[PATCH RFC 1/2] phy: qcom-snps-femto-v2: properly enable ref clock

[Bjorn Andersson]

On Tue, May 30, 2023 at 02:46:05PM -0400, Adrien Thierry wrote:
> Hi Bjorn, thanks for your reply!
> 
> On Mon, May 29, 2023 at 02:16:29PM -0700, Bjorn Andersson wrote:
> > On Mon, May 29, 2023 at 02:56:36PM -0400, Adrien Thierry wrote:
> > > The driver is not enabling the ref clock, which thus gets disabled by
> > > the clk_disable_unused initcall. This leads to the dwc3 controller
> > > failing to initialize if probed after clk_disable_unused is called, for
> > > instance when the driver is built as a module.
> > > 
> > 
> > Good catch!
> > 
> > A side note though, clk_disable_unused() has no way to take kernel
> > modules into consideration today, and it doesn't handle the case where
> > clock drivers are built as modules appropriately.
> > Work has started to address this, but as of todaybooting the system
> > without clk_ignore_unused is not recommended...
> >
> 
> For my understanding, do you have an example of a situation that would
> fail with modules when not using clk_ignore_unused?
> 

The prime example relates to the display clocks, where the bootloader
typically leave clocks on and at lateinit we haven't yet loaded enough
modules to bring up the display. And to make matters worse, the code
ends up disabling the PLL feeding the clock tree without first disabling
some of the muxes - which has side effects...

Another case, although much less concerning in the short run, is when
you have any of the clock drivers built as modules. clk_disable_unused()
will be invoked before they are loaded, so your expectation that unused
clocks are turned off is just not fulfilled.

> > > To fix this, add calls to clk_prepare_enable/clk_disable_unprepare at
> > > the proper places.
> > > 
> > 
> > If I parse the downstream kernel correctly the refclock should be
> > turned off across runtime and system suspend as well.
> > 
> 
> Which downstream kernel are you using? I'm not seing a system suspend
> callback in mine [1]. refclock should be turned off on runtime suspend in
> my patch, in qcom_snps_hsphy_suspend, which is called by
> qcom_snps_hsphy_runtime_suspend.
> 

Forgive me, but isn't [1] the driver you're modifying?

I'm looking at [2], with set_suspend() being invoked from the runtime
and system suspend/resume handlers.

> [1] https://git.codelinaro.org/clo/la/kernel/ark-5.14/-/blob/kernel.lnx.5.14.r2-rel/drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c

[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#L908

Regards,
Bjorn

> 
> > Regards,
> > Bjorn
> > 
> > > Signed-off-by: Adrien Thierry <athierry at redhat.com>
> > > ---
> > >  drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c | 20 +++++++++++++++++--
> > >  1 file changed, 18 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c b/drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c
> > > index 6c237f3cc66d..8abf482e81a8 100644
> > > --- a/drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c
> > > +++ b/drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c
> > > @@ -166,6 +166,7 @@ static int qcom_snps_hsphy_suspend(struct qcom_snps_hsphy *hsphy)
> > >  	}
> > >  
> > >  	clk_disable_unprepare(hsphy->cfg_ahb_clk);
> > > +	clk_disable_unprepare(hsphy->ref_clk);
> > >  	return 0;
> > >  }
> > >  
> > > @@ -181,6 +182,12 @@ static int qcom_snps_hsphy_resume(struct qcom_snps_hsphy *hsphy)
> > >  		return ret;
> > >  	}
> > >  
> > > +	ret = clk_prepare_enable(hsphy->ref_clk);
> > > +	if (ret) {
> > > +		dev_err(&hsphy->phy->dev, "failed to enable ref clock\n");
> > > +		return ret;
> > > +	}
> > > +
> > >  	return 0;
> > >  }
> > >  
> > > @@ -380,10 +387,16 @@ static int qcom_snps_hsphy_init(struct phy *phy)
> > >  		goto poweroff_phy;
> > >  	}
> > >  
> > > +	ret = clk_prepare_enable(hsphy->ref_clk);
> > > +	if (ret) {
> > > +		dev_err(&phy->dev, "failed to enable ref clock, %d\n", ret);
> > > +		goto disable_ahb_clk;
> > > +	}
> > > +
> > >  	ret = reset_control_assert(hsphy->phy_reset);
> > >  	if (ret) {
> > >  		dev_err(&phy->dev, "failed to assert phy_reset, %d\n", ret);
> > > -		goto disable_ahb_clk;
> > > +		goto disable_ref_clk;
> > >  	}
> > >  
> > >  	usleep_range(100, 150);
> > > @@ -391,7 +404,7 @@ static int qcom_snps_hsphy_init(struct phy *phy)
> > >  	ret = reset_control_deassert(hsphy->phy_reset);
> > >  	if (ret) {
> > >  		dev_err(&phy->dev, "failed to de-assert phy_reset, %d\n", ret);
> > > -		goto disable_ahb_clk;
> > > +		goto disable_ref_clk;
> > >  	}
> > >  
> > >  	qcom_snps_hsphy_write_mask(hsphy->base, USB2_PHY_USB_PHY_CFG0,
> > > @@ -448,6 +461,8 @@ static int qcom_snps_hsphy_init(struct phy *phy)
> > >  
> > >  	return 0;
> > >  
> > > +disable_ref_clk:
> > > +	clk_disable_unprepare(hsphy->ref_clk);
> > >  disable_ahb_clk:
> > >  	clk_disable_unprepare(hsphy->cfg_ahb_clk);
> > >  poweroff_phy:
> > > @@ -462,6 +477,7 @@ static int qcom_snps_hsphy_exit(struct phy *phy)
> > >  
> > >  	reset_control_assert(hsphy->phy_reset);
> > >  	clk_disable_unprepare(hsphy->cfg_ahb_clk);
> > > +	clk_disable_unprepare(hsphy->ref_clk);
> > >  	regulator_bulk_disable(ARRAY_SIZE(hsphy->vregs), hsphy->vregs);
> > >  	hsphy->phy_initialized = false;
> > >  
> > > -- 
> > > 2.40.1
> > >
> 
> Best,
> Adrien
>