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

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Date:   Wed, 28 Jun 2017 08:08:46 -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 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.

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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