linux-kernel - Re: [PATCH 1/2] dt-bindings: phy: Add Qualcomm Synopsys High-Speed USB PHY binding

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Message-ID: <20181119091523.GC10788@dragon>
Date:   Mon, 19 Nov 2018 17:15:27 +0800
From:   Shawn Guo <shawn.guo@...aro.org>
To:     Vivek Gautam <vivek.gautam@...eaurora.org>
Cc:     Rob Herring <robh@...nel.org>, kishon <kishon@...com>,
        sallenki@...eaurora.org, anur@...eaurora.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>, vkoul@...nel.org,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] dt-bindings: phy: Add Qualcomm Synopsys High-Speed
 USB PHY binding

On Mon, Nov 19, 2018 at 12:40:59PM +0530, Vivek Gautam wrote:
> On Mon, Nov 19, 2018 at 12:29 PM Shawn Guo <shawn.guo@...aro.org> wrote:
> >
> > On Sat, Nov 17, 2018 at 09:13:38AM -0600, Rob Herring wrote:
> > <snip>
> > > > > > +- qcom,init-seq:
> > > > > > +    Value type: <u32 array>
> > > > > > +    Definition: Should contain a sequence of <offset value delay> tuples to
> > > > > > +                program 'value' into phy register at 'offset' with 'delay'
> > > > > > +           in us afterwards.
> > > > >
> > > > > If we wanted this type of thing in DT, we'd have a generic binding (or
> > > > > forth).
> > > >
> > > > Right now, this is a qualcomm usb phy specific bindings - first used in
> > > > qcom,usb-hs-phy.txt and I extended it a bit for my phy.  As this is not
> > > > a so good hardware description, I'm a little hesitated to make it
> > > > generic for other platforms to use in general.  What about we put off it
> > > > a little bit until we see more platforms need the same thing?
> > >
> > > I'm not saying I want it generic. Quite the opposite. I don't think we
> > > should have it either generically or vendor specific. The main thing I
> > > have a problem with is the timing information because then we're more
> > > that just data. Without that we're talking about a bunch of properties
> > > for register fields or just raw register values in DT. That becomes
> > > more of a judgement call. There's not too much value in making a
> > > driver translate a bunch of properties just to stuff them into
> > > registers on init. But then just allowing any raw register value to be
> > > in DT could be easily abused.
> >
> > Rob,
> >
> > I agree with your comments.  Honestly, I'm not comfortable with this
> > 'qcom,init-seq' thing in the first impression.  The similar existence in
> > mainline qcom,usb-hs-phy.txt makes me think it might be acceptable with
> > the timing data added.  Okay, I know your position on this now.
> >
> > @Sriharsha,
> >
> > Seeing that 'qcom,init-seq' is being configured with the exactly same
> > values for both HS phys in SoC level dts file (qcs404.dtsi), I think
> > such settings can be moved into driver code as SoC specific data.
> > Unless you have a different view on this, I will do it with v4.
> 
> phy-qcom-qmp and phy-qcom-qusb2 have been maintaining such SoC specific
> init sequences in the drivers if you would like to have pointers from them.

Thanks for the pointer, Vivek.  That helps.

Shawn