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

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Date:   Thu, 27 Aug 2020 12:03:27 +0800
From:   Yue Hu <zbestahu@...il.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>, viresh.kumar@...aro.org
Cc:     rui.zhang@...el.com, amit.kucheria@...durent.com,
        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

On Wed, 26 Aug 2020 11:19:02 +0200
Daniel Lezcano <daniel.lezcano@...aro.org> wrote:

> 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 ?

Hi Daniel,

Now, i'm just focus on removing the kernel warning based on current code logic.
Commit 8ea229511e06 (thermal: Add cooling device's statistics in sysfs) added
the thermal statistics by viresh and viresh gived the patch an acknowledgement
in anther mail thread. 

Hi viresh,

Could you review the patch again about the question above?

Thank you.

> 
> 
> 
>