Re: [PATCH v2 1/2] clk: Warn and add workaround on misuse of .parent_data with .name only

Christian Marangi
2023-02-15T23:42:27Z

On Wed, Feb 15, 2023 at 10:54:56AM -0800, Stephen Boyd wrote:
> Quoting Christian Marangi (2023-02-10 10:34:11)
> > On Fri, Feb 10, 2023 at 04:40:29PM -0800, Stephen Boyd wrote:
> > > Quoting Christian Marangi (2023-01-31 08:08:28)
> > > > By a simple mistake in a .parent_names to .parent_data conversion it was
> > > > found that clk core assume fw_name is always provided with a parent_data
> > > > struct for each parent and never fallback to .name to get parent name even
> > > > if declared.
> > >
> > > It sounds like you have clk_parent_data and the .index member is 0? Can
> > > you show an example structure? I'm guessing it is like this:
> > >
> > > struct clk_parent_data pdata = { .name = "global_name" };
> > >
> >
> > An example of this problem and the relative fix is here
> > 35dc8e101a8e08f69f4725839b98ec0f11a8e2d3
> >
> > You example is also ok and this patch wants to handle just a case like
> > that.
>
> Ok, so you have a firmware .index of 0. The .name is a fallback. I
> suppose you want the .name to be a fallback if there isn't a clocks
> property in the registering device node? I thought that should already
> work but maybe there is a bug somewhere. Presumably you have a gcc node
> that doesn't have a clocks property
>
> gcc: gcc@1800000 {
> compatible = "qcom,gcc-ipq8074";
> reg = <0x01800000 0x80000>;
> #clock-cells = <0x1>;
> #power-domain-cells = <1>;
> #reset-cells = <0x1>;
> };
>
> Looking at clk_core_get() we'll call of_parse_clkspec() and that should fail
>
> struct clk_hw *hw = ERR_PTR(-ENOENT);
>
> ...
>
> if (np && (name || index >= 0) &&
> !of_parse_clkspec(np, index, name, &clkspec)) {
> ...
> } else if (name) {
> ...
> }
>
> if (IS_ERR(hw))
> return ERR_CAST(hw);
>
> so we should have a -ENOENT clk_hw pointer in
> clk_core_fill_parent_index(). That should land in this if condition in
> clk_core_fill_parent_index()
>
> parent = clk_core_get(core, index);
> if (PTR_ERR(parent) == -ENOENT && entry->name)
> parent = clk_core_lookup(entry->name);
>
> and then entry->name should be used.
>

Hi, thanks for making me give this an extra check... I think I found
the real cause.
I send a patch that should suppress this and give an extensive
explaination of the problem.
This is the ID: 20230215232712.17072-1-ansuelsmth@gmail.com

The hint that made me get what was wrong was a problem with index and
the fact that it should have returned -ENOENT... Fun to discover a clock
was actually returned and the function never returned an error.

> >
> > > >
> > > > This is caused by clk_core_get that only checks for parent .fw_name and
> > > > doesn't handle .name.
> > >
> > > clk_core_get() is not supposed to operate on the .name member. It is a
> > > firmware based lookup with clkdev as a fallback because clkdev is a
> > > psudeo-firmware interface to assign a name to a clk when some device
> > > pointer is used in conjunction with it.
> > >
> >
> > And the problem is just that. We currently permit to have a
> > configuration with .name but no .fw_name. In a case like that a dev may
> > think that this configuration is valid but in reality the clk is
> > silently ignored/not found and cause clk problem with selecting a
> > parent.
>
> It is valid though.
>
> >
> > Took some good hours to discover this and to me it seems an error that
> > everybody can do since nowhere is specificed that the following
> > parent_data configuration is illegal.
> >
>
> I'll look at adding a test. Seems to be the best way to solve this.

Eh probably a test may have made this more clear. The main problem here
was that the function never returned an error but under the hood the
parent was pointing to another clock.

--
Ansuel