linux-kernel - Re: [PATCH] clk: composite: Also consider .determine

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Message-ID: <163433322577.1688384.5988903670868801272@swboyd.mtv.corp.google.com>
Date:   Fri, 15 Oct 2021 14:27:05 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     heiko@...ech.de, knaerzche@...il.com,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        martin.blumenstingl@...glemail.com
Subject: Re: [PATCH] clk: composite: Also consider .determine_rate for rate + mux composites

Quoting Martin Blumenstingl (2021-10-15 05:05:59)
> Commit 69a00fb3d69706 ("clk: divider: Implement and wire up
> .determine_rate by default") switches clk_divider_ops to implement
> .determine_rate by default. This breaks composite clocks with multiple
> parents because clk-composite.c does not use the special handling for
> mux + divider combinations anymore (that was restricted to rate clocks
> which only implement .round_rate, but not .determine_rate).
> 
> Alex reports:
>   This breaks lot of clocks for Rockchip which intensively uses
>   composites,  i.e. those clocks will always stay at the initial parent,
>   which in some cases  is the XTAL clock and I strongly guess it is the
>   same for other platforms,  which use composite clocks having more than
>   one parent (e.g. mediatek, ti ...)
> 
>   Example (RK3399)
>   clk_sdio is set (initialized) with XTAL (24 MHz) as parent in u-boot.
>   It will always stay at this parent, even if the mmc driver sets a rate
>   of  200 MHz (fails, as the nature of things), which should switch it
>   to   any of its possible parent PLLs defined in
>   mux_pll_src_cpll_gpll_npll_ppll_upll_24m_p (see clk-rk3399.c)  - which
>   never happens.
> 
> Restore the original behavior by changing the priority of the conditions
> inside clk-composite.c. Now the special rate + mux case (with rate_ops
> having a .round_rate - which is still the case for the default
> clk_divider_ops) is preferred over rate_ops which have .determine_rate
> defined (and not further considering the mux).
> 
> Fixes: 69a00fb3d69706 ("clk: divider: Implement and wire up .determine_rate by default")
> Reported-by: Alex Bee <knaerzche@...il.com>
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
> ---
> Re-sending this as inline patch instead of attaching it.
> 
>  drivers/clk/clk-composite.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/clk/clk-composite.c b/drivers/clk/clk-composite.c
> index 0506046a5f4b..510a9965633b 100644
> --- a/drivers/clk/clk-composite.c
> +++ b/drivers/clk/clk-composite.c
> @@ -58,11 +58,8 @@ static int clk_composite_determine_rate(struct clk_hw *hw,
>         long rate;
>         int i;
>  
> -       if (rate_hw && rate_ops && rate_ops->determine_rate) {
> -               __clk_hw_set_clk(rate_hw, hw);
> -               return rate_ops->determine_rate(rate_hw, req);
> -       } else if (rate_hw && rate_ops && rate_ops->round_rate &&
> -                  mux_hw && mux_ops && mux_ops->set_parent) {
> +       if (rate_hw && rate_ops && rate_ops->round_rate &&
> +           mux_hw && mux_ops && mux_ops->set_parent) {

What do we do if rate_ops and mux_ops only implement determine_rate? It
will fail right? We can't mesh them together in function. We should
probably fail to let the composite clk be registered if that happens.

>                 req->best_parent_hw = NULL;
>  
>                 if (clk_hw_get_flags(hw) & CLK_SET_RATE_NO_REPARENT) {
> @@ -107,6 +104,9 @@ static int clk_composite_determine_rate(struct clk_hw *hw,
>  
>                 req->rate = best_rate;
>                 return 0;
> +       } else if (rate_hw && rate_ops && rate_ops->determine_rate) {
> +               __clk_hw_set_clk(rate_hw, hw);
> +               return rate_ops->determine_rate(rate_hw, req);
>         } else if (mux_hw && mux_ops && mux_ops->determine_rate) {
>                 __clk_hw_set_clk(mux_hw, hw);
>                 return mux_ops->determine_rate(mux_hw, req);
> -- 
> 2.33.0
>