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

On 05/26/2016 03:54 PM, Guenter Roeck wrote:

On 05/26/2016 12:51 AM, Neil Armstrong wrote:

quoted

Add watchdog specific driver for Amlogic Meson GXBB SoC.

Wondering - why RFC ?

For these precious comments !
Thanks Guenter.

quoted

Signed-off-by: Neil Armstrong <redacted>
---
  drivers/watchdog/Makefile         |   1 +
  drivers/watchdog/meson_gxbb_wdt.c | 287 ++++++++++++++++++++++++++++++++++++++
  2 files changed, 288 insertions(+)
  create mode 100644 drivers/watchdog/meson_gxbb_wdt.c

diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index 9bde095..7679d93 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile

[...]

quoted

+
+unsigned int meson_gxbb_wdt_status(struct watchdog_device *wdt_dev)
+{
+    struct meson_gxbb_wdt *data = watchdog_get_drvdata(wdt_dev);
+
+    return !!(readl(data->reg_base + GXBB_WDT_CTRL_REG) & GXBB_WDT_CTRL_EN);

This function is not supposed to return 0/1 but a bit mask with relevant
WDIOF_bits set. sbsa_gwdt.c is buggy (oops, and I reviewed it ;-), so
please don't use it as example; it doesn't make much sense to return
a kernel-only flag to user space.

Overall I would suggest to not implement the function at all. We'll have
to revisit it - its current implementation in the watchdog core does not
make much sense and for the most part only returns 0 to user space.
The only driver implementing it (sbsa) returns a bad value. It is also
_not_ supposed to return the "watchdog running" status as currently
implemented (there is no WDIOF_ flag indicating that the watchdog is
running).

Ok, will remove it.

quoted

+}
+
+int meson_gxbb_wdt_ping(struct watchdog_device *wdt_dev)
+{
+    struct meson_gxbb_wdt *data = watchdog_get_drvdata(wdt_dev);
+
+    writel(0, data->reg_base + GXBB_WDT_RSET_REG);
+
+    return 0;
+}
+
+int meson_gxbb_wdt_set_timeout(struct watchdog_device *wdt_dev,
+                   unsigned int timeout)
+{
+    struct meson_gxbb_wdt *data = watchdog_get_drvdata(wdt_dev);
+
+    if (watchdog_active(wdt_dev))
+        meson_gxbb_wdt_stop(wdt_dev);
+

Is the stop/start sequence mandatory ? It leaves the system unprotected
for a few cycles, so it is undesirable.

No, it's not mandatory, it's a good point.

quoted

+
+    data->wdt_dev.parent = &pdev->dev;
+    data->wdt_dev.info = &meson_gxbb_wdt_info;
+    data->wdt_dev.ops = &meson_gxbb_wdt_ops;
+    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.

quoted

+    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.

quoted

+    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) |
+        GXBB_WDT_CTRL_EE_RESET |
+        GXBB_WDT_CTRL_CLK_EN |
+        GXBB_WDT_CTRL_CLKDIV_EN,
+        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.

quoted

+    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.