Re: [RFC PATCH 1/3] watchdog: Add Meson GXBB Watchdog Driver

From: Guenter Roeck
Date: Fri May 27 2016 - 09:49:14 EST

On 05/27/2016 01:25 AM, Neil Armstrong wrote:
[ ... ]
+ data->wdt_dev.max_hw_heartbeat_ms = GXBB_WDT_TCNT_SETUP_MASK;
+ data->wdt_dev.min_hw_heartbeat_ms = 1;

Does the device require a minimum time between heartbeats ?
Just asking, because you violate it yourself below.

If you want to set the minimum timeout, that would be min_timeout.

Ok, these values are not very clear actually.

Hmmm .. yes, reading the description again, it doesn't really describe well
what it is doing. Essentially, min_hw_heartbeat_ms is enforced by the watchdog
core, and should be used if a watchdog hardware can not tolerate short intervals
between heartbeats. min_timeout is the minimum timeout value configurable from
user space.

+ data->wdt_dev.timeout = DEFAULT_TIMEOUT;
+ watchdog_set_drvdata(&data->wdt_dev, data);
+ watchdog_init_timeout(&data->wdt_dev, DEFAULT_TIMEOUT, &pdev->dev);

DEFAULT_TIMEOUT is unnecessary here. Since the default timeout is already set,
it makes the call useless.

+ ret = watchdog_register_device(&data->wdt_dev);
+ if (ret)
+ return ret;
+ /* Setup with 1ms timebase */
+ writel(((clk_get_rate(data->clk) / 1000) & GXBB_WDT_CTRL_DIV_MASK) |
+ data->reg_base + GXBB_WDT_CTRL_REG);
+ meson_gxbb_wdt_set_timeout(&data->wdt_dev, data->wdt_dev.timeout);

set_timeout already calls the ping function. Also, the functions should be called
prior to watchdog registration to avoid race conditions.

+ meson_gxbb_wdt_ping(&data->wdt_dev);

This is unusual. If the watchdog can be already running, it might make sense
to tell the core about it (set WDOG_HW_RUNNING in the status field), so it
can send heartbeats until user space opens the device.

Yes, since meson_gxbb_wdt_set_timeout() already ping, this is useless.

Not only that - if the watchdog _is_ already running at boot time, you should
really set WDOG_HW_RUNNING to let the watchdog core know. You status function
would come handy there.

if (meson_gxbb_wdt_status(data)) // note the changed parameter
set_bit(WDOG_HW_RUNNING, &data->wdt_dev.status);