linux-kernel - Re: [PATCH] of: property: do not create clocks device link for clock controllers

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Date:   Mon, 29 Nov 2021 15:52:25 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH] of: property: do not create clocks device link for clock controllers

On Mon, Nov 29, 2021 at 3:48 PM Saravana Kannan <saravanak@...gle.com> wrote:
>
> On Thu, Nov 25, 2021 at 10:36 AM Dmitry Baryshkov
> <dmitry.baryshkov@...aro.org> wrote:
> >
> > Do not create device link for clock controllers.
>
> Nak.
>
> > Some of the clocks
> > provided to the device via OF can be the clocks that are just parents to
> > the clocks provided by this clock controller. Clock subsystem already
> > has support for handling missing clock parents correctly (clock
> > orphans). Later when the parent clock is registered, clocks get
> > populated properly.
> >
> > An example of the system where this matters is the SDM8450 MTP board
> > (see arch/arm64/boot/dts/qcom/sdm845-mtp.dts). Here the dispcc uses
> > clocks provided by dsi0_phy and dsi1_phy device tree nodes. However the
> > dispcc itself provides clocks to both PHYs, to the PHY parent device,
> > etc. With just dsi0_phy in place devlink is able to break the
> > dependency,
>
> Right, because I wrote code to make sure we handle these clock
> controller cases properly. If that logic isn't smart enough, let's fix
> that.
>
> > but with two PHYs, dispcc doesn't get probed at all, thus
> > breaking display support.
>
> Then let's find out why and fix this instead of hiding some
> dependencies from fw_devlink. You could be breaking other cases/boards
> with this change you are making.

Btw, forgot to mention. I'll look into this one and try to find the
reason why it wasn't handled automatically. And then come up with a
fix.

If you want to find out why fw_devlink didn't notice the cycle
correctly for the case of 2 PHYs vs 1 PHY, I'd appreciate that too.

Btw, same comment for remote-endpoint. I'll look into what's going on
in that case. Btw, I'm assuming all the code and DT you are testing
this on is already upstream. Can you please confirm that?

-Saravana

>
> -Saravana
>
> > Cc: Bjorn Andersson <bjorn.andersson@...aro.org>
> > Cc: Stephen Boyd <swboyd@...omium.org>
> > Cc: Saravana Kannan <saravanak@...gle.com>
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > ---
> >  drivers/of/property.c | 16 +++++++++++++++-
> >  1 file changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/of/property.c b/drivers/of/property.c
> > index a3483484a5a2..f7229e4030e3 100644
> > --- a/drivers/of/property.c
> > +++ b/drivers/of/property.c
> > @@ -1264,7 +1264,6 @@ struct supplier_bindings {
> >         bool node_not_dev;
> >  };
> >
> > -DEFINE_SIMPLE_PROP(clocks, "clocks", "#clock-cells")
> >  DEFINE_SIMPLE_PROP(interconnects, "interconnects", "#interconnect-cells")
> >  DEFINE_SIMPLE_PROP(iommus, "iommus", "#iommu-cells")
> >  DEFINE_SIMPLE_PROP(mboxes, "mboxes", "#mbox-cells")
> > @@ -1294,6 +1293,21 @@ DEFINE_SIMPLE_PROP(backlight, "backlight", NULL)
> >  DEFINE_SUFFIX_PROP(regulators, "-supply", NULL)
> >  DEFINE_SUFFIX_PROP(gpio, "-gpio", "#gpio-cells")
> >
> > +static struct device_node *parse_clocks(struct device_node *np,
> > +                                       const char *prop_name, int index)
> > +{
> > +       /*
> > +        * Do not create clock-related device links for clocks controllers,
> > +        * clock orphans will handle missing clock parents automatically.
> > +        */
> > +       if (!strcmp(prop_name, "clocks") &&
> > +           of_find_property(np, "#clock-cells", NULL))
> > +               return NULL;
> > +
> > +       return parse_prop_cells(np, prop_name, index, "clocks",
> > +                                      "#clock-cells");
> > +}
> > +
> >  static struct device_node *parse_gpios(struct device_node *np,
> >                                        const char *prop_name, int index)
> >  {
> > --
> > 2.33.0
> >