Re: [PATCH 2/3] watchdog: xilinx_wwdt: Add Versal Window watchdog mode

[Guenter Roeck <linux@roeck-us.net>]

On 7/13/21 10:29 PM, Srinivas Neeli wrote:
> Hi Guenter,
> 
> If you are fine with my justification, I will send v2 with update code.
> 

We have at least one more watchdog driver with open/closed window concepts.
This is not a "pretimeout". Please see drivers/watchdog/rti_wdt.c for an
example on how to handle this; essentially you have to set min_hw_heartbeat_ms
to the value of the closed window timeout. The watchdog core then handles
the mechanics.

You can not use "pretimeout" to set the "closed" window size; this is an
ABI abuse. There is no standard ABI for this, so if you want to have it
configurable it would have to be a module parameter.

Guenter

> Thanks
> Srinivas Neeli.
> 
> *From:* Srinivas Neeli <sneeli@xilinx.com>
> *Sent:* Wednesday, June 9, 2021 12:57 PM
> *To:* Guenter Roeck <linux@roeck-us.net>; Shubhrajyoti Datta <shubhraj@xilinx.com>; Srinivas Goud <sgoud@xilinx.com>; Michal Simek <michals@xilinx.com>
> *Cc:* wim@linux-watchdog.org; linux-watchdog@vger.kernel.org; linux-kernel@vger.kernel.org; git <git@xilinx.com>
> *Subject:* RE: [PATCH 2/3] watchdog: xilinx_wwdt: Add Versal Window watchdog mode
> 
> Hi Guenter Roeck,
> 
> Thanks for review.
> 
> Versal platform contain System watchdog Timer. It supports two functions, Those are
> 
> 1) Generic watchdog mode
> 
> 2) Window watchdog mode
> 
> Right now we are implementing window watchdog timer functionality in driver.
> 
> Features of Window watchdog mode:
> 
> - The timer contains two configurable windows( closed and open).
> 
> - The timer has to restart only in open window.
> 
> - If software tries to restart out side of open window it will generate a reset.
> 
> We have a requirement for window watchdog driver, So I  implemented window watchdog in two scenarios.
> 
> 1) With Pre-timeout
> 
> 2) With without Pre-timeout
> 
> *Scenario 1:*
> 
> With pre-timeout:
> 
> Here we will get two window concept.
> 
> 1) closed window
> 
> 2) Open window
> 
> start to pre-timeout, we are calling "*closed*" window.
> 
>  From pre-timeout to timeout we are calling “*Open*” window.
> 
> *Operations:*
> 
> start
> 
> keep alive(only in open window,  closed window we are ignoring)
> 
> stop
> 
> we don't have permission to refresh/restart our timer in closed window, So ignoring the keepalive.
> 
> Adjusted code to generate interrupt after completion of closed window. once we cross the closed window we can restart our time anytime.
> 
> Once we reaches to timeout , will get reset signal.
> 
> *Advantage:*
> 
> After getting pre-timeout notification we can reset our timer or can collect our log.
> 
> once we get interrupt we can conclude our task is not working as expected.
> 
> So we can takecare of our tasks.
> 
> *Scenario 2:*
> 
> with out pre-timeout:
> 
> It will work like general watchdog timer.
> 
> we can run keepalive anytime(as there is no closed window, only open window present).
> 
> Once we reaches to time out, will get reset.
> 
> *Operations:*
> 
> start
> 
> keep alive
> 
> stop
> 
> For more details:
> 
> https://www.xilinx.com/support/documentation/architecture-manuals/am011-versal-acap-trm.pdf <https://www.xilinx.com/support/documentation/architecture-manuals/am011-versal-acap-trm.pdf>
> 
> major comments will update in V2.
