linux-kernel - Re: [PATCH 2/9] clk: Introduce get_parent

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Message-ID: <41f8f325-2738-3995-1fc8-354a9412041e@codeaurora.org>
Date:   Mon, 11 Feb 2019 09:09:00 -0700
From:   Jeffrey Hugo <jhugo@...eaurora.org>
To:     Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>
Cc:     linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH 2/9] clk: Introduce get_parent_hw clk op

On 1/28/2019 11:10 PM, Stephen Boyd wrote:
> The clk_ops::get_parent function is limited in ability to return errors
> because it returns a u8. A "workaround" to return an error is to return
> a number >= the number of parents of a clk. This will in turn cause the
> framework to "orphan" the clk and make the parent of the clk NULL. This
> isn't really correct, because if an error occurs while reading the
> parents of a clk we should fail the clk registration, instead of
> orphaning the clk and waiting for the clk to appear later.
> 
> We really need to have three different return values from the get_parent
> clk op. Something valid for a clk that exists, something invalid for a
> clk that doesn't exist and never will exist or can't be determined
> because the register operation to read the parent failed, and something
> for a clk that doesn't exist because the framework doesn't know about
> what it is. Introduce a new clk_op that can express all of this by
> returning a pointer to the clk_hw of the parent. It's expected that clk
> provider drivers will return a valid pointer when the parent is
> findable, an error pointer like EPROBE_DEFER if their parent provider
> hasn't probed yet but is valid, a NULL pointer if they can't find the
> clk but index is valid, and an error pointer with an appropriate error
> code otherwise.
> 
> Cc: Miquel Raynal <miquel.raynal@...tlin.com>
> Cc: Jerome Brunet <jbrunet@...libre.com>
> Cc: Russell King <linux@...linux.org.uk>
> Cc: Michael Turquette <mturquette@...libre.com>
> Signed-off-by: Stephen Boyd <sboyd@...nel.org>

<snip>

> +static int clk_init_parent(struct clk_core *core)
> +{
> +	core->parent = __clk_init_parent(core, true);
> +	if (IS_ERR(core->parent))
> +		return PTR_ERR(core->parent);
> +
> +	/*
> +	 * Populate core->parent if parent has already been clk_core_init'd. If
> +	 * parent has not yet been clk_core_init'd then place clk in the orphan
> +	 * list.  If clk doesn't have any parents then place it in the root
> +	 * clk list.
> +	 *
> +	 * Every time a new clk is clk_init'd then we walk the list of orphan
> +	 * clocks and re-parent any that are children of the clock currently
> +	 * being clk_init'd.
> +	 */
> +	if (core->parent) {
> +		hlist_add_head(&core->child_node,
> +				&core->parent->children);
> +		core->orphan = core->parent->orphan;
> +	} else if (!core->num_parents) {
> +		hlist_add_head(&core->child_node, &clk_root_list);
> +		core->orphan = false;
> +	} else {
> +		hlist_add_head(&core->child_node, &clk_orphan_list);

Missing "core->orphan = true;"?
The snippet below had that line.  Its not clear why it appears to be 
dropped here.

> +	}
> +
> +	return 0;
> +}

<snip>

> @@ -3073,29 +3143,9 @@ static int __clk_core_init(struct clk_core *core)
>   				"%s: invalid NULL in %s's .parent_names\n",
>   				__func__, core->name);
>   
> -	core->parent = __clk_init_parent(core);
> -
> -	/*
> -	 * Populate core->parent if parent has already been clk_core_init'd. If
> -	 * parent has not yet been clk_core_init'd then place clk in the orphan
> -	 * list.  If clk doesn't have any parents then place it in the root
> -	 * clk list.
> -	 *
> -	 * Every time a new clk is clk_init'd then we walk the list of orphan
> -	 * clocks and re-parent any that are children of the clock currently
> -	 * being clk_init'd.
> -	 */
> -	if (core->parent) {
> -		hlist_add_head(&core->child_node,
> -				&core->parent->children);
> -		core->orphan = core->parent->orphan;
> -	} else if (!core->num_parents) {
> -		hlist_add_head(&core->child_node, &clk_root_list);
> -		core->orphan = false;
> -	} else {
> -		hlist_add_head(&core->child_node, &clk_orphan_list);
> -		core->orphan = true;
> -	}
> +	ret = clk_init_parent(core);
> +	if (ret)
> +		goto out;
>   
>   	/*
>   	 * optional platform-specific magic


-- 
Jeffrey Hugo
Qualcomm Datacenter Technologies as an affiliate of Qualcomm 
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.