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From:   Stephen Boyd <sboyd@kernel.org>
To:     Rob Clark <robdclark@chromium.org>
Cc:     Matthias Kaehlcke <mka@chromium.org>,
        Taniya Das <tdas@codeaurora.org>,
        Michael Turquette <mturquette@baylibre.com>,
        David Brown <david.brown@linaro.org>,
        Rajendra Nayak <rnayak@codeaurora.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        linux-soc@vger.kernel.org, linux-clk@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>, devicetree@vger.kernel.org,
        robh@kernel.org, Rob Herring <robh+dt@kernel.org>,
        Jordan Crouse <jcrouse@codeaurora.org>,
        Jeykumar Sankaran <jsanka@codeaurora.org>,
        Sean Paul <seanpaul@chromium.org>
Subject: Re: [PATCH v4 5/5] clk: qcom: Add Global Clock controller (GCC) driver for SC7180
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Date:   Fri, 08 Nov 2019 13:14:09 -0800
Message-Id: <20191108211410.0411720869@mail.kernel.org>
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Quoting Rob Clark (2019-11-08 11:40:53)
> On Fri, Nov 8, 2019 at 10:42 AM Stephen Boyd <sboyd@kernel.org> wrote:
> >
> > So the scenario is DT describes the clk
> >
> >  dpu_node {
> >      clocks =3D <&cc AHB_CLK>;
> >      clock-names =3D "iface";
> >  }
> >
> > but the &cc node has a driver that doesn't probe?
> >
> > I believe in this scenario we return -EPROBE_DEFER because we assume we
> > should wait for the clk driver to probe and provide the iface clk. See
> > of_clk_get_hw_from_clkspec() and how it looks through a list of clk
> > providers and tries to match the &cc phandle to some provider.
> >
> > Once the driver probes, the match will happen and we'll be able to look
> > up the clk in the provider with __of_clk_get_hw_from_provider(). If
> > the clk provider decides that there isn't a clk object, it will return
> > NULL and then eventually clk_hw_create_clk() will turn the NULL return
> > value into a NULL pointer to return from clk_get().
> >
>=20
> ok, that was the scenario I was worried about (since unclk'd register
> access tends to be insta-reboot and hard to debug)..  so I think it
> should be ok to make dpu just ignore NULL clks.
>=20
> From a quick look, I think something like the attached (untested).
> (Sorry, I'd just paste it inline but gmail somehow eats all the
> whitespace when I do that :-/)

Cool. Looks good to me.