linux-kernel - Re: [RFC 2/2] phy: exynos5-usbdrd: remove disable and enable of phy clk

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Date:   Sun, 8 Oct 2017 17:50:15 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Anand Moon <linux.amoon@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Kukjin Kim <kgene@...nel.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Lee Jones <lee.jones@...aro.org>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Andrzej Pietrasiewicz <andrzej.p@...sung.com>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 2/2] phy: exynos5-usbdrd: remove disable and enable of phy
 clk

On Sun, Oct 08, 2017 at 06:11:12PM +0530, Anand Moon wrote:
> Hi Krzysztof,
> 
> On 6 October 2017 at 12:12, Krzysztof Kozlowski <krzk@...nel.org> wrote:
> > On Fri, Oct 6, 2017 at 6:36 AM, Anand Moon <linux.amoon@...il.com> wrote:
> >> remove the disable and enable of phy clk.
> >> phy clk is needed to tune the phy controller.
> >
> > Drivers should in general enable and disable the clocks they use. Just
> > like in patch #1 please describe why you are doing this, what kind of
> > problem are you trying to solve and what exactly are you trying to do
> > here.
> >
> > BR,
> > Krzysztof
> >
> 
> [snip]
> 
> Usually we would disable the clk on error patch and return with failed.
> but in the current code we disable the clk in init routine and
> enable the clk in disable routine which seem incorrect.

No. For example for exynos5_usbdrd_phy_exit() the driver enables the
clock only for the access to PHY block (PHY registers).

> 
> [0] https://github.com/torvalds/linux/blob/master/drivers/phy/samsung/phy-exynos5-usbdrd.c#L362-L412
> [1] https://github.com/torvalds/linux/blob/master/drivers/phy/samsung/phy-exynos5-usbdrd.c#L424-L446
> 
> On 3.10.x kernel clk_summary all the clk are enables.
> 
>     mout_usbdrd300              3           3            24000000
>        dout_usbdrd300           2           2            24000000
>           sclk_usbdrd300        1           1            24000000
>        dout_usbphy300           2           2            24000000
>           sclk_usbphy300        1           1            24000000
>     mout_usbdrd301              3           3            24000000
>        dout_usbdrd301           2           2            24000000
>           sclk_usbdrd301        1           1            24000000
>        dout_usbphy301           2           2            24000000
>           sclk_usbphy301        1           1            24000000
> 
> Some more changes in clk driver might be required to stabilize the usb module.

Please describe the issues with stability first.

Best regards,
Krzysztof