linux-kernel - Re: [PATCH v3 03/10] arm64: dts: sdm845: Introduce ADSP and CDSP PAS nodes

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Date:   Tue, 22 Jan 2019 16:40:36 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Sibi Sankar <sibis@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        devicetree@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 03/10] arm64: dts: sdm845: Introduce ADSP and CDSP PAS nodes

Hi,

On Tue, Jan 22, 2019 at 4:26 PM Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
> > > +               clocks = <&xo_board>;
> > > +               clock-names = "xo";
> >
> > I've found that nearly all the places that refer to xo_board are wrong
> > and should actually point to '<&rpmhcc RPMH_CXO_CLK>'.  Maybe yours
> > should too?
> >
>
> Yes, xo_board is a fake clock representing the 19.2MHz clock feeding the
> cxo (or cxo2) pad of the SoC. So you're definitely right in that this
> should be referencing the actual 19.2MHz clock.
>
> We've kept referring to this as xo_board, as we don't handle probe
> deferral when gcc will probe earlier than rpmcc in the boot and for
> other non-clock drivers the fear of actually hitting 0 on the refcounter
> for this (you don't want to disable the cxo while running the system).

Note that, as defined in the device tree, "xo_board" is actually 38.4.
IIUC that is not actually a fake/bogus clock but represents the actual
crystal on the board.  There's a divide by 2 in the CPU though so most
peripherals consider "xo" as 19.2.

...OK, confirmed.  The actual RF_XO_CLK pin on the board is truly
connected to 38.4.

-Doug