> 
>  > -----Original Message-----
> 
>  > From: Guenter Roeck <groeck7@gmail.com <mailto:groeck7@gmail.com>> On Behalf Of Guenter Roeck
> 
>  > Sent: Thursday, May 27, 2021 8:09 PM
> 
>  > To: Srinivas Neeli <sneeli@xilinx.com <mailto:sneeli@xilinx.com>>; Shubhrajyoti Datta
> 
>  > <shubhraj@xilinx.com <mailto:shubhraj@xilinx.com>>; Srinivas Goud <sgoud@xilinx.com <mailto:sgoud@xilinx.com>>; Michal Simek
> 
>  > <michals@xilinx.com <mailto:michals@xilinx.com>>
> 
>  > Cc: wim@linux-watchdog.org <mailto:wim@linux-watchdog.org>; linux-watchdog@vger.kernel.org <mailto:linux-watchdog@vger.kernel.org>; linux-
> 
>  > kernel@vger.kernel.org <mailto:kernel@vger.kernel.org>; git <git@xilinx.com <mailto:git@xilinx.com>>
> 
>  > Subject: Re: [PATCH 2/3] watchdog: xilinx_wwdt: Add Versal Window
> 
>  > watchdog mode
> 
>  >
> 
>  > The subject is confusing. This patch does not add "Versal Window watchdog
> 
>  > mode", it adds a driver which supports the Versal Window watchdog. The
> 
>  > subject should be something like "watchdog: Add Versal Window watchdog
> 
>  > driver".
> 
>  >
> 
>  > On 5/27/21 2:57 AM, Srinivas Neeli wrote:
> 
>  > > Versal watchdog driver uses Window watchdog mode. Window watchdog
> 
>  > > timer(WWDT) contains closed(first) and open(second) window with
> 
>  > > 32 bit width. WWDT will generate an interrupt after the first window
> 
>  > > timeout and reset signal after the second window timeout. Timeout and
> 
>  > > Pre-timeout configuration, Stop and Refresh trigger only in open
> 
>  > > window.
> 
>  >
> 
>  > Does that mean that userspace can not send a keepalive before the
> 
>  > pretimeout expires ? That is not how this is supposed to work. If that is the
> 
>  > case, this is not a pretimeout. Pretimeout is supposed to be used for
> 
>  > emergency handling, such as triggering a crash dump. The above description
> 
>  > as well as the code suggests that an interrupt is all but mandatory.
> 
>  >
> 
>  > Assuming that is all the case, ie that keepalive is only possible after the
> 
>  > interrupt was received, and that timeout updates are also only possible after
> 
>  > an interrupt was received, one possible handling would to record that a
> 
>  > keepalive was received, and to record that a request to update the timeout
> 
>  > was received if that happens while the window is closed. Then, when the
> 
>  > interrupt is received, those actions can be applied. Otherwise, if there was
> 
>  > no keepalive request prior to the interrupt, the interrupt handler would call
> 
>  > watchdog_notify_pretimeout().
> 
>  >
> 
>  > Of course, this is all just guesswork.
> 
>  >
> 
>  > More comments below.
> 
>  >
> 
>  > Guenter
> 
>  >
> 
>  > >
> 
>  > > Signed-off-by: Srinivas Neeli <srinivas.neeli@xilinx.com <mailto:srinivas.neeli@xilinx.com>>
> 
>  > > ---
> 
>  > >   drivers/watchdog/Kconfig       |  16 ++
> 
>  > >   drivers/watchdog/Makefile      |   1 +
> 
>  > >   drivers/watchdog/xilinx_wwdt.c | 382
> 
>  > +++++++++++++++++++++++++++++++++
> 
>  > >   3 files changed, 399 insertions(+)
> 
>  > >   create mode 100644 drivers/watchdog/xilinx_wwdt.c
> 
>  > >
> 
>  > > diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig index
> 
>  > > 355100dad60a..2ed17f278783 100644
> 
>  > > --- a/drivers/watchdog/Kconfig
> 
>  > > +++ b/drivers/watchdog/Kconfig
> 
>  > > @@ -307,6 +307,22 @@ config XILINX_WATCHDOG
> 
>  > >            To compile this driver as a module, choose M here: the
> 
>  > >            module will be called of_xilinx_wdt.
> 
>  > >
> 
>  > > +config XILINX_WINDOW_WATCHDOG
> 
>  > > +      tristate "Xilinx Window Watchdog timer"
> 
>  > > +      depends on HAS_IOMEM
> 
>  > > +      select WATCHDOG_CORE
> 
>  > > +      help
> 
>  > > +        Window Watchdog driver for the versal_wwdt ip core.
> 
>  > > +        Window watchdog timer(WWDT) contains closed(first) and
> 
>  > > +        open(second) window with 32 bit width. WWDT will generate
> 
>  > > +        an interrupt after the first window timeout and reset
> 
>  > > +        signal after the second window timeout. Timeout and
> 
>  > > +        Pre-timeout configuration, Stop and Refresh trigger
> 
>  > > +        only in open window.
