linux-kernel - Re: [RFC 1/2] ARM: dts: exynos: update the usbdrd phy and ref clk

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Message-ID: <20171008154759.moic645jwrp7nztg@kozik-lap>
Date:   Sun, 8 Oct 2017 17:47:59 +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 1/2] ARM: dts: exynos: update the usbdrd phy and ref clk

On Sun, Oct 08, 2017 at 06:06:19PM +0530, Anand Moon wrote:
> Hi Krzysztof,
> 
> On 6 October 2017 at 12:08, Krzysztof Kozlowski <krzk@...nel.org> wrote:
> > On Fri, Oct 6, 2017 at 6:36 AM, Anand Moon <linux.amoon@...il.com> wrote:
> >> update the usbdrd link control and phy contol clks.
> >
> > The commit title and especially commit message should explain why you
> > are doing this and what are you doing. "Update" is not enough.
> > Everything could be called update.
> >
> > Therefore I do not understand the reason behind the patch.
> >
> > BR,
> > Krzysztof
> 
> so as per the driver.
> @clk: phy clock for register access
> @ref_clk: reference clock to PHY block from which PHY's operational
> clocks are derived
> 
> Both CLK_SCLK_USBPHY300 and CLK_SCLK_USBD300 belong to FSYS Clock
> and CLK_USBD300 clk is being used by the usbdrd dwc3 module.
> 
> [0] https://github.com/torvalds/linux/blob/master/drivers/clk/samsung/clk-exynos5420.c#L1040-L1053
> 
> So their is mismatch of the clk used by the usbdrd driver.

Where is the mismatch? I do not understand.

> with the above changes the driver work well with camera and disk drives
> connected to usb 3.0 ports and their is improvement in the performance.

If something is not working now, please describe it exactly so we could
both reproduce and then observe the end results of fix.

I do not understand how the change of these clocks brings improvement in
performance... ok, sometimes it might happen if the rate of clock is
being used on bus. Is this the case?

Best regards,
Krzysztof


> 
> root@...oid:~# lsusb -t
> /:  Bus 06.Port 1: Dev 1, Class=root_hub, Driver=xhci-hcd/1p, 5000M
> /:  Bus 05.Port 1: Dev 1, Class=root_hub, Driver=xhci-hcd/1p, 480M
>     |__ Port 1: Dev 3, If 0, Class=Vendor Specific Class, Driver=r8152, 480M
> /:  Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci-hcd/1p, 5000M
>     |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/2p, 5000M
>         |__ Port 1: Dev 3, If 0, Class=Mass Storage, Driver=uas, 5000M
>         |__ Port 2: Dev 4, If 0, Class=Mass Storage, Driver=uas, 5000M
> /:  Bus 03.Port 1: Dev 1, Class=root_hub, Driver=xhci-hcd/1p, 480M
>     |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/2p, 480M
> /:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=exynos-ohci/3p, 12M
> /:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=exynos-ehci/3p, 480M
> 
> Best Regards
> -Anand