i2c: s3c2410: Remove recently introduced performance overheads
authorMark Brown <broonie@opensource.wolfsonmicro.com>
Wed, 21 Nov 2012 04:12:11 +0000 (13:12 +0900)
committerWolfram Sang <w.sang@pengutronix.de>
Thu, 22 Nov 2012 21:34:40 +0000 (22:34 +0100)
commit31f313d9bebfc17e48c787c8c36b38662b4134a1
tree7fcd40d17bac586a95ae21ed9f54fa0e642b4711
parentc5d5474425c4e7e291a98e739ea65f8acd0d8d5c
i2c: s3c2410: Remove recently introduced performance overheads

The changes in "i2c-s3c2410: use exponential back off while polling for
bus idle" remove the initial busy wait for I2C transfers to complete and
replace it with usleep_range() calls which will schedule.

Since for older SoCs I2C transfers would usually complete within an
extremely small number of CPU cycles there is a win from not having to
schedule.  This happens because on the older SoCs the cores run at a
smaller multiple of the speeds that the I2C bus is operating at; on more
modern SoCs the busy wait is less likely to be effective.

Fix the issue by restoring the busy wait, reducing the number of spins
from 20 to 3 which covers the overwhelming majority of I2C transfers on
the SoCs where the busy wait is effective.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Olof Johansson <olof@lixom.net>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
drivers/i2c/busses/i2c-s3c2410.c