Re: [PATCH 22/22] clk: Prevent a clock without a rate to register

[Stephen Boyd <sboyd@kernel.org>]

Quoting Maxime Ripard (2022-04-08 02:10:37)
> A rate of 0 for a clock is considered an error, as evidenced by the
> documentation of clk_get_rate() and the code of clk_get_rate() and
> clk_core_get_rate_nolock().
> 
> The main source of that error is if the clock is supposed to have a
> parent but is orphan at the moment of the call. This is likely to be
> transient and solved later in the life of the system as more clocks are
> registered.
> 
> The corollary is thus that if a clock is not an orphan, has a parent that
> has a rate (so is not an orphan itself either) but returns a rate of 0,
> something is wrong in the driver. Let's return an error in such a case.
> 
> Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> ---
>  drivers/clk/clk.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 8bbb6adeeead..e8c55678da85 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -3773,6 +3773,16 @@ static int __clk_core_init(struct clk_core *core)
>                 rate = 0;
>         core->rate = core->req_rate = rate;
>  
> +       /*
> +        * If we're not an orphan clock and our parent has a rate, then
> +        * if our rate is 0, something is badly broken in recalc_rate.
> +        */
> +       if (!core->orphan && (parent && parent->rate) && !core->rate) {

It's possible that it is an orphan at time of registration, so this
check doesn't even cover the case when it is parented by a later clk
registration. How would we error out when parenting the clk to the
parent if recalc_rate then starts returning 0? It doesn't seem possible
to implement this.