Re: [PATCH] i2c: imx: use usleep_range(50,100) instead of udelay(50)

[Dirk Behme]

On 26.04.2016 13:02, Vladimir Zapolskiy wrote:
> Hi Dirk,
>
> On 26.04.2016 09:27, Dirk Behme wrote:
> > From: Oleksij Rempel <linux@xxxxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxxxxx>


Signed-off-by: Dirk Behme <dirk.behme@xxxxxxxxxxxx>


> missing your Signed-off-by.
>
> Reviewed-by: Vladimir Zapolskiy <vladimir_zapolskiy@xxxxxxxxxx>
>
> > ---
> >   drivers/i2c/busses/i2c-imx.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
> > index 1ca7ef2..1844bc9 100644
> > --- a/drivers/i2c/busses/i2c-imx.c
> > +++ b/drivers/i2c/busses/i2c-imx.c
> > @@ -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);