linux-kernel - Re: [PATCH v2] clk: ti: dra7-atl: don't allocate `parent

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Message-Id: <20221101183513.C63E4C433C1@smtp.kernel.org>
Date:   Tue, 01 Nov 2022 11:35:11 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Dario Binacchi <dario.binacchi@...rulasolutions.com>
Cc:     linux-kernel@...r.kernel.org,
        Amarula patchwork <linux-amarula@...rulasolutions.com>,
        michael@...rulasolutions.com, kernel test robot <lkp@...el.com>,
        Allison Randal <allison@...utok.net>,
        Miaoqian Lin <linmq006@...il.com>,
        Michael Turquette <mturquette@...libre.com>,
        Tero Kristo <kristo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tony Lindgren <tony@...mide.com>, linux-clk@...r.kernel.org,
        linux-omap@...r.kernel.org
Subject: Re: [PATCH v2] clk: ti: dra7-atl: don't allocate `parent_names' variable

Quoting Dario Binacchi (2022-10-30 06:00:46)
> 
> I tried to test your suggestions on another platform (I don't have the
> hw to test the driver change) but if I
> don't add pdata.name = of_clk_get_parent_name () the board boot up fails.
> 
> As far I can see from the clk_core_populate_parent_map()
> 
> ....
> /* Copy everything over because it might be __initdata */
> for (i = 0, parent = parents; i < num_parents; i++, parent++) {
>     parent->index = -1;
>     if (parent_names) {
>         /* throw a WARN if any entries are NULL */
>        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],
>                                         true);
>     } else if (parent_data) {
>         parent->hw = parent_data[i].hw;
>         parent->index = parent_data[i].index;
>         ret = clk_cpy_name(&parent->fw_name,
>                                          parent_data[i].fw_name, false);
>         if (!ret)
>             ret = clk_cpy_name(&parent->name,
>                                             parent_data[i].name,
>                                             false);
> ...
> 
> 
> The function clk_cpy_name() is called with the parameter "mus_exist"
> to true in the path "parent_names" and false
> in the path "parent_data". Therefore, in the path "parent_data" it is
> allowed that parent-> name is not set.
> In doing so, therefore, the change would not even be backward compatible.
> 
> So, IMHO, there are 2 possible options:
>  1 okay to use parent_data, but we keep using of_clk_get_parent_name
> () to set parent_data::name.
>  2 okay to use the version v2 of the patch.
> 
> What do you think?

I am confused.

The struct clk_parent_data::name being used is whatever string is
returned by of_clk_get_parent_name(node, 0). That is the same as setting
struct clk_parent_data::index to 0, and not assigning the 'name' or
'fw_name' field of the parent data structure. This is a compatible
change because of_clk_get_parent_name() is getting the name of the clk
in 'clocks' for 'node' at index 0. Using the index 0 in clk_parent_data
tells clk framework that the parent of the clk being registered is the
clk in 'clocks' for the 'dev->node' that is passed in during
clk_register(). If you don't have a device pointer, use
of_clk_hw_register() to pass 'node' directly. It looks like you will
have to do that in this case to get the node pointer registered with
this clk.