Re: [PATCH v2 0/2] Add a watchdog driver that uses ARM Secure Monitor Calls.

From: Xingyu Chen <xingyu.chen@amlogic.com>
To: Julius Werner <jwerner@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
	Yonghui Yu <yonghui.yu@amlogic.com>,
	Leonard Crestez <leonard.crestez@nxp.com>,
	Will Deacon <will@kernel.org>, Rob Herring <robh@kernel.org>,
	Wim Van Sebroeck <wim@linux-watchdog.org>,
	Anson Huang <Anson.Huang@nxp.com>,
	Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
	Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Guenter Roeck <linux@roeck-us.net>,
	devicetree@vger.kernel.org,
	LINUX-WATCHDOG <linux-watchdog@vger.kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	"moderated list:ARM/Mediatek SoC support"
	<linux-mediatek@lists.infradead.org>,
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	<linux-amlogic@lists.infradead.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
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	Jianxin Pan <jianxin.pan@amlogic.com>,
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	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Vinod Koul <vkoul@kernel.org>, Olof Johansson <olof@lixom.net>,
	Shawn Guo <shawnguo@kernel.org>,
	"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH v2 0/2] Add a watchdog driver that uses ARM Secure Monitor Calls.
Date: Thu, 16 Apr 2020 11:23:39 +0800	[thread overview]
Message-ID: <ea5ae44f-8b63-d34d-b313-c8deeafd86e1@amlogic.com> (raw)
In-Reply-To: <CAODwPW9RSB37+4EJ2QXAwz=ShFB23L1GKC2mLYE5L5JuQR2tPw@mail.gmail.com>

Hi,Julius

On 2020/4/16 6:29, Julius Werner wrote:
>> In addition, It looks more reasonable to use the "msec" as the unit of
>> timeout parameter for the ATF fw interface with SMCWD_SET_TIMEOUT:
>>
>> - The fw interface will compatible with the uboot generic watchdog
>> interface at [0], and there is no need to convert timeout from msec
>> to sec.
> 
> I think we're trying hard to keep this compatible to a Trusted
> Firmware counterpart that we have already shipped, so we would prefer
> to keep it at seconds if possible. That's what the Linux watchdog core
> uses as well after all, so it just seems natural. I don't really see
> how what U-Boot does would have anything to do with this.

If the uboot introduces a smcwd driver, and it maybe work like this:

static const struct wdt_ops XXX_wdt_ops = {
	.start = XXX_wdt_start,
	...
}

static int XXX_wdt_start(struct udevice *dev, u64 ms, ulong flags) {
	timeout =  ms / 1000;  //convert timeout from msec to sec.
	smcwd_call(SMCWD_SET_TIMEOUT, timeout, NULL);
	smcwd_call(SMCWD_ENABLE, 0, NULL);
}

Best Regards
> 
>> - Some vendor's watchdog may be not support the "wdt_trigger_reset"
>> reset operation, but they can use the method below to reset the system
>> by the watchdog right now.
>>
>> watchdog_set_time(1);  //1ms
>> watchdog_enable();
> 
> They can still do that but they should do that on the Trusted Firmware
> side. Emulating a missing reset functionality should be handled by the
> hardware abstraction layer (in this case Trusted Firmware), not at the
> Linux API level. So Linux would still send a PSCI_SYSTEM_RESET SMC,
> but then Trusted Firmware can choose to implement that by setting the
> watchdog to the smallest possible timeout (which it can because it's
> accessing it directly, not through this SMC interface) and letting it
> expire.
> 
> .
> 

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