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

[Christopher Bostic]

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@xxxxxxxxxxxxxxxxxx>
> > > > ---
> > > > 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);