linux-kernel - Re: [PATCH v2 2/2] drivers/watchdog: ASPEED reference dev tree properties for config

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Message-Id: <38e57720-9728-9377-2a16-adc8ce430ca0@linux.vnet.ibm.com>
Date:   Wed, 28 Jun 2017 09:59:22 -0500
From:   Christopher Bostic <cbostic@...ux.vnet.ibm.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     wim@...ana.be, robh+dt@...nel.org, mark.rutland@....com,
        joel@....id.au, linux-watchdog@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] drivers/watchdog: ASPEED reference dev tree
 properties for config



On 6/28/17 9:54 AM, Guenter Roeck wrote:
> On Wed, Jun 28, 2017 at 09:29:50AM -0500, Christopher Bostic wrote:
>>
>> On 6/28/17 6:31 AM, Guenter Roeck wrote:
>>> On 06/27/2017 02:17 PM, Christopher Bostic wrote:
>>>> Reference the system device tree when configuring the watchdog
>>>> engines.  Set external signal mode on timeout if specified.
>>>> Set system reset on timeout if specified.
>>>>
>>>> Signed-off-by: Christopher Bostic <cbostic@...ux.vnet.ibm.com>
>>>> ---
>>>> v2 - Change of_get_property() to of_property_read_bool()
>>>>     - Remove redundant check for NULL struct device_node pointer
>>>>     - Optional property names now start with prefix 'aspeed,'
>>>> ---
>>>>   drivers/watchdog/aspeed_wdt.c | 13 +++++++++++--
>>>>   1 file changed, 11 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/watchdog/aspeed_wdt.c
>>>> b/drivers/watchdog/aspeed_wdt.c
>>>> index 1c65258..71ce5f5 100644
>>>> --- a/drivers/watchdog/aspeed_wdt.c
>>>> +++ b/drivers/watchdog/aspeed_wdt.c
>>>> @@ -140,6 +140,7 @@ static int aspeed_wdt_probe(struct platform_device
>>>> *pdev)
>>>>   {
>>>>       struct aspeed_wdt *wdt;
>>>>       struct resource *res;
>>>> +    struct device_node *np;
>>>>       int ret;
>>>>         wdt = devm_kzalloc(&pdev->dev, sizeof(*wdt), GFP_KERNEL);
>>>> @@ -170,8 +171,16 @@ static int aspeed_wdt_probe(struct platform_device
>>>> *pdev)
>>>>        * the SOC and not the full chip
>>>>        */
>>>>       wdt->ctrl = WDT_CTRL_RESET_MODE_SOC |
>>>> -        WDT_CTRL_1MHZ_CLK |
>>>> -        WDT_CTRL_RESET_SYSTEM;
>>>> +        WDT_CTRL_1MHZ_CLK;
>>>> +
>>>> +    np = pdev->dev.of_node;
>>>> +    if (of_property_read_bool(np, "aspeed,sys-reset"))
>>>> +        wdt->ctrl |= WDT_CTRL_RESET_SYSTEM;
>>>> +
>>> For backward compatibility, this should default to WDT_CTRL_RESET_SYSTEM
>>> if no optional property is provided.
>>>
>> I had the logic inverted for this property in a previous patch.  The
>> property was 'no-system-reset' so that when not present the default was to
>> set WDT_CTRL_RESET_SYSTEM.   As it is in this patch, the only way to
>> indicate that no system reset is to be done is to not specify the property.
>> No system reset is desired under circumstances when another wdt engine is to
>> be responsible for this.   Given the issue with backward compatibility
>> that's not a solution.  Given this, would creating a property
>> 'no-system-reset' be acceptable?
>>
> Sorry, I fail to see the problem. There are half a dozen properties. What is the
> problem with having a default if no property is specified ? Your default is "do
> nothing", which does not really make any sense to me. If the user wants the
> watchdog to do nothing, the simple means to accomplish that would be to not
> instantiate it.
>
> Sure, that means specifying "system-reset" is redundant, but I don't see a
> problem with that either. But I do see a problem with loading a watchdog driver
> that doesn't do anything.
>
> If there is really some use case where it makes sense to load a watchdog driver
> and have it do nothing, please explain and provide a respective devicetree
> property. "aspeed,do-nothing" (or whatever similar) doesn't sound good, but
> at least makes it obvious that the driver isn't doing anything besides
> creating a false sense of "the system is watchdog protected".
If system-reset is not wanted there are other properties that might 
still be needed, for example
ARM reset only.   We'd still want to instantiate it.

Thanks,
Chris
>
> Thanks,
> Guenter
>
>
>> Thanks,
>> Chris
>>
>>>> +    if (of_property_read_bool(np, "aspeed,external-signal"))
>>>> +        wdt->ctrl |= WDT_CTRL_WDT_EXT;
>>>> +
>>>> +    writel(wdt->ctrl, wdt->base + WDT_CTRL);
>>>>         if (readl(wdt->base + WDT_CTRL) & WDT_CTRL_ENABLE)  {
>>>>           aspeed_wdt_start(&wdt->wdd);
>>>>