[PATCH v2] clk: fixed-rate: Use "clock-output-names" to name fixed clocks

[Adam Ford]

On Sat, Apr 19, 2025 at 2:12 PM Fabio Estevam <festevam at gmail.com> wrote:
>
> Hi Marek,
>
> On Fri, Apr 18, 2025 at 11:53 AM Marek Vasut <marex at denx.de> wrote:
>
> > The "clock-output-names" is NEVER used for any clock look up.
>
> In Linux, "clock-output-names" is used to register the name of the
> fixed-rate clock.
>
> From Linux drivers/clk/clk-fixed-rate.c:
>
> ```
> static struct clk_hw *_of_fixed_clk_setup(struct device_node *node)
> {
> ....
>
> of_property_read_string(node, "clock-output-names", &clk_name);
>
> hw = clk_hw_register_fixed_rate_with_accuracy(NULL, clk_name, NULL,
>     0, rate, accuracy);
> ```
>
> In U-Boot, we should register a fixed-rate clock with the same name as in Linux.
>
> This patch aims to make the U-Boot fixed-rate clock name conform to
> Linux standards.
>
> > I am fine with the first half of the description, but the second half is
> > wrong and this actually does not fix anything. Simply remove
> > clock-output-names from the osc_24m and the code will be broken again.
>
> In Linux, if "clock-output-names" is removed from the osc_24m node,
> the console becomes corrupted
> on an imx8mp-evk.
>
> > The clk_resolve_parent_clk() is meant to perform the aforementioned
> > resolution(), that is what "[PATCH v2 00/24] clk: Add
> > clk_resolve_parent_clk() and fix up iMX clock drivers" actually fixed.
> > It seems there is something still missing and clk_resolve_parent_clk()
> > does not do the resolution properly for some clock, but that is what
> > needs to be understood and fixed, not worked around this way.
>
> Please try to reproduce the problem on your end.
>
> On an imx8mp-based board, run 'usb start' in U-Boot, and this command will fail.

>From what I can tell, on the imx8mp, the usb_phy_ref parent->dev->name
value s "clock-osc-24m" which never matches "osc_24" and I put some
debug code into clk_mux_fetch_parent_index.

I think clk_mux_fetch_parent_index needs some additional logic to go
up the chain to the root node and look for 'clock-names' to match in
addition to what it already does. I am just not sure of the best
method to go up the tree to find the root node that defines it.

adam

>
> Thanks