> 
>  > > +
> 
>  > > +        To compile this driver as a module, choose M here: the
> 
>  > > +        module will be called xilinx_wwdt.
> 
>  > > +
> 
>  > >   config ZIIRAVE_WATCHDOG
> 
>  > >          tristate "Zodiac RAVE Watchdog Timer"
> 
>  > >          depends on I2C
> 
>  > > diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> 
>  > > index a7eade8b4d45..97d10c3d39c7 100644
> 
>  > > --- a/drivers/watchdog/Makefile
> 
>  > > +++ b/drivers/watchdog/Makefile
> 
>  > > @@ -148,6 +148,7 @@ obj-$(CONFIG_M54xx_WATCHDOG) +=
> 
>  > m54xx_wdt.o
> 
>  > >
> 
>  > >   # MicroBlaze Architecture
> 
>  > >   obj-$(CONFIG_XILINX_WATCHDOG) += of_xilinx_wdt.o
> 
>  > > +obj-$(CONFIG_XILINX_WINDOW_WATCHDOG) += xilinx_wwdt.o
> 
>  > >
> 
>  > >   # MIPS Architecture
> 
>  > >   obj-$(CONFIG_ATH79_WDT) += ath79_wdt.o diff --git
> 
>  > > a/drivers/watchdog/xilinx_wwdt.c b/drivers/watchdog/xilinx_wwdt.c new
> 
>  > > file mode 100644 index 000000000000..8fa2cb2225e8
> 
>  > > --- /dev/null
> 
>  > > +++ b/drivers/watchdog/xilinx_wwdt.c
> 
>  > > @@ -0,0 +1,382 @@
> 
>  > > +// SPDX-License-Identifier: GPL-2.0
> 
>  > > +/*
> 
>  > > + * Window Watchdog Device Driver for Xilinx Versal WWDT
> 
>  > > + *
> 
>  > > + * (C) Copyright 2021 Xilinx, Inc.
> 
>  > > + */
> 
>  > > +
> 
>  > > +#include <linux/clk.h>
> 
>  > > +#include <linux/interrupt.h>
> 
>  > > +#include <linux/io.h>
> 
>  > > +#include <linux/ioport.h>
> 
>  > > +#include <linux/of_device.h>
> 
>  > > +#include <linux/of_address.h>
> 
>  > > +#include <linux/module.h>
> 
>  > > +#include <linux/watchdog.h>
> 
>  > > +
> 
>  > > +#define XWWDT_DEFAULT_TIMEOUT           40
> 
>  > > +#define XWWDT_MIN_TIMEOUT    1
> 
>  > > +#define XWWDT_MAX_TIMEOUT   42
> 
>  > > +
> 
>  > > +/* Register offsets for the WWdt device */
> 
>  > > +#define XWWDT_MWR_OFFSET      0x00
> 
>  > > +#define XWWDT_ESR_OFFSET          0x04
> 
>  > > +#define XWWDT_FCR_OFFSET          0x08
> 
>  > > +#define XWWDT_FWR_OFFSET        0x0c
> 
>  > > +#define XWWDT_SWR_OFFSET        0x10
> 
>  > > +
> 
>  > > +/* Master Write Control Register Masks */
> 
>  > > +#define XWWDT_MWR_MASK                         BIT(0)
> 
>  > > +
> 
>  > > +/* Enable and Status Register Masks */
> 
>  > > +#define XWWDT_ESR_WINT_MASK BIT(16)
> 
>  > > +#define XWWDT_ESR_WSW_MASK BIT(8)
> 
>  > > +#define XWWDT_ESR_WEN_MASK BIT(0)
> 
>  > > +
> 
>  > > +/* Function control Register Masks */
> 
>  > > +#define XWWDT_SBC_MASK                            0xFF00
> 
>  > > +#define XWWDT_SBC_SHIFT                             16
> 
>  > > +#define XWWDT_BSS_MASK                             0xC0
> 
>  > > +
> 
>  > > +static int wwdt_timeout;
> 
>  > > +
> 
>  > > +module_param(wwdt_timeout, int, 0644);
> 
>  > MODULE_PARM_DESC(wwdt_timeout,
> 
>  > > +                      "Watchdog time in seconds. (default="
> 
>  > > +                      __MODULE_STRING(XWWDT_DEFAULT_TIMEOUT) ")");
> 
>  > > +
> 
>  > > +struct xwwdt_device {
> 
>  > > +      void __iomem *base;
> 
>  > > +      spinlock_t spinlock; /* spinlock for register handling */
> 
>  > > +      struct watchdog_device xilinx_wwdt_wdd;
> 
>  > > +      struct clk *clk;
> 
>  > > +      int irq;
> 
>  > > +};
> 
>  > > +
> 
>  > > +static int is_wwdt_in_closed_window(struct watchdog_device *wdd)
> 
>  >
> 
>  > should return bool
> 
> Will update in V2.
