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Subject: Re: [PATCH v2 0/2] Add a watchdog driver that uses ARM Secure Monitor
 Calls.
To:     Julius Werner <jwerner@chromium.org>
CC:     Evan Benn <evanbenn@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
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        "David S. Miller" <davem@davemloft.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        Leonard Crestez <leonard.crestez@nxp.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
        Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>,
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        Matthias Brugger <matthias.bgg@gmail.com>,
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        Valentin Schneider <valentin.schneider@arm.com>,
        Vinod Koul <vkoul@kernel.org>, Will Deacon <will@kernel.org>,
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        Jianxin Pan <jianxin.pan@amlogic.com>,
        Yonghui Yu <yonghui.yu@amlogic.com>,
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From:   Xingyu Chen <xingyu.chen@amlogic.com>
Message-ID: <ea5ae44f-8b63-d34d-b313-c8deeafd86e1@amlogic.com>
Date:   Thu, 16 Apr 2020 11:23:39 +0800
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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.
> 
> .
>