linux-kernel - Re: [PATCH v7 5/5] rockchip/soc/drivers: Add DTPM description for rk3399

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Date:   Fri, 28 Jan 2022 16:13:11 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Heiko Stübner <heiko@...ech.de>, rjw@...ysocki.net
Cc:     robh@...nel.org, lukasz.luba@....com, arnd@...aro.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "moderated list:ARM/Rockchip SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/Rockchip SoC support" 
        <linux-rockchip@...ts.infradead.org>
Subject: Re: [PATCH v7 5/5] rockchip/soc/drivers: Add DTPM description for
 rk3399


Hi Heiko,

thanks for your comments

On 28/01/2022 11:19, Heiko Stübner wrote:
> Am Dienstag, 25. Januar 2022, 18:18:09 CET schrieb Daniel Lezcano:
>> The DTPM framework does support now the hierarchy description.
>>
>> The platform specific code can call the hierarchy creation function
>> with an array of struct dtpm_node pointing to their parent.
>>
>> This patch provides a description of the big / Little CPUs and the
>> GPU and tie them together under a virtual 'package' name. Only rk3399 is
>> described now.
>>
>> The description could be extended in the future with the memory
>> controller with devfreq.
>>
>> The description is always a module and it describes the soft
>> dependencies. The userspace has to load the softdeps module in the
>> right order.
>>
>> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>

[ ... ]

>> +static struct dtpm_node __initdata rk3399_hierarchy[] = {
> 
> The driver is tristate so buildable as module but uses __initdata.
> As it depends on panfrost (which also can be a module) you
> probably want a "__initdata_or_module" here .

Well, actually the dependency is wrong.

It should be:

	depends on DTPM && m

It will be compiled always as a module.

Referring to the Documentation/kernel-hacking/hacking.rst

"After boot, the kernel frees up a special section; functions marked with
``__init`` and data structures marked with ``__initdata`` are dropped
after boot is complete: similarly modules discard this memory after
initialization."

So after the module is loaded and the hierarchy is created, nothing will 
stay in memory (except the future module exit function)


>> +	[0]{ .name = "rk3399",
>> +	     .type = DTPM_NODE_VIRTUAL },
>> +	[1]{ .name = "package",
>> +	     .type = DTPM_NODE_VIRTUAL,
>> +	     .parent = &rk3399_hierarchy[0] },
>> +	[2]{ .name = "/cpus/cpu@0",
>> +	     .type = DTPM_NODE_DT,
>> +	     .parent = &rk3399_hierarchy[1] },
>> +	[3]{ .name = "/cpus/cpu@1",
>> +	     .type = DTPM_NODE_DT,
>> +	     .parent = &rk3399_hierarchy[1] },
>> +	[4]{ .name = "/cpus/cpu@2",
>> +	     .type = DTPM_NODE_DT,
>> +	     .parent = &rk3399_hierarchy[1] },
>> +	[5]{ .name = "/cpus/cpu@3",
>> +	     .type = DTPM_NODE_DT,
>> +	     .parent = &rk3399_hierarchy[1] },
>> +	[6]{ .name = "/cpus/cpu@100",
>> +	     .type = DTPM_NODE_DT,
>> +	     .parent = &rk3399_hierarchy[1] },
>> +	[7]{ .name = "/cpus/cpu@101",
>> +	     .type = DTPM_NODE_DT,
>> +	     .parent = &rk3399_hierarchy[1] },
>> +	[8]{ .name = "/gpu@...a0000",
>> +	     .type = DTPM_NODE_DT,
>> +	     .parent = &rk3399_hierarchy[1] },
>> +	[9]{ },
> 
> hmm, do we want a "/* sentinel */" inside the empty last entry?
> I think that is pretty common to denote the "this one is the last entry"
> of a dynamic list ;-)

Sure

>> +};
>> +
>> +static struct of_device_id __initdata rockchip_dtpm_match_table[] = {
>> +        { .compatible = "rockchip,rk3399", .data = rk3399_hierarchy },
>> +        {},
>> +};
>> +
>> +static int __init rockchip_dtpm_init(void)
>> +{
>> +	return dtpm_create_hierarchy(rockchip_dtpm_match_table);
>> +}
>> +module_init(rockchip_dtpm_init);
> 
> Just for my understanding what happens on driver unload?

ATM it is not possible to unload it.

A second series with the hierarchy destruction will follow once this 
series is merged. The module unloading will be added here.


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