linux-kernel - Re: [PATCH 3/3] i2c:imx: Use an hrtimer, not a timer, for checking for bus idle

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Date:   Tue, 2 Nov 2021 06:50:56 -0500
From:   Corey Minyard <minyard@....org>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>,
        Corey Minyard <cminyard@...sta.com>,
        Andrew Manley <andrew.manley@...lingtech.com>,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        Pengutronix Kernel Team <kernel@...gutronix.de>
Subject: Re: [PATCH 3/3] i2c:imx: Use an hrtimer, not a timer, for checking
 for bus idle

On Tue, Nov 02, 2021 at 09:58:06AM +0100, Uwe Kleine-König wrote:
> On Mon, Oct 04, 2021 at 07:32:16PM -0500, minyard@....org wrote:
> > From: Corey Minyard <cminyard@...sta.com>
> > 
> > The timer is too slow and significantly reduces performance.  Use an
> > hrtimer to get things working faster.
> > 
> > Signed-off-by: Corey Minyard <minyard@....org>
> > Tested-by: Andrew Manley <andrew.manley@...lingtech.com>
> > Reviewed-by: Andrew Manley <andrew.manley@...lingtech.com>
> > ---
> >  drivers/i2c/busses/i2c-imx.c | 23 +++++++++++++++--------
> >  1 file changed, 15 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
> > index 26a04dc0590b..4b0e9d1784dd 100644
> > --- a/drivers/i2c/busses/i2c-imx.c
> > +++ b/drivers/i2c/busses/i2c-imx.c
> > @@ -38,7 +38,7 @@
> >  #include <linux/iopoll.h>
> >  #include <linux/kernel.h>
> >  #include <linux/spinlock.h>
> > -#include <linux/timer.h>
> > +#include <linux/hrtimer.h>
> >  #include <linux/module.h>
> >  #include <linux/of.h>
> >  #include <linux/of_device.h>
> > @@ -53,6 +53,8 @@
> >  /* This will be the driver name the kernel reports */
> >  #define DRIVER_NAME "imx-i2c"
> >  
> > +#define I2C_IMX_CHECK_DELAY 30000 /* Time to check for bus idle, in NS */
> > +
> >  /*
> >   * Enable DMA if transfer byte size is bigger than this threshold.
> >   * As the hardware request, it must bigger than 4 bytes.\
> > @@ -214,8 +216,8 @@ struct imx_i2c_struct {
> >  	enum i2c_slave_event last_slave_event;
> >  
> >  	/* For checking slave events. */
> > -	spinlock_t	  slave_lock;
> > -	struct timer_list slave_timer;
> > +	spinlock_t     slave_lock;
> > +	struct hrtimer slave_timer;
> 
> This is unrelated to this patch, moreover it was introduced only in
> patch 1.

The second line is important for this patch, of course.  I assume you
mean the indention of the first line, which is just keeping things lined
up.

> 
> >  };
> >  
> >  static const struct imx_i2c_hwdata imx1_i2c_hwdata = {
> > @@ -783,13 +785,16 @@ static irqreturn_t i2c_imx_slave_handle(struct imx_i2c_struct *i2c_imx,
> >  	}
> >  
> >  out:
> > -	mod_timer(&i2c_imx->slave_timer, jiffies + 1);
> > +	hrtimer_try_to_cancel(&i2c_imx->slave_timer);
> 
> Don't you need to check the return value here?

Not really.  The possible return values are:

 *  *  0 when the timer was not active
 *  *  1 when the timer was active
 *  * -1 when the timer is currently executing the callback function and
 *    cannot be stopped

and if it returns 0 or 1, then everything is fine.  If it returns -1,
then the code will still work, though it may be redone (or already have
been done) by the timer function.  So it doesn't matter.

Maybe I should add a comment about this?

Thanks for reviewing.

-corey

> 
> > +	hrtimer_forward_now(&i2c_imx->slave_timer, I2C_IMX_CHECK_DELAY);
> > +	hrtimer_restart(&i2c_imx->slave_timer);
> >  	return IRQ_HANDLED;
> >  }
> >  
> 
> Best regards
> Uwe
> 
> -- 
> Pengutronix e.K.                           | Uwe Kleine-König            |
> Industrial Linux Solutions                 | https://www.pengutronix.de/ |