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

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Date:   Tue, 10 Jan 2017 07:36:35 -0700
From:   Shuah Khan <shuahkh@....samsung.com>
To:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     balbi@...nel.org, gregkh@...uxfoundation.org, kgene@...nel.org,
        krzk@...nel.org, javier@....samsung.com,
        linux-samsung-soc@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [PATCH] usb: dwc3-exynos fix unspecified suspend clk error
 handling

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.
> 
> 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. :)

thanks,
-- Shuah

> 
> thanks,
> -- Shuah
> 
>>
>>> Signed-off-by: Shuah Khan <shuahkh@....samsung.com>
>>> ---
>>>  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);
>>
>