linux-kernel - Re: [PATCH 2/2] watchdog: mtk_wdt: Add support for MT6735 WDT

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Message-Id: <WOMHLS.HLNVQWWVER5T1@gmail.com>
Date: Thu, 17 Oct 2024 09:43:44 +0300
From: yassine.oudjana@...il.com
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: Wim Van Sebroeck <wim@...ux-watchdog.org>, Guenter Roeck
	<linux@...ck-us.net>, Rob Herring <robh+dt@...nel.org>, Krzysztof Kozlowski
	<krzysztof.kozlowski+dt@...aro.org>, Matthias Brugger
	<matthias.bgg@...il.com>, Philipp Zabel <p.zabel@...gutronix.de>,
	Yassine Oudjana <y.oudjana@...tonmail.com>, linux-watchdog@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 2/2] watchdog: mtk_wdt: Add support for MT6735 WDT


On Wed, Oct 16 2024 at 11:56:31 +02:00:00, AngeloGioacchino Del Regno 
<angelogioacchino.delregno@...labora.com> wrote:
> Il 16/10/24 11:26, Yassine Oudjana ha scritto:
>> On 02/03/2023 6:15 pm, AngeloGioacchino Del Regno wrote:
>>> Il 02/03/23 13:40, Yassine Oudjana ha scritto:
>>>> From: Yassine Oudjana <y.oudjana@...tonmail.com>
>>>> 
>>>> Add support for the watchdog timer/top reset generation unit found 
>>>> on MT6735.
>>>> Disable WDT_MODE_IRQ_EN in mtk_wdt_restart in order to make TOPRGU 
>>>> assert
>>>> the SYSRST pin instead of issuing an IRQ. This change may be 
>>>> needed in other
>>>> SoCs as well.
>>>> 
>>>> Signed-off-by: Yassine Oudjana <y.oudjana@...tonmail.com>
>>>> ---
>>>>   drivers/watchdog/mtk_wdt.c | 12 ++++++++++++
>>>>   1 file changed, 12 insertions(+)
>>>> 
>>>> diff --git a/drivers/watchdog/mtk_wdt.c 
>>>> b/drivers/watchdog/mtk_wdt.c
>>>> index a9c437598e7e..5a7a7b2b3727 100644
>>>> --- a/drivers/watchdog/mtk_wdt.c
>>>> +++ b/drivers/watchdog/mtk_wdt.c
>>>> @@ -10,6 +10,7 @@
>>>>    */
>>>>   #include <dt-bindings/reset/mt2712-resets.h>
>>>> +#include <dt-bindings/reset/mediatek,mt6735-wdt.h>
>>>>   #include <dt-bindings/reset/mediatek,mt6795-resets.h>
>>>>   #include <dt-bindings/reset/mt7986-resets.h>
>>>>   #include <dt-bindings/reset/mt8183-resets.h>
>>>> @@ -82,6 +83,10 @@ static const struct mtk_wdt_data mt2712_data = {
>>>>       .toprgu_sw_rst_num = MT2712_TOPRGU_SW_RST_NUM,
>>>>   };
>>>> +static const struct mtk_wdt_data mt6735_data = {
>>>> +    .toprgu_sw_rst_num = MT6735_TOPRGU_RST_NUM,
>>>> +};
>>>> +
>>>>   static const struct mtk_wdt_data mt6795_data = {
>>>>       .toprgu_sw_rst_num = MT6795_TOPRGU_SW_RST_NUM,
>>>>   };
>>>> @@ -187,9 +192,15 @@ static int mtk_wdt_restart(struct 
>>>> watchdog_device *wdt_dev,
>>>>   {
>>>>       struct mtk_wdt_dev *mtk_wdt = watchdog_get_drvdata(wdt_dev);
>>>>       void __iomem *wdt_base;
>>>> +    u32 reg;
>>>>       wdt_base = mtk_wdt->wdt_base;
>>>> +    /* Enable reset in order to issue a system reset instead of 
>>>> an IRQ */
>>>> +    reg = readl(wdt_base + WDT_MODE);
>>>> +    reg &= ~WDT_MODE_IRQ_EN;
>>>> +    writel(reg | WDT_MODE_KEY, wdt_base + WDT_MODE);
>>> 
>>> This is unnecessary and already done in mtk_wdt_start().
>>> If you think you *require* this snippet, you most likely 
>>> misconfigured the
>>> devicetree node for your device :-)
>> 
>> Ok so mtk_wdt_start is never called.
> 
> mtk_wdt_init() says
> 
> 	if (readl(wdt_base + WDT_MODE) & WDT_MODE_EN) {
> 		set_bit(WDOG_HW_RUNNING, &wdt_dev->status);
> 		mtk_wdt_set_timeout(wdt_dev, wdt_dev->timeout);
> 	}
> 
> Your bootloader starts the watchdog. This driver will set 
> WDOG_HW_RUNNING and
> will hence prevent calling the .start() callback - that's why.

It doesn't.

WDT_MODE reads 0x5c in mtk_wdt_init if you want to see exactly how the 
bootloader is configuring it.

> 
>> I'm still not quite sure how the watchdog works but it seems to me 
>> like it's supposed to be started from userspace.
> 
> No, it's not meant to be just only used in userspace.
> 
>> I also see some drivers calling it in probe.
>> 
>> Say I don't want to use the watchdog (which I don't, all I need from 
>> TOPRGU is the resets, I don't care about the watchdog). Not 
>> starting the watchdog means I can't reset the system because all 
>> mtk_wdt_restart will do is make TOPRGU send me an IRQ that I have 
>> no use for.
> 
> If you don't want to use the watchdog, then you don't need to care 
> about bark
> interrupts and you don't need any mtk_wdt_restart() functionality at 
> all :-)

I need mtk_wdt_restart to restart my system. I shouldn't need to take 
off my phone's back cover and remove the battery every time :)

> 
I think what Guenter said makes sense. We should make sure the watchdog 
is started when calling mtk_wdt_restart or at least configured in such 
a way that we are sure it will issue a system reset.