linux-kernel - Re: [PATCH v3 2/3] thermal: rockchip: ensure the otp states before resetting the controller

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Date:	Fri, 23 Oct 2015 00:04:55 -0400
From:	Doug Anderson <dianders@...omium.org>
To:	Caesar Wang <wxt@...k-chips.com>
Cc:	Heiko Stuebner <heiko@...ech.de>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Eduardo Valentin <edubezval@...il.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	Zhang Rui <rui.zhang@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 2/3] thermal: rockchip: ensure the otp states before
 resetting the controller

Caesar,

On Thu, Oct 22, 2015 at 9:54 PM, Caesar Wang <wxt@...k-chips.com> wrote:
> We need the OTP pin is gpio state before resetting the TSADC controller,
> since the tshut polarity will generate a high signal.
>
> Says:
> The TSHUT temperature is setting more than 80 degree, the
> default tshut polarity is high.
>
> If T > 80C, the OTP output the high signal.
> If T < 80C, the OTP output the low signal.
>
> On the moment, the tshut polarity will be low in a short period of time
> if the TSADC controller is reset.
>
> So:
> If T < 80C, the OTP output the High Signal.
> If T > 80C, the OTP output the Low Signal.
>
> In some cases, the OTP pin is connected to the PMIC, maybe the PMIC can
> accept the reset response time to avoid this issue.
> In other words, the system will be always reboot if we
> make the OTP pin is connected the others IC to control the power.
>
> Signed-off-by: Caesar Wang <wxt@...k-chips.com>
>
> ---
>
> Changes in v3:
>   - Add the pinctrl state for in the suspend/resume.
>
> Changes in v2: None
> Changes in v1: None
>
>  drivers/thermal/rockchip_thermal.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/thermal/rockchip_thermal.c b/drivers/thermal/rockchip_thermal.c
> index c89ffb2..3b8fbda 100644
> --- a/drivers/thermal/rockchip_thermal.c
> +++ b/drivers/thermal/rockchip_thermal.c
> @@ -642,6 +642,8 @@ static int __maybe_unused rockchip_thermal_suspend(struct device *dev)
>         clk_disable(thermal->pclk);
>         clk_disable(thermal->clk);
>
> +       pinctrl_pm_select_sleep_state(dev);
> +
>         return 0;
>  }
>
> @@ -678,6 +680,8 @@ static int __maybe_unused rockchip_thermal_resume(struct device *dev)
>         for (i = 0; i < ARRAY_SIZE(thermal->sensors); i++)
>                 rockchip_thermal_toggle_sensor(&thermal->sensors[i], true);
>
> +       pinctrl_pm_select_default_state(dev);
> +
>         return 0;
>  }

The patch looks totally fine, but the description is a little
confusing.  Reading this patch it's all about adding support for the
"sleep" state in the tsadc driver, but nothing in the description
talks about that.  I'd expect something like:

thermal: rockchip: support the sleep pinctrl state to avoid glitches in s2r

When we come out of system suspend state (S3) the tsadc will have been
reset and back at its default state.  While reprogramming the tsadc
it's possible that we'll glitch the output and unintentionally cause
the "over temperature" GPIO to be asserted.  Since the over
temperature GPIO is often hooked up to something that will cause a
reboot or shutdown in hardware, this glitch can be catastrophic on
some boards.

We'll add support for selecting the "sleep" pinctrl state at suspend
time.  Boards can use this to effectively disable the tsadc at suspend
time and avoid glitches when the system is resumed.

---

Note that although this pinctrl approach is fine IMHO, I am left
wondering whether we could just change the tsadc init sequence to
avoid the glitch.  I can't easily test myself, but if we can program
the temperatures before re-enabling the tsadc would it avoid the
problem too?  Like could we just swap things like:

                thermal->chip->set_tshut_temp(id, thermal->regs,
                                              thermal->hw_shut_temp);
                thermal->chip->set_tshut_mode(id, thermal->regs,
                                              thermal->tshut_mode);


Does that help?


-Doug
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