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i2c: imx: reduce load by using usleep_range instead of udelay 

Documentation/timers/timers-howto.txt recommends to use
usleep_range on delays > 10usec. According to my test results
with Neonode zForce touchscreen driver, usleep_range indeed
reduces CPU load.

Stats collected with "./perf record -a -g -F 1000 sleep 10"

i2c-imx with udelay(50):
34.19% 0.00% irq/220-Neonode [kernel.kallsyms] [k] irq_thread
    ---irq_thread
       |--33.75%--irq_thread_fn
       |    |--19.27%--0x7f08a878
       |    |     i2c_master_recv
       |    |     i2c_transfer
       |    |     __i2c_transfer
       |    |     i2c_imx_xfer
       |    |     |--11.71%--i2c_imx_trx_complete
       |    |     |--5.70%--i2c_imx_start <<<<----------------
       |    |     |     |--5.38%--__timer_const_udelay
       |    |     |     |      __timer_delay
       |    |     |     |      --5.07%--read_current_timer

i2c-imx with usleep_range(50,100)
29.08% 0.00% irq/220-Neonode  [kernel.kallsyms] [k] irq_thread
    ---irq_thread
       |--28.89%--irq_thread_fn
       |    |--17.21%--0x7f08a878
       |    |     i2c_master_recv
       |    |     |--17.14%--i2c_transfer
       |    |     |     __i2c_transfer
       |    |     |     i2c_imx_xfer
       |    |     |     |--14.29%--i2c_imx_trx_complete
       |    |     |     |--1.42%--i2c_imx_start <<<<----------
       |    |     |     |      |--0.71%--usleep_range
       |    |     |     |      |--0.53%--i2c_imx_bus_busy

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
Reviewed-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
This commit is contained in:
Oleksij Rempel 2016-04-26 08:27:46 +02:00 committed by Wolfram Sang
parent 1bb1ff3e7c
commit 2b899f34e1
1 changed files with 1 additions and 1 deletions
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2
drivers/i2c/busses/i2c-imx.c
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@ -525,7 +525,7 @@ static int i2c_imx_start(struct imx_i2c_struct *i2c_imx)
imx_i2c_write_reg(i2c_imx->hwdata->i2cr_ien_opcode, i2c_imx, IMX_I2C_I2CR);
/* Wait controller to be stable */
udelay(50);
usleep_range(50, 150);
/* Start I2C transaction */
temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);