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

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Message-ID: <e4dd46b6-3582-129b-e75b-085571abaf72@roeck-us.net>
Date:   Wed, 8 Mar 2023 03:47:10 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Yassine Oudjana <yassine.oudjana@...il.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.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 3/2/23 04:40, Yassine Oudjana wrote:
> 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.
> 

This is two functional changes in one patch. Also, the "may be needed"
is vague. It is either needed or it isn't.

> 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 at the very least misleading. It appears to confuse
"reset" (which is triggered by writing a specific value into the
WDT_SWRST register) with the action to be taken when the watchdog
triggers. The code below does not trigger the watchdog; it is
supposed to trigger a soft reset, which should be independent
of the above.

So this needs more explanation than just "issue a system reset
instead of an IRQ", because that is presumably not supposed to
be what is happening when writing into the WDT_SWRST register.

The above also doesn't explain what is supposed to happen if
WDT_MODE_EXRST_EN is not set, adding more to the confusion.

Guenter

>   	while (1) {
>   		writel(WDT_SWRST_KEY, wdt_base + WDT_SWRST);
>   		mdelay(5);
> @@ -443,6 +454,7 @@ static int mtk_wdt_resume(struct device *dev)
>   static const struct of_device_id mtk_wdt_dt_ids[] = {
>   	{ .compatible = "mediatek,mt2712-wdt", .data = &mt2712_data },
>   	{ .compatible = "mediatek,mt6589-wdt" },
> +	{ .compatible = "mediatek,mt6735-wdt", .data = &mt6735_data },
>   	{ .compatible = "mediatek,mt6795-wdt", .data = &mt6795_data },
>   	{ .compatible = "mediatek,mt7986-wdt", .data = &mt7986_data },
>   	{ .compatible = "mediatek,mt8183-wdt", .data = &mt8183_data },