[U-Boot] [Patch v3 4/4] thermal: imx_thermal: use CPU temperature grade for trip points

[Tim Harvey]

On Mon, May 18, 2015 at 6:56 AM, Tim Harvey <tharvey at gateworks.com> wrote:
> Replace the hard-coded values for min/max/passive with values derived from
> the CPU temperature grade.
>
> Signed-off-by: Tim Harvey <tharvey at gateworks.com>
> ---
>  drivers/thermal/imx_thermal.c | 29 +++++++++++++++++++----------
>  1 file changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/thermal/imx_thermal.c b/drivers/thermal/imx_thermal.c
<snip>
> -#define TEMPERATURE_MIN                -40
> -#define TEMPERATURE_HOT                80
> -#define TEMPERATURE_MAX                125
<snip>
> @@ -119,11 +124,12 @@ static int read_cpu_temperature(struct udevice *dev)
>
>  int imx_thermal_get_temp(struct udevice *dev, int *temp)
>  {
> +       struct thermal_data *priv = dev_get_priv(dev);
>         int cpu_tmp = 0;
>
>         cpu_tmp = read_cpu_temperature(dev);
> -       while (cpu_tmp > TEMPERATURE_MIN && cpu_tmp < TEMPERATURE_MAX) {
> -               if (cpu_tmp >= TEMPERATURE_HOT) {
> +       while (cpu_tmp > priv->minc && cpu_tmp < priv->maxc) {
> +               if (cpu_tmp >= priv->passive) {
>                         printf("CPU Temperature is %d C, too hot to boot, waiting...\n",
>                                cpu_tmp);
>                         udelay(5000000);

Ye,

I'm curious where you got your previous hard-coded values of -40/80/125 from?

The range of -40 to 125 makes me think it was assumed that the IMX6
was Automotive grade (probably a bad assumption) but I'm more curious
about the value of 80C that kicks in this busywait loop above.

<snip>
> +       /* set passive cooling temp to max - 20C */
> +       get_cpu_temp_grade(&priv->minc, &priv->maxc);
> +       priv->passive = priv->maxc - 20;
> +       priv->fuse = fuse;
>

In my patch here I am calling your TEMPERATURE_HOT the 'passive' temp
and setting it to maxc-20 which for an industrial grade CPU with a max
of 105C is 85C.

Do we really want to sit in a busywait loop if the board is too hot
and if so isn't maxc-20 way too aggressive? I think that I should
re-work this patch and set 'passive' to 'maxc' or maybe just a few C
under it instead of 20C. Until then I'll need to disable
CONFIG_IMX6_THERMAL for our board because it doesn't allow us to even
run at an ambient temperature of 80C with an intdustrial processor
(80C is the point at which the CPU hits 85C at 800Mhz in U-Boot on our
board).

Tim