linux-kernel - [PATCH V2] media: smiapp: core: add small range to usleep

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Message-Id: <1557328313-97997-1-git-send-email-hofrat@opentech.at>
Date:   Wed,  8 May 2019 17:11:53 +0200
From:   Nicholas Mc Guire <hofrat@...ntech.at>
To:     Sakari Ailus <sakari.ailus@....fi>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nicholas Mc Guire <hofrat@...ntech.at>
Subject: [PATCH V2] media: smiapp: core: add small range to usleep_range

No need for a high-accuracy delay here as long as it is more than 2
milliseconds this should be ok - as it is non-atomic context it will
be not be precise 2 milliseconds so giving the hrtimer subsystem 50
microseconds to merge timers and reduce interrupts.

Signed-off-by: Nicholas Mc Guire <hofrat@...ntech.at>
---

Problem located by an experimental coccinelle script

V2: As Sakari Ailus <sakari.ailus@....fi> noted that the delays would be
    noticeable for the user but a range in the 50 microseconds range would
    be acceptable - the range is reduced from 2 millisecond to 50 microseconds
    which still gives the hrtimer subsystem some room for reducing interrupt
    load.

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

Patch is against 5.1 (localversion-next is next-20190508)

 drivers/media/i2c/smiapp/smiapp-quirk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/i2c/smiapp/smiapp-quirk.c b/drivers/media/i2c/smiapp/smiapp-quirk.c
index 95c0272..59cb2a5 100644
--- a/drivers/media/i2c/smiapp/smiapp-quirk.c
+++ b/drivers/media/i2c/smiapp/smiapp-quirk.c
@@ -202,7 +202,7 @@ static int jt8ev1_post_streamoff(struct smiapp_sensor *sensor)
 		return rval;
 
 	/* Wait for 1 ms + one line => 2 ms is likely enough */
-	usleep_range(2000, 2000);
+	usleep_range(2000, 2050);
 
 	/* Restore it */
 	rval = smiapp_write_8(sensor, 0x3205, 0x00);
-- 
2.1.4