Re: [PATCH v3 2/3] Input: snvs_pwrkey - enable snvs clock as needed

[Marco Felsch <m.felsch@pengutronix.de>]

Hi Dmitry,

On 20-07-29 23:04, Dmitry Torokhov wrote:
> On Wed, Jul 29, 2020 at 09:33:23AM +0200, Marco Felsch wrote:
> > Hi,
> > 
> > On 20-07-23 10:43, Horia Geantă wrote:
> > > From: André Draszik <git@andred.net>
> > > 
> > > At the moment, enabling this driver without the SNVS RTC driver
> > > being active will hang the kernel as soon as the power button
> > > is pressed.
> > > 
> > > The reason is that in that case the SNVS isn't enabled, and
> > > any attempt to read the SNVS registers will simply hang forever.
> > > 
> > > Ensure the clock is enabled (during the interrupt handler) to
> > > make this driver work.
> > > 
> > > Also see commit 7f8993995410 ("drivers/rtc/rtc-snvs: add clock support")
> > > and commit edb190cb1734
> > > ("rtc: snvs: make sure clock is enabled for interrupt handle")
> > > for similar updates to the snvs rtc driver.
> > > 
> > > Signed-off-by: André Draszik <git@andred.net>
> > > Reviewed-by: Horia Geantă <horia.geanta@nxp.com>
> > > Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
> > > ---
> > >  drivers/input/keyboard/snvs_pwrkey.c | 28 +++++++++++++++++++++++++++-
> > >  1 file changed, 27 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/input/keyboard/snvs_pwrkey.c b/drivers/input/keyboard/snvs_pwrkey.c
> > > index 2f5e3ab5ed63..382d2ae82c9b 100644
> > > --- a/drivers/input/keyboard/snvs_pwrkey.c
> > > +++ b/drivers/input/keyboard/snvs_pwrkey.c
> > > @@ -16,6 +16,7 @@
> > >  #include <linux/of_address.h>
> > >  #include <linux/platform_device.h>
> > >  #include <linux/pm_wakeirq.h>
> > > +#include <linux/clk.h>
> > >  #include <linux/mfd/syscon.h>
> > >  #include <linux/regmap.h>
> > >  
> > > @@ -38,6 +39,7 @@ struct pwrkey_drv_data {
> > >  	int wakeup;
> > >  	struct timer_list check_timer;
> > >  	struct input_dev *input;
> > > +	struct clk *clk;
> > >  	u8 minor_rev;
> > >  };
> > >  
> > > @@ -47,7 +49,10 @@ static void imx_imx_snvs_check_for_events(struct timer_list *t)
> > >  	struct input_dev *input = pdata->input;
> > >  	u32 state;
> > >  
> > > +	clk_enable(pdata->clk);
> > >  	regmap_read(pdata->snvs, SNVS_HPSR_REG, &state);
> > > +	clk_disable(pdata->clk);
> > > +
> > >  	state = state & SNVS_HPSR_BTN ? 1 : 0;
> > >  
> > >  	/* only report new event if status changed */
> > > @@ -74,11 +79,13 @@ static irqreturn_t imx_snvs_pwrkey_interrupt(int irq, void *dev_id)
> > >  
> > >  	pm_wakeup_event(input->dev.parent, 0);
> > >  
> > > +	clk_enable(pdata->clk);
> > > +
> > >  	regmap_read(pdata->snvs, SNVS_LPSR_REG, &lp_status);
> > >  	if (lp_status & SNVS_LPSR_SPO) {
> > >  		if (pdata->minor_rev == 0) {
> > >  			/*
> > > -			 * The first generation i.MX6 SoCs only sends an
> > > +			 * The first generation i.MX[6|7] SoCs only send an
> > >  			 * interrupt on button release. To mimic power-key
> > >  			 * usage, we'll prepend a press event.
> > >  			 */
> > > @@ -96,6 +103,8 @@ static irqreturn_t imx_snvs_pwrkey_interrupt(int irq, void *dev_id)
> > >  	/* clear SPO status */
> > >  	regmap_write(pdata->snvs, SNVS_LPSR_REG, SNVS_LPSR_SPO);
> > >  
> > > +	clk_disable(pdata->clk);
> > 
> > I'm not so happy about clk_enable/disable() during the interrupt
> > routine since those routines should be handled fast. Since we assume
> > that the clock is always oni
> 
> We do? I thought that the fact that clock might be off is the root of
> the problem.

Currently yes else the driver would never work. I thought so at least
after reading the commit message. But after checking the imx6qdl I
found that the imx6qdl has no clock-gate for the SNVS module. I think
Horia had Problems on a imx7 device since he adapted the comment to
cover the imx7. Which makes more sense since the imx7 has a clock gate
but the commit message is wrong. After checking the device-tree's in
mainline all imx7 and imx8 devices specify the "snvs-pwrkey" clock so
this is a new feature and they need the clock. So IMHO for those devices
a clock should be required and not optional.

> > I would rather call clk_prepare_enable()
> > during probe() and keep the clock on.
> 
> clk_enable() must not sleep and is supposed to be lightweight. This
> interrupt I believe is supposed to be infrequent, so having it here
> should be fine and might save us some power.

Didn't know that clk_enable()/clk_disable() never sleeps and yes it
should be infrequent triggered. I don't think that we can save a
measureable amount of power since this is Low-Power IP clocked by a
low-power clock. However, this was just my point of view.

> > > +
> > >  	return IRQ_HANDLED;
> > >  }
> > >  
> > > @@ -140,6 +149,23 @@ static int imx_snvs_pwrkey_probe(struct platform_device *pdev)
> > >  	if (pdata->irq < 0)
> > >  		return -EINVAL;
> > >  
> > > +	pdata->clk = devm_clk_get_optional(&pdev->dev, "snvs-pwrkey");
> > > +	if (IS_ERR(pdata->clk))
> > > +		return PTR_ERR(pdata->clk);
> > > +
> > > +	error = clk_prepare(pdata->clk);
> > > +	if (error) {
> > > +		dev_err(&pdev->dev, "failed to prepare the snvs clock\n");
> > > +		return error;
> > > +	}
> > > +	error = devm_add_action_or_reset(&pdev->dev,
> > > +			(void(*)(void *))clk_unprepare,
> > > +			pdata->clk);
> > 
> > I'm not a fan about those casts. However, the intentation should be
> > fixed.
> 
> Yes, can we please create a proper function for this (or maybe we will
> finally get devm clk API?).

devm_clk API +1 :)

Regards,
  Marco