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

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Date:   Thu, 27 Aug 2020 14:40:13 +0800
From:   Yue Hu <zbestahu@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     rafael.j.wysocki@...el.com,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        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 Thu, 27 Aug 2020 11:56:46 +0530
Viresh Kumar <viresh.kumar@...aro.org> wrote:

> On 27-08-20, 14:20, Yue Hu wrote:
> > Currenly, drivers/video/backlight does not call thermal_of_cooling_device_register()
> > to register thermal cooling device. The issue happened in msm-4.19 kernel for
> > QCOM/Android platform. Backlight in msm-4.19 kernel will register thermal cooling
> > device as below:
> > 
> > +static int bd_cdev_get_max_brightness(struct thermal_cooling_device *cdev,
> > +                                 unsigned long *state)
> > +{
> > + struct backlight_device *bd = (struct backlight_device *)cdev->devdata;
> > +
> > + *state = bd->props.max_brightness;
> > +
> > + return 0;
> > +}
> > 
> > 
> > +static struct thermal_cooling_device_ops bd_cdev_ops = {
> > + .get_max_state = bd_cdev_get_max_brightness,
> > 
> > +static void backlight_cdev_register(struct device *parent,
> > +                             struct backlight_device *bd)
> > +{
> > + if (of_find_property(parent->of_node, "#cooling-cells", NULL)) {
> > +         bd->cdev = thermal_of_cooling_device_register(parent->of_node,
> > +                         (char *)dev_name(&bd->dev), bd, &bd_cdev_ops);
> > 
> > And the bd->props.max_brightness is getting from video/backlight/qcom-wled.c. Maybe
> > the driver should not assign 1024 to states/max_brightness. I'm not sure about it.
> > So i consider to change memory allocation methord. That's the origin of the patch.  
> 
> Thanks for the details. So this is not about upstream tree, as a rule
> we aren't going to make changes here for any downstream tree.

I at first thought it's a possible issue in upstream tree.

> 
> Now coming back to the downstream driver, I also don't see a point in
> returning bd->props.max_brightness as the max number of states there.
> Maybe have 10 states, each occupying bd->props.max_brightness/10
> brightness and so you will end up with 10 states only. But yeah,
> whatever downstream decides on that.
> 

Got it.

Thx.