Date:   Fri, 6 Jul 2018 11:47:41 -0600
From:   Rob Herring <robh@...nel.org>
To:     Amit Kucheria <amit.kucheria@...aro.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Eduardo Valentin <edubezval@...il.com>,
        Siddartha Mohanadoss <smohanad@...eaurora.org>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Andy Gross <andy.gross@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v4 4/6] thermal: tsens: Add support for SDM845

On Thu, Jul 5, 2018 at 11:13 PM Amit Kucheria <amit.kucheria@...aro.org> wrote:
>
> On Fri, Jul 6, 2018 at 2:07 AM Rob Herring <robh@...nel.org> wrote:
> >
> > On Wed, Jul 04, 2018 at 10:56:26PM +0530, Amit Kucheria wrote:
> > > On Tue, Jul 3, 2018 at 9:56 PM, Rob Herring <robh@...nel.org> wrote:
> > > > On Mon, Jul 02, 2018 at 06:14:07PM +0530, Amit Kucheria wrote:
> > > >> SDM845 uses v2.4.0 of the TSENS IP block but the get_temp() function
> > > >> appears to be identical across v2.x.y in code seen so far. We use the
> > > >> generic get_temp() function.
> > > >>
> > > >> Signed-off-by: Amit Kucheria <amit.kucheria@...aro.org>
> > > >> ---
> > > >>  Documentation/devicetree/bindings/thermal/qcom-tsens.txt | 2 ++
> > > >>  drivers/thermal/qcom/tsens-v2.c                          | 6 +++++-
> > > >>  drivers/thermal/qcom/tsens.c                             | 6 ++++++
> > > >>  drivers/thermal/qcom/tsens.h                             | 5 ++++-
> > > >>  4 files changed, 17 insertions(+), 2 deletions(-)
> > > >>
> > > >> diff --git a/Documentation/devicetree/bindings/thermal/qcom-tsens.txt b/Documentation/devicetree/bindings/thermal/qcom-tsens.txt
> > > >> index 06195e8..075182e 100644
> > > >> --- a/Documentation/devicetree/bindings/thermal/qcom-tsens.txt
> > > >> +++ b/Documentation/devicetree/bindings/thermal/qcom-tsens.txt
> > > >> @@ -5,6 +5,8 @@ Required properties:
> > > >>   - "qcom,msm8916-tsens" : For 8916 Family of SoCs
> > > >>   - "qcom,msm8974-tsens" : For 8974 Family of SoCs
> > > >>   - "qcom,msm8996-tsens" : For 8996 Family of SoCs
> > > >> + - "qcom,tsens-v2.4.0"  : For SDM845 Family of SoCs
> > > >> + - "qcom,tsens-v2"      : Generic fallback binding for any Soc using 2.x.y version of the tsens IP
> > > >
> > > > You need to show what are valid combinations of compatibles. Does v2
> > > > apply to 8996? One valid combination per line.
> > >
> > > I've restructured qcom-tsens.txt to look like this:
> > >
> > > -----%<-------
> > >
> > > * QCOM SoC Temperature Sensor (TSENS)
> > >
> > > Required properties:
> > > - compatible: must be one of the following:
> > >     - "qcom,msm8916-tsens" (MSM8916)
> > >     - "qcom,msm8974-tsens" (MSM8974)
> > >     - "qcom,msm8996-tsens" (MSM8996)
> > >     - "qcom,tsens-<ip_version>", "qcom,tsens-v2" (TSENS IP version and a
> > >        generic v2 property as fallback except for MSM8996)
> > >
> > >   Examples with ip_version are:
> > >     - "qcom,tsens-v2.4.0", "qcom,tsens-v2" (SDM845)
> > >     - "qcom,tsens-v2.2.1", "qcom,tsens-v2" (MSM8998)
> > >
> > > -----%<-------
> > >
> > > 8996 would end up being something like this if needed, though we're
> > > stuck with "qcom,msm8996-tsens":
> > > "qcom,msm8996-tsens", "qcom,tsens-v2.1.0", "qcom,tsens-v2" (MSM8996)
> >
> > 3 versions here for 3 SoCs. I'm not getting that convinced version
> > numbers really are better. I would assume that other QCom IP blocks
>
> Yeah, it is a bit unfortunate that the 3-4 SoCs we're focusing on
> getting supported upstream have different versions of the TSENS IP.
> The other goal of this work was to make the upstream driver
> feature-complete so we can make a case to switch to it in the
> downstream trees, even on platforms that aren't being active
> upstreamed. They'll still need to keep around those SoC-specific
> one-liner patches in the downstream trees.

Why? They can just use the "v2" fallback (which was sufficient for
your original version). That's not my recommendation, but what do I
care for downstream. Only upstream needs the specific strings to
appease the annoying DT maintainers.

Plus, if it's not upstream, it doesn't exist. :)

> > have versions too, but pretty much *every* *other* binding uses SoC names.
> > Why is this one special?
>
> I'm not an expert on all QC IPs, but this one _seems_ to be reused a
> lot more than others.
>
> > The other problem with versions is the mapping
> > of versions to SoCs most likely can't be validated outside of QCom
> > unless there's a version register.
>
> There is in fact a HW version register that I was hoping to add
> support for later.

Yes, you should rely on that as much as possible. But I have seen h/w
designers forget to update revision registers or there can be
integration differences even if the IP version is the same.

> > So, sorry to go in circles, but can you go back to qcom,<soc>-tsens. You
> > can keep qcom,tsens-v2 as a fallback.
>
> OK.
>
> > Yes, it's annoying to have to update bindings for new SoCs. But it's
> > trivial one line patches. Look at Renesas bindings. Maybe adding new
> > ones will be scriptable once we move to json-schema binding docs.
>
> I did look at the Renesas RCar bindings when restructuring the
> documentation. They seem to have settled upon a 3-level fallback:
> "soc-specific", "generic-no TZ", "generic-TZ". But
> drivers/thermal/rcar_thermal.c seems to be compatible with only one
> soc-specific property (thermal-r8a77995) and all other SoCs seem to be
> just relying the fallbacks.
>
> Anyways, I'll respin.
>
> Thanks.
>
> Regards,
> Amit

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