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

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Message-ID: <f9b09f59-a222-4b75-a6ef-c7fb7c2cff9e@gmail.com>
Date: Wed, 16 Oct 2024 12:26:26 +0300
From: Yassine Oudjana <yassine.oudjana@...il.com>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 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>
Cc: 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 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. I'm still not quite sure how the 
watchdog works but it seems to me like it's supposed to be started from 
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. According to 
the datasheet, setting WDT_MODE_IRQ_EN configures TOPRGU to send an IRQ 
on system reset event (either watchdog timeout or software watchdog 
reset) while clearing it makes it actually issue a system reset. What 
can I do in this case?