Re: [PATCH] usb: dwc3-exynos fix unspecified suspend clk error handling

[Bartlomiej Zolnierkiewicz]

Hi,

On Tuesday, January 10, 2017 07:36:35 AM Shuah Khan wrote:
> On 01/10/2017 07:16 AM, Shuah Khan wrote:
> > On 01/10/2017 05:05 AM, Bartlomiej Zolnierkiewicz wrote:
> >>
> >> Hi,
> >>
> >> On Monday, January 09, 2017 07:21:31 PM Shuah Khan wrote:
> >>> Fix dwc3_exynos_probe() to call clk_prepare_enable() only when suspend
> >>> clock is specified. Call clk_disable_unprepare() from remove and probe
> >>> error path only when susp_clk has been set from remove and probe error
> >>> paths.
> >>
> >> It is legal to call clk_prepare_enable() and clk_disable_unprepare()
> >> for NULL clock.  Also your patch changes susp_clk handling while
> >> leaves axius_clk handling (which also can be NULL) untouched.
> >>
> >> Do you actually see some runtime problem with the current code?
> >>
> >> If not then the patch should probably be dropped.
> >>
> >> Best regards,
> >> --
> >> Bartlomiej Zolnierkiewicz
> >> Samsung R&D Institute Poland
> >> Samsung Electronics
> > 
> > Hi Bartlomiej,
> > 
> > I am seeing the "no suspend clk specified" message in dmesg.
> > After that it sets the exynos->susp_clk = NULL and starts
> > calling clk_prepare_enable(exynos->susp_clk);
> > 
> > That can't be good. If you see the logic right above this
> > one for exynos->clk, it returns error and fails the probe.
> > This this case it doesn't, but tries to use null susp_clk.

exynos->susp_clk is optional, exynos->clk is not.

> > I believe this patch is necessary.
> 
> Let me clarify this a bit further. Since we already know
> susp_clk is null, with this patch we can avoid extra calls
> to clk_prepare_enable() and clk_disable_unprepare().
> 
> One can say, it also adds extra checks, hence I will let you
> decide one way or the other. :)

I would prefer to leave the things as they are currently.

The code in question is not performance sensitive so extra
calls are not a problem.  No extra checks means less code.

Also the current code seems to be more in line with the rest
of the kernel.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

> thanks,
> -- Shuah
> 
> > 
> > thanks,
> > -- Shuah
> > 
> >>
> >>> Signed-off-by: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
> >>> ---
> >>>  drivers/usb/dwc3/dwc3-exynos.c | 10 ++++++----
> >>>  1 file changed, 6 insertions(+), 4 deletions(-)
> >>>
> >>> diff --git a/drivers/usb/dwc3/dwc3-exynos.c b/drivers/usb/dwc3/dwc3-exynos.c
> >>> index e27899b..f97a3d7 100644
> >>> --- a/drivers/usb/dwc3/dwc3-exynos.c
> >>> +++ b/drivers/usb/dwc3/dwc3-exynos.c
> >>> @@ -131,8 +131,8 @@ static int dwc3_exynos_probe(struct platform_device *pdev)
> >>>  	if (IS_ERR(exynos->susp_clk)) {
> >>>  		dev_info(dev, "no suspend clk specified\n");
> >>>  		exynos->susp_clk = NULL;
> >>> -	}
> >>> -	clk_prepare_enable(exynos->susp_clk);
> >>> +	} else
> >>> +		clk_prepare_enable(exynos->susp_clk);
> >>>  
> >>>  	if (of_device_is_compatible(node, "samsung,exynos7-dwusb3")) {
> >>>  		exynos->axius_clk = devm_clk_get(dev, "usbdrd30_axius_clk");
> >>> @@ -196,7 +196,8 @@ static int dwc3_exynos_probe(struct platform_device *pdev)
> >>>  	regulator_disable(exynos->vdd33);
> >>>  err2:
> >>>  	clk_disable_unprepare(exynos->axius_clk);
> >>> -	clk_disable_unprepare(exynos->susp_clk);
> >>> +	if (exynos->susp_clk)
> >>> +		clk_disable_unprepare(exynos->susp_clk);
> >>>  	clk_disable_unprepare(exynos->clk);
> >>>  	return ret;
> >>>  }
> >>> @@ -210,7 +211,8 @@ static int dwc3_exynos_remove(struct platform_device *pdev)
> >>>  	platform_device_unregister(exynos->usb3_phy);
> >>>  
> >>>  	clk_disable_unprepare(exynos->axius_clk);
> >>> -	clk_disable_unprepare(exynos->susp_clk);
> >>> +	if (exynos->susp_clk)
> >>> +		clk_disable_unprepare(exynos->susp_clk);
> >>>  	clk_disable_unprepare(exynos->clk);
> >>>  
> >>>  	regulator_disable(exynos->vdd33);