From: Matthias Kaehlcke <mka@chromium.org>
To: Rob Clark <robdclark@gmail.com>
Cc: Rob Clark <robdclark@chromium.org>,
Stephen Boyd <sboyd@kernel.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>,
"open list:ARM/QUALCOMM SUPPORT" <linux-soc@vger.kernel.org>,
linux-clk <linux-clk@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>, Rob Herring <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
Date: Thu, 14 Nov 2019 09:04:49 -0800 [thread overview]
Message-ID: <20191114170449.GG27773@google.com> (raw)
In-Reply-To: <CAF6AEGv9+Ow=RCXGKmaANfmA2NtR32E07CKwGFKJbeeOJRP9=Q@mail.gmail.com>
On Wed, Nov 13, 2019 at 09:30:57PM -0800, Rob Clark wrote:
> On Wed, Nov 13, 2019 at 5:03 PM Matthias Kaehlcke <mka@chromium.org> wrote:
> >
> > On Fri, Nov 08, 2019 at 11:40:53AM -0800, Rob Clark wrote:
> > > On Fri, Nov 8, 2019 at 10:42 AM Stephen Boyd <sboyd@kernel.org> wrote:
> > > >
> > > > Quoting Rob Clark (2019-11-08 08:54:23)
> > > > > On Thu, Nov 7, 2019 at 10:35 PM Stephen Boyd <sboyd@kernel.org> wrote:
> > > > > >
> > > > > > Quoting Rob Clark (2019-11-07 18:06:19)
> > > > > > > On Thu, Nov 7, 2019 at 1:06 PM Stephen Boyd <sboyd@kernel.org> wrote:
> > > > > > > >
> > > > > > > >
> > > > > > > > NULL is a valid clk pointer returned by clk_get(). What is the display
> > > > > > > > driver doing that makes it consider NULL an error?
> > > > > > > >
> > > > > > >
> > > > > > > do we not have an iface clk? I think the driver assumes we should
> > > > > > > have one, rather than it being an optional thing.. we could ofc change
> > > > > > > that
> > > > > >
> > > > > > I think some sort of AHB clk is always enabled so the plan is to just
> > > > > > hand back NULL to the caller when they call clk_get() on it and nobody
> > > > > > should be the wiser when calling clk APIs with a NULL iface clk. The
> > > > > > common clk APIs typically just return 0 and move along. Of course, we'll
> > > > > > also turn the clk on in the clk driver so that hardware can function
> > > > > > properly, but we don't need to expose it as a clk object and all that
> > > > > > stuff if we're literally just slamming a bit somewhere and never looking
> > > > > > back.
> > > > > >
> > > > > > But it sounds like we can't return NULL for this clk for some reason? I
> > > > > > haven't tried to track it down yet but I think Matthias has found it
> > > > > > causes some sort of problem in the display driver.
> > > > > >
> > > > >
> > > > > ok, I guess we can change the dpu code to allow NULL.. but what would
> > > > > the return be, for example on a different SoC where we do have an
> > > > > iface clk, but the clk driver isn't enabled? Would that also return
> > > > > NULL? I guess it would be nice to differentiate between those cases..
> > > > >
> > > >
> > > > So the scenario is DT describes the clk
> > > >
> > > > dpu_node {
> > > > clocks = <&cc AHB_CLK>;
> > > > clock-names = "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().
> > > >
> > >
> > > 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.
> > >
> > > From a quick look, I think something like the attached (untested).
> >
> > The driver appears to be happy with it, at least at probe() time.
>
> Ok, I suppose I should re-send the dpu patch to the appropriate
> lists.. does that count as a Tested-by?
Ack
next prev parent reply other threads:[~2019-11-14 17:04 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-14 10:23 [PATCH v4 0/5] Add Global Clock controller (GCC) driver for SC7180 Taniya Das
2019-10-14 10:23 ` [PATCH v4 1/5] clk: qcom: rcg: update the DFS macro for RCG Taniya Das
2019-11-07 21:11 ` Stephen Boyd
2019-10-14 10:23 ` [PATCH v4 2/5] clk: qcom: common: Return NULL from clk_hw OF provider Taniya Das
2019-11-07 21:11 ` Stephen Boyd
2019-10-14 10:23 ` [PATCH v4 3/5] dt-bindings: clock: Add YAML schemas for the QCOM GCC clock bindings Taniya Das
2019-10-14 16:49 ` Rob Herring
2019-11-07 21:11 ` Stephen Boyd
2019-10-14 10:23 ` [PATCH v4 4/5] dt-bindings: clock: Introduce " Taniya Das
2019-10-14 16:50 ` Rob Herring
2019-11-07 21:11 ` Stephen Boyd
2019-10-14 10:23 ` [PATCH v4 5/5] clk: qcom: Add Global Clock controller (GCC) driver for SC7180 Taniya Das
2019-10-29 17:59 ` Matthias Kaehlcke
2019-10-31 11:29 ` Taniya Das
2019-10-31 17:41 ` Matthias Kaehlcke
2019-11-07 21:06 ` Stephen Boyd
2019-11-08 2:06 ` Rob Clark
2019-11-08 6:35 ` Stephen Boyd
2019-11-08 16:54 ` Rob Clark
2019-11-08 18:42 ` Stephen Boyd
2019-11-08 19:40 ` Rob Clark
2019-11-08 21:14 ` Stephen Boyd
2019-11-14 1:02 ` Matthias Kaehlcke
2019-11-14 5:30 ` Rob Clark
2019-11-14 17:04 ` Matthias Kaehlcke [this message]
2019-11-07 21:12 ` Stephen Boyd
2019-11-14 17:34 ` Matthias Kaehlcke
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