[PATCH v4] iio: adc: ti-ads1298: Fix incorrect timeout comment

[Md Shofiqul Islam <shofiqtest@gmail.com>]

At the lowest supported data rate of 250Hz, one conversion period is
4ms, not 40ms. The 50ms timeout is deliberately conservative to allow
for kernel scheduling latency, which can be significant under load or
on slow machines.

Fix the comment to state the correct conversion time, use "lowest sample
rate" for clarity, and explain that the extra margin exists to absorb
scheduling latency so that no one is tempted to shrink the timeout to
match the conversion period.

Also drop the redundant ret variable assignment by using the return value
of wait_for_completion_timeout() directly in the if() condition.

Signed-off-by: Md Shofiqul Islam <shofiqtest@gmail.com>
---
Changes in v4:
 - Drop the ret assignment for wait_for_completion_timeout(); use the
   return value directly in the if() condition (Andy Shevchenko)

Changes in v3:
 - Fix multi-line comment style: move comment text to its own line
   after '/*' (Andy Shevchenko)

Changes in v2:
 - Correct conversion time to 4ms (was wrong 40ms), add scheduling
   latency explanation, clarify "lowest sample rate" (David Lechner,
   Andy Shevchenko)

 drivers/iio/adc/ti-ads1298.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/ti-ads1298.c b/drivers/iio/adc/ti-ads1298.c
index ae30b47e45..25261163d3 100644
--- a/drivers/iio/adc/ti-ads1298.c
+++ b/drivers/iio/adc/ti-ads1298.c
@@ -210,9 +210,11 @@ static int ads1298_read_one(struct ads1298_private *priv, int chan_index)
 		return ret;
 	}
 
-	/* Cannot take longer than 40ms (250Hz) */
-	ret = wait_for_completion_timeout(&priv->completion, msecs_to_jiffies(50));
-	if (!ret)
+	/*
+	 * One conversion takes at most 4ms at the lowest sample rate (250Hz).
+	 * Use 50ms to allow for kernel scheduling latency.
+	 */
+	if (!wait_for_completion_timeout(&priv->completion, msecs_to_jiffies(50)))
 		return -ETIMEDOUT;
 
 	return 0;
-- 
2.54.0.windows.1