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SubjectRe: [PATCH 1/3] media: smiapp: core: add range to usleep_range
Hi Nicholas,

On Sun, Apr 07, 2019 at 04:16:02AM +0200, Nicholas Mc Guire wrote:
> Allow the hrtimer subsystem to coalesce delay timers of lower accuracy
> by providing a suitable range
>
> Signed-off-by: Nicholas Mc Guire <hofrat@opentech.at>
> ---
>
> Problem located by an experimental coccinelle script
>
> hrtimers in atomic context have limited accuracy due to possible
> context-switching and interruption so the accuracy is limited
> anyway. Giving the hrtimer subsystem a reasonable range for merging
> hrtimers helps to reduce the load on the hrtimer subsystem. As this
> delays do not seem to mandate high accuracy the range of a factor
> two seems acceptable.
>
> Patch was compile tested with: x86_64_defconfig + MEDIA_SUPPORT=m,
> MEDIA_CAMERA_SUPPORT=y, MEDIA_CONTROLLER=y, VIDEO_V4L2_SUBDEV_API=y,
> VIDEO_SMIAPP=m
> (with a number of sparse warnings on sizeof() usage)
>
> Patch is against 5.1-rc3 (localversion-next is next-20190405)

The delays are exact for the reason that they are user-visible delays in
image capturing related use cases. Sometimes milliseconds matter, or at
least adding more does not help.

>
> drivers/media/i2c/smiapp/smiapp-core.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/media/i2c/smiapp/smiapp-core.c b/drivers/media/i2c/smiapp/smiapp-core.c
> index 58a45c3..c0c29ec 100644
> --- a/drivers/media/i2c/smiapp/smiapp-core.c
> +++ b/drivers/media/i2c/smiapp/smiapp-core.c
> @@ -1222,19 +1222,19 @@ static int smiapp_power_on(struct device *dev)
> dev_err(&client->dev, "failed to enable vana regulator\n");
> return rval;
> }
> - usleep_range(1000, 1000);
> + usleep_range(1000, 2000);
>
> rval = clk_prepare_enable(sensor->ext_clk);
> if (rval < 0) {
> dev_dbg(&client->dev, "failed to enable xclk\n");
> goto out_xclk_fail;
> }
> - usleep_range(1000, 1000);
> + usleep_range(1000, 2000);
>
> gpiod_set_value(sensor->xshutdown, 1);
>
> sleep = SMIAPP_RESET_DELAY(sensor->hwcfg->ext_clk);
> - usleep_range(sleep, sleep);
> + usleep_range(sleep, sleep*2);
>
> mutex_lock(&sensor->mutex);
>
> @@ -1381,7 +1381,7 @@ static int smiapp_power_off(struct device *dev)
>
> gpiod_set_value(sensor->xshutdown, 0);
> clk_disable_unprepare(sensor->ext_clk);
> - usleep_range(5000, 5000);
> + usleep_range(5000, 10000);
> regulator_disable(sensor->vana);
> sensor->streaming = false;
>

--
Sakari Ailus

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