Date:   Wed, 28 Jun 2017 09:06:49 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Christopher Bostic <cbostic@...ux.vnet.ibm.com>
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 Wed, Jun 28, 2017 at 10:55:08AM -0500, Christopher Bostic wrote:
> 
> 
> On 6/28/17 10:08 AM, Guenter Roeck wrote:
> >On Wed, Jun 28, 2017 at 09:59:22AM -0500, Christopher Bostic wrote:
> >>
> >>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.
> >>
> >But then you would presumably specify that property, so there would be one.
> >The question here is what to do if _no_ property is provided.
> I agree that the default should be to perform a system reset  when no
> property is provided.  I will make that change.   Additionally for backwards
> compatibility the SOC reset should be enabled by default when no property is
> provided.   The other parameters are not configured in the watchdog control
> register if no property is provided.
> 
> There is still a need to to configure for no system reset.  For example,
> optional parameter 'aspeed,no-sys-reset' that can be specified if system
> reset is to be disabled.  In addition the default 'SOC reset enabled'
> behavior could be disabled with an optional parameter 'aspeed,no-soc-reset'.
> 
> Why would there even be a need configure for no system reset?  The external
> mode 'wdt ext: External signal enable after timeout' can be sent off chip
> even if system reset is disabled.  The watchdog is doing something in this
> case and would require wdt instantiation.
> 

Wouldn't that be "aspeed,external-signal" ?

Guenter

> Hope this is more clear, sorry for the confusion.
> 
> Thanks,
> -Chris AST2500 Software Programming Guide
> >Sorry, I don't get your point.
> >
> >Guenter
> >
> >>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);
> >>>>>>
> >>--
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> 

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