linux-kernel - Re: [PATCH v2 6/8] clk: Allow parents to be specified without string names

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Date:   Wed, 6 Mar 2019 14:45:38 -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>,
        Chen-Yu Tsai <wens@...e.org>
Subject: Re: [PATCH v2 6/8] clk: Allow parents to be specified without string
 names

On 3/6/2019 10:48 AM, Stephen Boyd wrote:
> Quoting Jeffrey Hugo (2019-03-02 13:25:06)
>> On 2/26/2019 3:34 PM, Stephen Boyd wrote:
>>> The common clk framework is lacking in ability to describe the clk
>>> topology without specifying strings for every possible parent-child
>>> link. There are a few drawbacks to the current approach:
>>>
>>>    1) String comparisons are used for everything, including describing
>>>    topologies that are 'local' to a single clock controller.
>>>
>>>    2) clk providers (e.g. i2c clk drivers) need to create globally unique
>>>    clk names to avoid collisions in the clk namespace, leading to awkward
>>>    name generation code in various clk drivers.
>>>
>>>    3) DT bindings may not fully describe the clk topology and linkages
>>>    between clk controllers because drivers can easily rely on globally unique
>>>    strings to describe connections between clks.
>>>
>>> This leads to confusing DT bindings, complicated clk name generation
>>> code, and inefficient string comparisons during clk registration just so
>>> that the clk framework can detect the topology of the clk tree.
>>> Furthermore, some drivers call clk_get() and then __clk_get_name() to
>>> extract the globally unique clk name just so they can specify the parent
>>> of the clk they're registering. We have of_clk_parent_fill() but that
>>> mostly only works for single clks registered from a DT node, which isn't
>>> the norm. Let's simplify this all by introducing two new ways of
>>> specifying clk parents.
>>>
>>> The first method is an array of pointers to clk_hw structures
>>> corresponding to the parents at that index. This works for clks that are
>>> registered when we have access to all the clk_hw pointers for the
>>> parents.
>>>
>>> The second method is a mix of clk_hw pointers and strings of local and
>>> global parent clk names. If the .name member of the map is set we'll
>>> look for that clk by performing a DT based lookup of the device the clk
>>> is registered with and the .name specified in the map. If that fails,
>>> we'll fallback to the .fallback member and perform a global clk name
>>> lookup like we've always done before.
>>>
>>> Using either one of these new methods is entirely optional. Existing
>>> drivers will continue to work, and they can migrate to this new approach
>>> as they see fit. Eventually, we'll want to get rid of the 'parent_names'
>>> array in struct clk_init_data and use one of these new methods instead.
>>>
>>
>> I don't know exactly what regressed from V1, but this change breaks all
>> clock drivers as far as I can tell.  All clocks from old and new (ie
>> 8998 mmcc rebased onto this) drivers end up as orphans.
>>
>> Is there some data I can provide to help you figure out the issue?
>>
> 
> Can you try this patch? It fixes a pointer blunder that I'm sad about.

That did the trick.  Everything seems to work again.  I haven't 
identified any additional issues.

> 
> ----8<-----
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 37aea7884166..d12afd256dc5 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -3297,15 +3297,17 @@ struct clk *clk_hw_create_clk(struct device *dev, struct clk_hw *hw,
>   	return clk;
>   }
>   
> -static int clk_cpy_name(const char *dst, const char *src, bool must_exist)
> +static int clk_cpy_name(const char **dst_p, const char *src, bool must_exist)
>   {
> +	const char *dst;
> +
>   	if (!src) {
>   		if (must_exist)
>   			return -EINVAL;
>   		return 0;
>   	}
>   
> -	dst = kstrdup_const(src, GFP_KERNEL);
> +	*dst_p = dst = kstrdup_const(src, GFP_KERNEL);
>   	if (!dst)
>   		return -ENOMEM;
>   
> @@ -3341,14 +3343,14 @@ static int clk_core_populate_parent_map(struct clk_core *core)
>   			WARN(!parent_names[i],
>   				"%s: invalid NULL in %s's .parent_names\n",
>   				__func__, core->name);
> -			ret = clk_cpy_name(parent->name, parent_names[i],
> +			ret = clk_cpy_name(&parent->name, parent_names[i],
>   					   true);
>   		} else if (parent_data) {
>   			parent->hw = parent_data[i].hw;
> -			ret = clk_cpy_name(parent->fw_name,
> +			ret = clk_cpy_name(&parent->fw_name,
>   					   parent_data[i].fw_name, false);
>   			if (!ret)
> -				ret = clk_cpy_name(parent->name,
> +				ret = clk_cpy_name(&parent->name,
>   						   parent_data[i].name,
>   						   false);
>   		} else if (parent_hws) {
> 


-- 
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.