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

[Jerome Brunet]

On mar. 21 juil. 2026 at 18:48, Brian Masney <bmasney@xxxxxxxxxx> wrote:

> Hi Jerome,
>
> On Tue, Jul 21, 2026 at 12:08:17PM +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@xxxxxxxxxxxx>
>> ---
>> 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
>> """
>> 
>> I initially thought about using the dev parameter and compare it
>> against the clock own device but this proved unreliable. A clock
>> does not always have a backing device and some paths, such as
>> clk_get_sys(), do not provide a device either.
>> 
>> 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.
>
> __clk_register() has this comment:
>
>         /*
>          * Don't call clk_hw_create_clk() here because that would pin the
>          * provider module to itself and prevent it from ever being removed.
>          */
>         hw->clk = alloc_clk(core, NULL, NULL);
>
> With your change, can this code path be updated to use clk_hw_create_clk() ?
>

Indeed the comment no longer applies but I think keeping alloc
here is best. It avoids "linking a consumer" here where there should not
be one. All clocks would appear to have consumer in the clk summary, it
would weird. 

The end goal is remove the hw->clk. I've restarted the work to rid the
kernel of using this. Some rework don't need clk_hw_create_clk() and are
not blocked by this patch but most will.

Once this is done, we could probably merge clk_hw_create_clk() and
alloc(), the split won't have purpose anymore.

> Brian

-- 
Jerome