Re: [PATCH v2] clk: fix self-consuming provider module pinning

[Brian Masney <bmasney@redhat.com>]

Hi Chen-Yu,

On Thu, Jul 23, 2026 at 03:00:51PM +0200, Jerome Brunet wrote:
> clk_hw_get_clk() lets a provider get a struct clk for one of its own
> struct clk_hw.
> 
> When a struct clk is created, the module usage count of the provider
> is unconditionally increased. For a self-consuming provider, this means
> it pins itself and the module can never be unloaded.
> 
> Increasing the module usage count should only be done when the consumer
> lives in a different module from the provider. Use THIS_MODULE to
> capture caller's module and increase the module usage count accordingly.
> 
> It is OK for consumer-only APIs such as clk_get() or of_clk_get() to
> pass a NULL owner. As a result, any provider module will get pinned,
> same as before.
> 
> Fixes: 30d6f8c15d2c ("clk: add api to get clk consumer from clk_hw")
> Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
> ---
> This issue has been present for a while. Virtually all users of
> clk_hw_get_clk() are affected. The majority are compiled as builtins
> according to the defconfigs. It is not problem in this case but it is
> if the configuration is changed to module.
> 
> The following modules are using clk_hw_get_clk() and are compiled as
> module with some shipped defconfigs:
> * drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_pll.c
> * drivers/phy/cadence/phy-cadence-sierra.c
> * drivers/pwm/pwm-meson.c
> * sound/soc/codecs/lpass-va-macro.c
> 
> Currently those module cannot be unloaded once they have been loaded.
> 
> """
> rmmod: ERROR: Module blabla-module is in use
> """
> 
> With this applied, we can get back to removing the direct usage
> of the struct clk in struct clk_hw and eventually remove this
> struct member entirely.

Do you have any thoughts about this patch to the clk core? I agree with
Stephen that we should add kunit tests for changes to the clk core where
possible, however in this particular case I think it would be very
complicated. It also feels more like an integration test instead of a
unit test to me. In the hopefully limited cases where we don't add kunit
tests, I think it would be good to get multiple trusted contributors to
review.

Thanks,

Brian