linux-kernel - Re: [PATCH] clk: check for disabled clock-provider in of_clk_get_hw_from

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Message-ID: <yd2vhz2rivseulpbw34vhyei5sojz5w7ltnzwgtfn3ywwldgu6@nhktt6iztd4r>
Date: Fri, 21 Feb 2025 02:41:40 +0100
From: Sebastian Reichel <sebastian.reichel@...labora.com>
To: Heiko Stuebner <heiko@...ech.de>
Cc: mturquette@...libre.com, sboyd@...nel.org, linux-clk@...r.kernel.org, 
	linux-kernel@...r.kernel.org, liujianfeng1994@...il.com, cristian.ciocaltea@...labora.com
Subject: Re: [PATCH] clk: check for disabled clock-provider in
 of_clk_get_hw_from_clkspec

Hi,

On Thu, Feb 20, 2025 at 11:54:48PM +0100, Heiko Stuebner wrote:
> of_clk_get_hw_from_clkspec checks all available clock-providers by
> compairing their of-nodes to the one from the clkspec. If no matching
> clock-provider is found, the function returns EPROBE_DEFER to cause a
> re-check at a later date.
> 
> If a matching clock-provider is found, a authoritative answer can be
> retrieved from it whether the clock exists or not.
> 
> This does not take into account that the clock-provider may never appear,
> because it's node is disabled. This can happen for example when a clock
> is optional, provided by a separate block which just never gets enabled.
> 
> One example of this happening is the rk3588's VOP, which has optional
> additional display-clock-supplies coming from PLLs inside the hdmiphy
> blocks. These can be used for better rates, but the system will also
> work without them.
> 
> The problem around that is described in the followups to:
> https://lore.kernel.org/dri-devel/20250215-vop2-hdmi1-disp-modes-v1-3-81962a7151d6@collabora.com/
> 
> As we already know the of-node of the presumed clock-provider, just add
> a check via of_device_is_available whether this is a "valid" device node.
> This prevents ethernal defer-loops.

if there is a respin:

s/ethernal/eternal

> Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> ---

Also seems useful for having a quick final error if a referenced
clock node has not been enabled by accident during board bringup.

Reviewed-by: Sebastian Reichel <sebastian.reichel@...labora.com>

Thanks,

-- Sebastian

>  drivers/clk/clk.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index cf7720b9172f..50faafbf5dda 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -5258,6 +5258,10 @@ of_clk_get_hw_from_clkspec(struct of_phandle_args *clkspec)
>  	if (!clkspec)
>  		return ERR_PTR(-EINVAL);
>  
> +	/* Check if node in clkspec is in disabled/fail state */
> +	if (!of_device_is_available(clkspec->np))
> +		return ERR_PTR(-ENOENT);
> +
>  	mutex_lock(&of_clk_mutex);
>  	list_for_each_entry(provider, &of_clk_providers, link) {
>  		if (provider->node == clkspec->np) {
> -- 
> 2.47.2
> 

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