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

[Anand Moon]

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

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);
>>
>
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