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

[Bartlomiej Zolnierkiewicz]

Hi,

On Tuesday, January 10, 2017 11:23:38 PM Anand Moon wrote:
> Hi Shuah,
> 
> On 10 January 2017 at 21:58, Shuah Khan <shuahkh@xxxxxxxxxxxxxxx> wrote:
> > On 01/10/2017 09:05 AM, Bartlomiej Zolnierkiewicz wrote:
> >>
> >> 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.
> >
> > Right. That is clear since we don't fail the probe.
> >
> >>
> >>>> 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.
> >
> > What functionality is missing without the suspend clock? Would
> > it make sense to change the info. message to include what it
> > means. At the moment it doesn't anything more than "no suspend
> > clock" which is a very cryptic user visible message. It would be
> > helpful for it to also include what functionality is impacted.
> >
> 
> Both usbdrd30_susp_clk and usbdrd30_axius_clk are used by exynos5433 platform

Can you point me to the use of usbdrd30_axius_clk?

I cannot find in the upstream code.

> so moving the clk under compatible string "samsung,exynos7-dwusb3" make sense.

This is not so simple and we would probably need a new compatible for
Exynos5433 (it is currently using "samsung,exynos5250-dwusb3" one and
is not using axius_clk).

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

> Best Regards
> -Anand
> 
> > thanks,
> > -- Shuah
> >
> >>
> >> 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);