Re: [PATCH v3 2/3] phy: qcom-snps-femto-v2: add system sleep PM ops

[Adrien Thierry <athierry@redhat.com>]

Hi Bjorn,

On Thu, Jun 22, 2023 at 02:43:07PM -0700, Bjorn Andersson wrote:
> On Thu, Jun 22, 2023 at 03:40:19PM -0400, Adrien Thierry wrote:
> > The downstream driver [1] implements set_suspend(), which deals with
> > both runtime and system sleep/resume. The upstream driver already has
> > runtime PM ops, so add the system sleep PM ops as well, reusing the same
> > code as the runtime PM ops.
> > 
> > [1] https://git.codelinaro.org/clo/la/kernel/msm-5.4/-/blob/LV.AU.1.2.1.r2-05300-gen3meta.0/drivers/usb/phy/phy-msm-snps-hs.c
> > 
> > Signed-off-by: Adrien Thierry <athierry@redhat.com>
> > ---
> >  drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c | 18 ++++++++++--------
> >  1 file changed, 10 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c b/drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c
> > index ce1d2f8b568a..378a5029f61e 100644
> > --- a/drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c
> > +++ b/drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c
> > @@ -179,7 +179,7 @@ static inline void qcom_snps_hsphy_write_mask(void __iomem *base, u32 offset,
> >  	readl_relaxed(base + offset);
> >  }
> >  
> > -static int qcom_snps_hsphy_suspend(struct qcom_snps_hsphy *hsphy)
> > +static int qcom_snps_hsphy_do_suspend(struct qcom_snps_hsphy *hsphy)
> >  {
> >  	dev_dbg(&hsphy->phy->dev, "Suspend QCOM SNPS PHY\n");
> >  
> > @@ -199,7 +199,7 @@ static int qcom_snps_hsphy_suspend(struct qcom_snps_hsphy *hsphy)
> >  	return 0;
> >  }
> >  
> > -static int qcom_snps_hsphy_resume(struct qcom_snps_hsphy *hsphy)
> > +static int qcom_snps_hsphy_do_resume(struct qcom_snps_hsphy *hsphy)
> >  {
> >  	int ret;
> >  
> > @@ -214,25 +214,25 @@ static int qcom_snps_hsphy_resume(struct qcom_snps_hsphy *hsphy)
> >  	return 0;
> >  }
> >  
> > -static int __maybe_unused qcom_snps_hsphy_runtime_suspend(struct device *dev)
> > +static int __maybe_unused qcom_snps_hsphy_suspend(struct device *dev)
> >  {
> >  	struct qcom_snps_hsphy *hsphy = dev_get_drvdata(dev);
> >  
> >  	if (!hsphy->phy_initialized)
> >  		return 0;
> >  
> > -	qcom_snps_hsphy_suspend(hsphy);
> > +	qcom_snps_hsphy_do_suspend(hsphy);
> >  	return 0;
> >  }
> >  
> > -static int __maybe_unused qcom_snps_hsphy_runtime_resume(struct device *dev)
> > +static int __maybe_unused qcom_snps_hsphy_resume(struct device *dev)
> >  {
> >  	struct qcom_snps_hsphy *hsphy = dev_get_drvdata(dev);
> >  
> >  	if (!hsphy->phy_initialized)
> >  		return 0;
> >  
> > -	qcom_snps_hsphy_resume(hsphy);
> > +	qcom_snps_hsphy_do_resume(hsphy);
> >  	return 0;
> >  }
> >  
> > @@ -518,8 +518,10 @@ static const struct of_device_id qcom_snps_hsphy_of_match_table[] = {
> >  MODULE_DEVICE_TABLE(of, qcom_snps_hsphy_of_match_table);
> >  
> >  static const struct dev_pm_ops qcom_snps_hsphy_pm_ops = {
> > -	SET_RUNTIME_PM_OPS(qcom_snps_hsphy_runtime_suspend,
> > -			   qcom_snps_hsphy_runtime_resume, NULL)
> > +	SET_RUNTIME_PM_OPS(qcom_snps_hsphy_suspend,
> > +			   qcom_snps_hsphy_resume, NULL)
> > +	SET_SYSTEM_SLEEP_PM_OPS(qcom_snps_hsphy_suspend,
> > +				qcom_snps_hsphy_resume)
> 
> Won't this cause issues if you system suspend the device while it's
> already runtime suspended?
>

I'm not sure if it would cause issues, but after reflexion and discussion
with Andrew, I think it's unnecessary to add system PM ops in the femto
PHY driver. 

In the dwc3 core, both system and runtime suspend end up calling
dwc3_suspend_common(). From there, what happens depends on the USB mode
and whether the controller is entering system or runtime suspend.

HOST mode:
  (1) system suspend on a non-wakeup controller

  The [1] if branch is taken. dwc3_core_exit() is called, which ends up
  calling phy_power_off() and phy_exit(). Those two functions decrease the
  PM runtime count at some point, so they will trigger the PHY runtime sleep
  (assuming the count is right).

  (2) runtime suspend / system suspend on a wakeup controller  

  The [1] branch is not taken. dwc3_suspend_common() calls
  phy_pm_runtime_put_sync(dwc->usb2_generic_phy). Assuming the ref count is
  right, the PHY runtime suspend op is called.

DEVICE mode:

  dwc3_core_exit() is called on both runtime and system sleep
  unless the controller is already runtime suspended.

OTG mode:
  (1) system suspend : dwc3_core_exit() is called

  (2) runtime suspend : do nothing

With that in mind:

1) Does the PHY need to implement system sleep callbacks? 

dwc3 core system sleep callback will already runtime suspend the PHY, and
also call phy_power_off() and phy_exit() for non-wakeup controllers. So,
adding system PM ops to the femto PHY driver would be redundant.

2) Should the ref_clk be disabled for runtime sleep / wakeup controller
system sleep, or only for non-wakeup controller system sleep?

I'm a little hesitant here. In my submission I'm disabling it in both, but
looking at the downstream code you provided, it seems it's only disabled
for system sleep. ref_clk is disabled by phy->set_suspend() [2] which IIUC
is only called in the system sleep path through dwc3_core_exit() [3].
Moreover, in host mode the upstream code seems to make a distinction
between 1) runtime sleep / system sleep for wakeup controller, and 2)
system sleep for non-wakeup controller where phy_power_off() and
phy_exit() are only called in the latter. This suggests the PHY is not
supposed to be in a fully powered-off state for runtime sleep and system
sleep for wakeup controller. So, it's possible the ref_clk should be kept
enabled in this case. What is your take on this? I could only disable
ref_clk in the femto phy->exit() callback to keep ref_clk enabled during
runtime sleep and make sure it's only disabled on system sleep for
non-wakeup controller.

Hoping I'm not missing anything here.

Best,

Adrien

[1] https://elixir.bootlin.com/linux/latest/source/drivers/usb/dwc3/core.c#L1988
[2] https://git.codelinaro.org/clo/la/kernel/msm-5.4/-/blob/LV.AU.1.2.1.r2-05300-gen3meta.0/drivers/usb/phy/phy-msm-snps-hs.c#L524
[3] https://git.codelinaro.org/clo/la/kernel/msm-5.4/-/blob/LV.AU.1.2.1.r2-05300-gen3meta.0/drivers/usb/dwc3/core.c#L1915

> Regards,
> Bjorn
> 
> >  };
> >  
> >  static void qcom_snps_hsphy_override_param_update_val(
> > -- 
> > 2.40.1
> >