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

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Date:	Tue, 26 Apr 2016 14:02:57 +0300
From:	Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
To:	Dirk Behme <dirk.behme@...bosch.com>,
	Wolfram Sang <wsa@...-dreams.de>, <linux-i2c@...r.kernel.org>
CC:	<linux-kernel@...r.kernel.org>,
	Oleksij Rempel <linux@...pel-privat.de>
Subject: Re: [PATCH] i2c: imx: use usleep_range(50,100) instead of udelay(50)

Hi Dirk,

On 26.04.2016 09:27, Dirk Behme wrote:
> From: Oleksij Rempel <linux@...pel-privat.de>
> 
> 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@...pel-privat.de>

missing your Signed-off-by.

Reviewed-by: Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>

> ---
>  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);
> 

--
With best wishes,
Vladimir