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

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Message-id: <1659345.4CcVdVckN5@amdc3058>
Date:   Tue, 10 Jan 2017 19:23:43 +0100
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:     Shuah Khan <shuahkh@....samsung.com>
Cc:     Anand Moon <linux.amoon@...il.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Javier Martinez Canillas <javier@....samsung.com>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        Linux USB Mailing List <linux-usb@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3-exynos fix unspecified suspend clk error handling

On Tuesday, January 10, 2017 07:03:57 PM Bartlomiej Zolnierkiewicz wrote:
> 
> 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@....samsung.com> 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).

I also think that regardless of what is decided on making susp_clk
non-optional for some Exynos SoCs we should probably remove the debug
message as it doesn't bring useful information and may be confusing.

Shuah, can you take care of this?

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