linux-kernel - Re: [PATCH] thermal: sysfs: fall back to vzalloc for cooling device's statistics

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Date:   Wed, 26 Aug 2020 11:19:02 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Yue Hu <zbestahu@...il.com>
Cc:     rui.zhang@...el.com, amit.kucheria@...durent.com,
        viresh.kumar@...aro.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, huyue2@...ong.com, zbestahu@....com
Subject: Re: [PATCH] thermal: sysfs: fall back to vzalloc for cooling device's
 statistics


Hi Yue,

On 26/08/2020 04:13, Yue Hu wrote:
> On Mon, 24 Aug 2020 12:40:35 +0200
> Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
> 
>> On 18/08/2020 08:30, Yue Hu wrote:
>>> From: Yue Hu <huyue2@...ong.com>
>>>
>>> We observed warning about kzalloc() when register thermal cooling device
>>> in backlight_device_register(). backlight display can be a cooling device
>>> since reducing screen brightness will can help reduce temperature.
>>>
>>> However, ->get_max_state of backlight will assign max brightness of 1024
>>> to states. The memory size can be getting 1MB+ due to states * states.  
>>
>> What are the benefits of a 1024 states cooling device ? Is the
>> difference noticeable with a such small step ?
> 
> Okay, this issue is happened under MSM/Android platform. QCOM spmi wled driver
> will define the max brightness. We needs to fix the issue to get thermal statistics.

Let me rephrase my questions:

Don't you think there is something wrong in creating a 1024 x 1024
matrix to show transitions ?

What is the benefit of such stats ?

What is the benefit of having a 1024 states cooling device ?




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