From: Shubhrajyoti Datta <omaplinuxkernel@xxxxxxxxx> Sent: Thursday, June 11, 2015 5:29 PM
> To: Gao Pan-B54642
> Cc: Wolfram Sang; Linux-I2C; Li Frank-B20596; Duan Fugang-B38611
> Subject: Re: [Patch v1] i2c: imx: add runtime pm support to improve the
> performance
>
> On Thu, Jun 11, 2015 at 7:20 AM, Gao Pan <b54642@xxxxxxxxxxxxx> wrote:
> > In our former i2c driver, i2c clk is enabled and disabled in xfer
> > function, which contributes to power saving. However, the clk enable
> > process brings a busy wait delay until the core is stable. As a
> > result, the performance is sacrificed.
> >
> > To weigh the power consuption and i2c bus performance, runtime pm is
> > the good solution for it. The clk is enabled when a i2c transfer
> > starts, and disabled afer a specifically defined delay.
> >
> > Without the patch the test case (many eeprom reads) executes with
> approx:
> > real 1m7.735s
> > user 0m0.488s
> > sys 0m20.040s
> >
> > With the patch the same test case (many eeprom reads) executes with
> approx:
> > real 0m54.241s
> > user 0m0.440s
> > sys 0m5.920s
> >
> > From the test result, the patch get better performance.
> >
> > Signed-off-by: Fugang Duan <B38611@xxxxxxxxxxxxx>
> > Signed-off-by: Gao Pan <b54642@xxxxxxxxxxxxx>
> > ---
> > drivers/i2c/busses/i2c-imx.c | 78
> > +++++++++++++++++++++++++++++++++++++-------
> > 1 file changed, 66 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-imx.c
> > b/drivers/i2c/busses/i2c-imx.c index 785aa67..cc4b5d6 100644
> > --- a/drivers/i2c/busses/i2c-imx.c
> > +++ b/drivers/i2c/busses/i2c-imx.c
> > @@ -53,6 +53,7 @@
> > #include <linux/platform_device.h>
> > #include <linux/sched.h>
> > #include <linux/slab.h>
> > +#include <linux/pm_runtime.h>
> >
> > /** Defines
> > ********************************************************************
> >
> > **********************************************************************
> > *********/
> > @@ -118,6 +119,8 @@
> > #define I2CR_IEN_OPCODE_0 0x0
> > #define I2CR_IEN_OPCODE_1 I2CR_IEN
> >
> > +#define I2C_PM_TIMEOUT 10 /* ms */
> > +
> > /** Variables
> > ******************************************************************
> >
> > **********************************************************************
> > *********/
> >
> > @@ -520,9 +523,6 @@ static int i2c_imx_start(struct imx_i2c_struct
> > *i2c_imx)
> >
> > i2c_imx_set_clk(i2c_imx);
> >
> > - result = clk_prepare_enable(i2c_imx->clk);
> > - if (result)
> > - return result;
> > imx_i2c_write_reg(i2c_imx->ifdr, i2c_imx, IMX_I2C_IFDR);
> > /* Enable I2C controller */
> > imx_i2c_write_reg(i2c_imx->hwdata->i2sr_clr_opcode, i2c_imx,
> > IMX_I2C_I2SR); @@ -575,7 +575,6 @@ static void i2c_imx_stop(struct
> imx_i2c_struct *i2c_imx)
> > /* Disable I2C controller */
> > temp = i2c_imx->hwdata->i2cr_ien_opcode ^ I2CR_IEN,
> > imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
> > - clk_disable_unprepare(i2c_imx->clk);
> > }
> >
> > static irqreturn_t i2c_imx_isr(int irq, void *dev_id) @@ -583,6
> > +582,9 @@ static irqreturn_t i2c_imx_isr(int irq, void *dev_id)
> > struct imx_i2c_struct *i2c_imx = dev_id;
> > unsigned int temp;
> >
> > + if (pm_runtime_suspended(i2c_imx->adapter.dev.parent))
> > + return IRQ_NONE;
> > +
>
> Didn't quite get this one.
Yes, there don't need to add pm_runtime_suspended() check in isr handler. But in some worse worse case, like system is very busy and irq is blocked by others that irq response coming is very late while i2c clock is gated off, the check can avoid system hang.
So I think it can be reasonable. How do you think ?
Regards,
Andy
��.n��������+%������w��{.n�����{��-��)�� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
