Re: [PATCH 8/8] [media] staging: imx: use ktime_t for timestamps
From: Steve Longerbeam
Date: Fri Dec 01 2017 - 18:55:16 EST
Hi Arnd,
This looks fine to me, except for a couple things...
On 11/27/2017 05:20 AM, Arnd Bergmann wrote:
The imx media driver passes around monotonic timestamps in the deprecated
'timespec' format. This is not a problem for the driver, as they won't
overflow, but moving to either timespec64 or ktime_t is preferred.
I'm picking ktime_t for simplicity here. frame_interval_monitor() is
the main function that changes, as it tries to compare a time interval
in microseconds. The algorithm slightly changes here, to avoid 64-bit
division. The code previously assumed that the error was at most 32-bit
worth of microseconds here, so I'm making the same assumption but add
an explicit test for it.
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
drivers/staging/media/imx/imx-media-csi.c | 8 ++------
drivers/staging/media/imx/imx-media-fim.c | 30 +++++++++++++++++-------------
drivers/staging/media/imx/imx-media.h | 2 +-
3 files changed, 20 insertions(+), 20 deletions(-)
diff --git a/drivers/staging/media/imx/imx-media-csi.c b/drivers/staging/media/imx/imx-media-csi.c
index bb1d6dafca83..26994b429cf2 100644
--- a/drivers/staging/media/imx/imx-media-csi.c
+++ b/drivers/staging/media/imx/imx-media-csi.c
@@ -207,13 +207,9 @@ static irqreturn_t csi_idmac_eof_interrupt(int irq, void *dev_id)
goto unlock;
}
- if (priv->fim) {
- struct timespec cur_ts;
-
- ktime_get_ts(&cur_ts);
+ if (priv->fim)
/* call frame interval monitor */
- imx_media_fim_eof_monitor(priv->fim, &cur_ts);
- }
+ imx_media_fim_eof_monitor(priv->fim, ktime_get());
csi_vb2_buf_done(priv);
diff --git a/drivers/staging/media/imx/imx-media-fim.c b/drivers/staging/media/imx/imx-media-fim.c
index 47275ef803f3..6df189135db8 100644
--- a/drivers/staging/media/imx/imx-media-fim.c
+++ b/drivers/staging/media/imx/imx-media-fim.c
@@ -66,7 +66,7 @@ struct imx_media_fim {
int icap_flags;
int counter;
- struct timespec last_ts;
+ ktime_t last_ts;
unsigned long sum; /* usec */
unsigned long nominal; /* usec */
@@ -147,22 +147,26 @@ static void send_fim_event(struct imx_media_fim *fim, unsigned long error)
* (presumably random) interrupt latency.
*/
static void frame_interval_monitor(struct imx_media_fim *fim,
- struct timespec *ts)
+ ktime_t timestamp)
{
- unsigned long interval, error, error_avg;
+ long long interval, error;
+ unsigned long error_avg;
bool send_event = false;
- struct timespec diff;
if (!fim->enabled || ++fim->counter <= 0)
goto out_update_ts;
- diff = timespec_sub(*ts, fim->last_ts);
- interval = diff.tv_sec * 1000 * 1000 + diff.tv_nsec / 1000;
- error = abs(interval - fim->nominal);
+ /* max error is less than l00Âs, so use 32-bit division or fail */
This comment doesn't make sense. By "max error" maybe you are referring
to the tolerance_max control, which is limited to 500 usec, but if set
to zero
(or less than tolerance_min), there is no max error, it is unbounded. Please
just remove this comment.
+ interval = ktime_to_ns(ktime_sub(timestamp, fim->last_ts));
+ error = abs(interval - NSEC_PER_USEC * (u64)fim->nominal);
+ if (error > U32_MAX)
+ error = U32_MAX;
+ else
+ error = abs((u32)error / NSEC_PER_USEC);
Why the second abs() ?
How about the following:
-ÂÂÂÂÂÂ if (error > U32_MAX)
-ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ error = U32_MAX;
-ÂÂÂÂÂÂ else
-ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ error = abs((u32)error / NSEC_PER_USEC);
+ÂÂÂÂÂÂ /* convert interval error to usec using 32-bit divide */
+ÂÂÂÂÂÂ error = (u32)min_t(long long, error, U32_MAX) / NSEC_PER_USEC;
Steve
if (fim->tolerance_max && error >= fim->tolerance_max) {
dev_dbg(fim->sd->dev,
- "FIM: %lu ignored, out of tolerance bounds\n",
+ "FIM: %llu ignored, out of tolerance bounds\n",
error);
fim->counter--;
goto out_update_ts;
@@ -184,7 +188,7 @@ static void frame_interval_monitor(struct imx_media_fim *fim,
}
out_update_ts:
- fim->last_ts = *ts;
+ fim->last_ts = timestamp;
if (send_event)
send_fim_event(fim, error_avg);
}
@@ -195,14 +199,14 @@ static void frame_interval_monitor(struct imx_media_fim *fim,
* to interrupt latency.
*/
static void fim_input_capture_handler(int channel, void *dev_id,
- struct timespec *ts)
+ ktime_t timestamp)
{
struct imx_media_fim *fim = dev_id;
unsigned long flags;
spin_lock_irqsave(&fim->lock, flags);
- frame_interval_monitor(fim, ts);
+ frame_interval_monitor(fim, timestamp);
if (!completion_done(&fim->icap_first_event))
complete(&fim->icap_first_event);
@@ -405,14 +409,14 @@ static int init_fim_controls(struct imx_media_fim *fim)
* the frame_interval_monitor() is called by the input capture event
* callback handler in that case.
*/
-void imx_media_fim_eof_monitor(struct imx_media_fim *fim, struct timespec *ts)
+void imx_media_fim_eof_monitor(struct imx_media_fim *fim, ktime_t timestamp)
{
unsigned long flags;
spin_lock_irqsave(&fim->lock, flags);
if (!icap_enabled(fim))
- frame_interval_monitor(fim, ts);
+ frame_interval_monitor(fim, timestamp);
spin_unlock_irqrestore(&fim->lock, flags);
}
diff --git a/drivers/staging/media/imx/imx-media.h b/drivers/staging/media/imx/imx-media.h
index d409170632bd..ac3ab115394f 100644
--- a/drivers/staging/media/imx/imx-media.h
+++ b/drivers/staging/media/imx/imx-media.h
@@ -280,7 +280,7 @@ int imx_media_pipeline_set_stream(struct imx_media_dev *imxmd,
/* imx-media-fim.c */
struct imx_media_fim;
-void imx_media_fim_eof_monitor(struct imx_media_fim *fim, struct timespec *ts);
+void imx_media_fim_eof_monitor(struct imx_media_fim *fim, ktime_t timestamp);
int imx_media_fim_set_stream(struct imx_media_fim *fim,
const struct v4l2_fract *frame_interval,
bool on);