[PATCH RFC 0/3] clk: support arbitrary clk_register() sequence

[Simon Glass]

Hi Yang,

On Tue, 14 Oct 2025 at 23:03, Tom Rini <trini at konsulko.com> wrote:
>
> On Sat, Jun 21, 2025 at 06:54:17PM +0800, Yang Xiwen wrote:
>
> > Currently U-Boot clk framework mandates the sequence of registering clks
> > to begin from root, and then its children. This is an addtional
> > requirement that doesn't exist in Linux kernel, which makes clk driver
> > porting more difficult.
> >
> > Let's handle this entirely in clk framework and give driver the freedom
> > to register clocks in any order.
> >
> > This is done by assigning the parent "lazily". It will cache the parent
> > name in the core clk struct and try to refresh it when clk consumers
> > call clk_get_parent(). It's transparent to clk consumers as long as they
> > only use APIs provided by clk framework.
> >
> > I've ran `ut dm clk*` and verified these commits does not break any
> > existing testcases. Though no new testcase is added because I think
> > existing testcases already test the logic very well.
>
> Sorry for the very late review. When I build this on say
> rock-4c-plus-rk3399 this is the size growth I see:
>             rock-4c-plus-rk3399: all +228 spl/u-boot-spl:all +500 spl/u-boot-spl:text +500 text +228 tpl/u-boot-tpl:all +552 tpl/u-boot-tpl:text +552
>                u-boot: add: 1/0, grow: 1/0 bytes: 228/0 (228)
>                  function                                   old     new   delta
>                  device_reparent                              -     120    +120
>                  clk_get_parent                              56     164    +108
>                spl-u-boot-spl: add: 4/0, grow: 1/0 bytes: 500/0 (500)
>                  function                                   old     new   delta
>                  uclass_find_device_by_namelen                -     172    +172
>                  device_reparent                              -     120    +120
>                  clk_get_parent                              56     144     +88
>                  uclass_find_device_by_name                   -      68     +68
>                  uclass_get_device_by_name                    -      52     +52
>                tpl-u-boot-tpl: add: 5/0, grow: 1/0 bytes: 552/0 (552)
>                  function                                   old     new   delta
>                  uclass_find_device_by_namelen                -     172    +172
>                  device_reparent                              -     120    +120
>                  clk_get_parent                              56     144     +88
>                  uclass_find_device_by_name                   -      68     +68
>                  uclass_get_device_by_name                    -      52     +52
>                  strncmp                                      -      52     +52
>
> (using buildman's 'bloat' features to report size change). I'm fine with
> the growth in U-Boot itself, but that's just too much in SPL and TPL and
> we need to figure out if we can avoid that somehow.

You could add a Kconfig for this option, like CLK_LAZY_PARENT and then
use CONFIG_IS_ENABLED() so it is separately enabled in SPL, and
default off.

Also please add a test case to test/dm/clk.c (or clk_ccf.c) that
covers your changes.

Regards,
Simon