Message-id: <5156028.4V9iLD3Qkj@amdc3058>
Date:   Tue, 10 Jan 2017 18:09:40 +0100
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:     Shuah Khan <shuahkh@....samsung.com>
Cc:     linux-arm-kernel@...ts.infradead.org, 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,
        Vivek Gautam <vivek.gautam@...eaurora.org>
Subject: Re: [PATCH] usb: dwc3-exynos fix unspecified suspend clk error handling


Hi,

On Tuesday, January 10, 2017 09:28:52 AM Shuah Khan 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.

Well, all I know is what the original commit descriptions says and
that the commit itself comes from patchset adding Exynos7 USB 3.0
support [1]:

commit 72d996fc7a01c2e4d581a15db7d001e2799ffb29
Author: Vivek Gautam <gautam.vivek@...sung.com>
Date:   Fri Nov 21 19:05:46 2014 +0530

    usb: dwc3: exynos: Add provision for suspend clock
    
    DWC3 controller on Exynos SoC series have separate control for
    suspend clock which replaces pipe3_rx_pclk as clock source to
    a small part of DWC3 core that operates when SS PHY is in its
    lowest power state (P3) in states SS.disabled and U3.
    
    Suggested-by: Anton Tikhomirov <av.tikhomirov@...sung.com>
    Signed-off-by: Vivek Gautam <gautam.vivek@...sung.com>
    Signed-off-by: Felipe Balbi <balbi@...com>

Anton's & Vivek's Samsung email addresses are no longer valid but
I added current Vivek's email address to Cc:.

BTW What is interesting is that the Exynos7 dts patch [2] has never
made it into upstream for some reason.  In the meantime however
Exynos5433 (similar to Exynos7 to some degree) became the user of
susp_clk.

[1] https://lkml.org/lkml/2014/11/21/247
[2] https://patchwork.kernel.org/patch/5355161/

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

> thanks,
> -- Shuah
> 
> > 
> > Best regards,
> > --
> > Bartlomiej Zolnierkiewicz
> > Samsung R&D Institute Poland
> > Samsung Electronics
> > 
> >> 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);

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