linux-kernel - Re: [PATCH v5 4/4] clk: eyeq: add driver

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Message-ID: <39b99c310a307d97955ec6f9335c0439.sboyd@kernel.org>
Date: Mon, 28 Oct 2024 15:52:41 -0700
From: Stephen Boyd <sboyd@...nel.org>
To: Conor Dooley <conor+dt@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Michael Turquette <mturquette@...libre.com>, Rob Herring <robh@...nel.org>, Théo Lebrun <theo.lebrun@...tlin.com>
Cc: devicetree@...r.kernel.org, linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org, Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>, Grégory Clement <gregory.clement@...tlin.com>, Thomas Petazzoni <thomas.petazzoni@...tlin.com>, Tawfik Bayouk <tawfik.bayouk@...ileye.com>
Subject: Re: [PATCH v5 4/4] clk: eyeq: add driver

Quoting Théo Lebrun (2024-10-24 05:50:16)
> The bug is elsewhere: we do get valid clocks from PL011. Both clk_get()
> calls give proper pointers.
> 
> The issue is that we are using `compatible = "fixed-factor-clock"`
> clocks in the middle, and those don't wait for their parents to be
> active.
> 
> Simplified clock graph is: pll-per -> occ-periph.
> pll-per is register by our driver. occ-periph looks like:
> 
>         occ_periph: occ-periph {
>                 compatible = "fixed-factor-clock";
>                 clocks = <&olb EQ5C_PLL_PER>;
>                 #clock-cells = <0>;
>                 clock-div = <16>;
>                 clock-mult = <1>;
>         };

Why is this fixed factor clk registered from DT vs. from the driver that
registers pll-per? Is it useful to describe it in DT because the factor
can change? Where does it physically exist? In the SoC?

> 
> Sequence is:
>  - eqc_early_init(): it registers a clock provider that will return
>    EPROBE_DEFER for our pll-per.
>  - _of_fixed_factor_clk_setup(): it registers occ-periph, even though
>    its parent is EPROBE_DEFER. clk_core_populate_parent_map() runs all
>    fine without complaining; logical as it doesn't query the clk_hw for
>    its parent, it only stores indexes.
>  - amba_get_enable_pclk(): it does a clk_get() which works because
>    occ-periph exists.
> 
> Maybe __clk_register() should check the clk_hw for each parent: if any
> is an EPROBE_DEFER then it should EPROBE_DEFER itself? That looks like
> a rather big behavioral change.
> 
> The other solution is to keep as-is: provide all clocks consumed by
> fixed-factor-clocks at of_clk_init() stage.

Another solution is to register the fixed factor clk from the pll-per
clk provider.

And yet another solution is to return EPROBE_DEFER for orphaned clks. We
have everything in place for that but we ran into trouble with consumers
wanting to get orphaned clks in their probe or during assigned-clocks
handling.