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?
> 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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