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

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Message-ID: <20190123010930.GI31919@minitux>
Date:   Tue, 22 Jan 2019 17:09:30 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Doug Anderson <dianders@...omium.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

On Tue 22 Jan 16:40 PST 2019, Doug Anderson wrote:

> 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.
> 

There's the 38.4MHz XO connected to the PMIC, but the signal going into
the CXO_IN pad of the SoC is supposed to come from LNBBCLK1 and be
19.2MHz.

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

And the three RF clocks from the PMIC are all ticking at 38.4MHz.


The "xo" I need here is the LNBBCLK1 (RPMH_CXO_CLK in clk-rpmh), for the
purpose of preventing the root clock to be turned off if apps goes to
suspend while the modem is booting, before it has had a chance to tell
RPM(h) that it needs it to be on.

Regards,
Bjorn