From: Uwe Kleine-König <u.kleine-koe...@pengutronix.de> Sent: Thursday, June
18, 2015 5:49 AM
> To: Gao Pan-B54642
> Cc: w...@the-dreams.de; linux-i2c@vger.kernel.org; Li Frank-B20596; Duan
> Fugang-B38611
> Subject: Re: [Patch v1] i2c: imx: add runtime pm support to improve the
> performance
>
> Hello,
>
> On Thu, Jun 11, 2015 at 09:50:04AM +0800, Gao Pan 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.
> Which platform are you referring here? Looking at i.MX21 I cannot find a
> delay for the i2c clock.
I tested platforms are i.MX6q/i.MX7d that both use i.MX21 i2c IP.
There just need one delay before disable i2c controller:
static void i2c_imx_stop(struct imx_i2c_struct *i2c_imx)
{
...
if (is_imx1_i2c(i2c_imx)) {
/*
* This delay caused by an i.MXL hardware bug.
* If no (or too short) delay, no "STOP" bit will be generated.
*/
udelay(i2c_imx->disable_delay);
}
...
/* Disable I2C controller */
temp = i2c_imx->hwdata->i2cr_ien_opcode ^ I2CR_IEN,
imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
}
>
> > To weigh the power consuption and i2c bus performance, runtime
> consumption
Thanks for your detail review, will change it in next version.
> > pm is the good solution for it. The clk is enabled when a i2c transfer
> > starts, and disabled afer a specifically defined delay.
> after
Thanks.
> > [...]
> > 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
> > [...]
> > @@ -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;
> you remove clk_prepare_enable enable and instead rely on
> clk_prepare_enable in i2c_imx_runtime_resume, right?
>
Yes, you are right.
> If I understand correctly this results in never enabling the clock if
> CONFIG_PM is disabled?!
>
Yes, you are right, I will change it in next version.
> > [...]
> > @@ -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;
> > +
> I don't claim to understand the runtime pm stuff, but I agree to the
> previous reviewer that this smells fishy. If this is required it needs a
> comment why.
>
In fact, I agree you two reviewers' consideration. As I said, this is just to
avoid system hang in worse case.
Of course, I still don't catch the worse case. So I will remove this pm stuff.
> > temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2SR);
> > if (temp & I2SR_IIF) {
> > /* save status register */
> > @@ -894,6 +896,10 @@ static int i2c_imx_xfer(struct i2c_adapter
> > *adapter,
> >
> > dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
> >
> > + result = pm_runtime_get_sync(i2c_imx->adapter.dev.parent);
> > + if (IS_ERR_VALUE(result))
> Is this better than
> + if (result < 0)
> ?
Yes, thanks.
>
> > + goto out;
> > [...]
> > @@ -1018,11 +1028,6 @@ static int i2c_imx_probe(struct platform_device
> *pdev)
> > return PTR_ERR(i2c_imx->clk);
> > }
> >
> > - ret = clk_prepare_enable(i2c_imx->clk);
> > - if (ret) {
> > - dev_err(&pdev->dev, "can't enable I2C clock\n");
> > - return ret;
> > - }
> Is there a reason the clock was enabled *here* before. With the way you
> rearranged the code the irq handler might be entered before the clock is
> on. But if I'm not mistaken (which might very well be the case) there is
> a problem also without the patch if the bootloader jumps to linux with a
> pending i2c transfer that fires when the clk_disable is done below. IMHO
> "Set up chip registers to defaults" should be done before "Request IRQ"?!
>
Agree with your opinion. I will fix it in the next version.
> > [...]
> > @@ -1093,14 +1110,51 @@ static int i2c_imx_remove(struct
> > platform_device *pdev) [...]
> > +#ifdef CONFIG_PM
> > +static int i2c_imx_runtime_suspend(struct device *dev) {
> > + struct imx_i2c_struct *i2c_imx = dev_get_drvdata(dev);
> s/ / /
> > [...]
> > +static int i2c_imx_runtime_resume(struct device *dev) {
> > + struct imx_i2c_struct *i2c_imx = dev_get_drvdata(dev);
> s/ / /
> > + int ret;
> > +
> > + ret = clk_prepare_enable(i2c_imx->clk);
> > + if (ret) {
> > + dev_err(dev, "can't enable I2C clock\n");
> > + return ret;
> > + }
> > +
> > + return 0;
> this is equivalent to:
>
> if (ret)
> dev_err(dev, "can't enable I2C clock\n");
>
> return ret;
>
> Probably a matter of taste. Also I'd suggest to add the value of ret to
> the message to make the report more useful.
>
Yes, thanks.
> > +}
> > +
> > +static const struct dev_pm_ops i2c_imx_pm_ops = {
> > + SET_RUNTIME_PM_OPS(i2c_imx_runtime_suspend,
> > + i2c_imx_runtime_resume, NULL)
> > +};
> > +#define I2C_IMX_PM_OPS (&i2c_imx_pm_ops) #else #define I2C_IMX_PM_OPS
> > +NULL #endif /* CONFIG_PM */
> > +
> > static struct platform_driver i2c_imx_driver = {
> > .probe = i2c_imx_probe,
> > .remove = i2c_imx_remove,
> > .driver = {
> > .name = DRIVER_NAME,
> > + .pm = I2C_IMX_PM_OPS,
> > .of_match_table = i2c_imx_dt_ids,
> This increases the number of styles to place the = to three. .name uses a
> tab, .of_match_table a space and you add .pm with >1 spaces.
>
Yes, thanks.
> > },
> > .id_table = imx_i2c_devtype,
> unrelated to this patch: The = in the line above is not aligned
> consistently compared to the other members at the same level like .probe.
>
Yes, thanks.
> Best regards
> Uwe
>
> --
> Pengutronix e.K. | Uwe Kleine-König
> |
> Industrial Linux Solutions | http://www.pengutronix.de/
|
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