
> > do {
> > check()
> > mleep()
> > } while (time_is_after_jiffies(timeout));
> >
> > rather than using a counter and have very long retry loops under load
> > conditions. In the specific case it is sleep()/check() though to wait
> > on the previous write to complete. The initial intent was to move the
> > usleep_range() to msleep() as the delays are very long - if this
> > refactoring of the timeout loop is desirable or not is not clear (both
> > time and count based models seem to be common).
> >
> > Patch was compile tested with: x86_64_defconfig + CONFIG_MOUSE_CYAPA=m
> >
> > Patch is against 4.10-rc3 (localversion-next is next-20170113)
> >
> > drivers/input/mouse/cyapa_gen3.c | 27 ++++++++++++---------------
> > 1 file changed, 12 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/input/mouse/cyapa_gen3.c b/drivers/input/mouse/cyapa_gen3.c
> > index f9600753..0c544de 100644
> > --- a/drivers/input/mouse/cyapa_gen3.c
> > +++ b/drivers/input/mouse/cyapa_gen3.c
> > @@ -789,7 +789,7 @@ static ssize_t cyapa_gen3_do_calibrate(struct device *dev,
> > const char *buf, size_t count)
> > {
> > struct cyapa *cyapa = dev_get_drvdata(dev);
> > - int tries;
> > + unsigned long timeout;
> > int ret;
> >
> > ret = cyapa_read_byte(cyapa, CYAPA_CMD_DEV_STATUS);
> > @@ -812,31 +812,28 @@ static ssize_t cyapa_gen3_do_calibrate(struct device *dev,
> > goto out;
> > }
> >
> > - tries = 20; /* max recalibration timeout 2s. */
> > + /* max recalibration timeout 2s. */
> > + timeout = jiffies + 20 * HZ;
>
> Doesn't this make timeout 20 sec instead of 2?
yes - my bad - that should have been 2
>
> > do {
> > /*
> > * For this recalibration, the max time will not exceed 2s.
> > * The average time is approximately 500 - 700 ms, and we
> > * will check the status every 100 - 200ms.
> > */
> > - usleep_range(100000, 200000);
> > -
> > + msleep(100);
> > ret = cyapa_read_byte(cyapa, CYAPA_CMD_DEV_STATUS);
> > if (ret < 0) {
> > - dev_err(dev, "Error reading dev status: %d\n",
> > - ret);
> > + dev_err(dev, "Error reading dev status: %d\n", ret);
> > goto out;
> > }
> > - if ((ret & CYAPA_DEV_NORMAL) == CYAPA_DEV_NORMAL)
> > - break;
> > - } while (--tries);
> > + if ((ret & CYAPA_DEV_NORMAL) == CYAPA_DEV_NORMAL) {
> > + dev_dbg(dev, "Calibration successful.\n");
> > + goto out;
> > + }
> > + } while (time_is_after_jiffies(timeout));
> >
> > - if (tries == 0) {
> > - dev_err(dev, "Failed to calibrate. Timeout.\n");
> > - ret = -ETIMEDOUT;
> > - goto out;
> > - }
> > - dev_dbg(dev, "Calibration successful.\n");
> > + dev_err(dev, "Failed to calibrate. Timeout.\n");
> > + ret = -ETIMEDOUT;
> >
> > out:
> > return ret < 0 ? ret : count;
> > --
> > 2.1.4
> >
>
> --
> Dmitry
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