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

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Message-ID: <20200827062646.adruzyyqq5uzlteq@vireshk-i7>
Date:   Thu, 27 Aug 2020 11:56:46 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Yue Hu <zbestahu@...il.com>
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 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.

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.

-- 
viresh