> 
>  >
> 
>  > > +{
> 
>  > > +      u32 control_status_reg;
> 
>  > > +      struct xwwdt_device *xdev = watchdog_get_drvdata(wdd);
> 
>  > > +
> 
>  > > +      spin_lock(&xdev->spinlock);
> 
>  > > +      control_status_reg = ioread32(xdev->base + XWWDT_ESR_OFFSET);
> 
>  > > +      spin_unlock(&xdev->spinlock);
> 
>  > > +      if (control_status_reg & XWWDT_ESR_WEN_MASK)
> 
>  > > +                      if (!(control_status_reg & XWWDT_ESR_WSW_MASK))
> 
>  > > +                                      return 0;
> 
>  > > +
> 
>  > > +      return 1;
> 
>  >
> 
>  > Can be written as expresion without if statement
> 
> Will update in V2
> 
>  >
> 
>  > > +}
> 
>  > > +
> 
>  > > +static int xilinx_wwdt_start(struct watchdog_device *wdd) {
> 
>  > > +      struct xwwdt_device *xdev = watchdog_get_drvdata(wdd);
> 
>  > > +      struct watchdog_device *xilinx_wwdt_wdd = &xdev-
> 
>  > >xilinx_wwdt_wdd;
> 
>  > > +      u64 time_out, pre_timeout, count;
> 
>  > > +      u32 control_status_reg, fcr;
> 
>  > > +      int ret;
> 
>  > > +
> 
>  > > +      count = clk_get_rate(xdev->clk);
> 
>  > > +      if (!count)
> 
>  > > +                      return -EINVAL;
> 
>  > > +
> 
>  > Is there a reason to believe that the clock rate can change ?
> 
>  > If not I would suggest to read it once and store it in struct xwwdt_device.
> 
> Will update in V2.
> 
>  >
> 
>  > > +      /* Calculate timeout count */
> 
>  > > +      pre_timeout = count * wdd->pretimeout;
> 
>  > > +      time_out = count * wdd->timeout;
> 
>  > > +      if (!watchdog_active(xilinx_wwdt_wdd)) {
> 
>  > > +                      ret  = clk_enable(xdev->clk);
> 
>  >
> 
>  > This is at the very least confusing.
> 
>  > The last action in the probe function is to call clk_disable_unprepare(),
> 
>  > meaning the clock should not be prepared here. How can it be enabled
> 
>  > without being prepared ?
> 
> Will update in V2
> 
>  >
> 
>  > > +                      if (ret) {
> 
>  > > +                                      dev_err(wdd->parent, "Failed to enable clock\n");
> 
>  > > +                                      return ret;
> 
>  > > +                      }
> 
>  > > +      }
> 
>  > > +
> 
>  > I think it would be better to separate the functions to start/stop the clock
> 
>  > from the function to update/enable the watchdog. The use of
> 
>  > watchdog_active() combined with
> 
>  > clk_enable/clk_disable/clk_prepare_enable/clk_disable_unprepare
> 
>  > is confusing and makes it all but impossible to review the driver.
> 
>  >
> 
>  > > +      spin_lock(&xdev->spinlock);
> 
>  > > +      iowrite32(XWWDT_MWR_MASK, xdev->base +
> 
>  > XWWDT_MWR_OFFSET);
> 
>  > > +      iowrite32(~(u32)XWWDT_ESR_WEN_MASK,
> 
>  > > +                        xdev->base + XWWDT_ESR_OFFSET);
> 
>  > > +
> 
>  > > +      if (pre_timeout) {
> 
>  > > +                      iowrite32((u32)(time_out - pre_timeout),
> 
>  > > +                                        xdev->base + XWWDT_FWR_OFFSET);
> 
>  > > +                      iowrite32((u32)pre_timeout, xdev->base +
> 
>  > XWWDT_SWR_OFFSET);
> 
>  > > +                      fcr = ioread32(xdev->base + XWWDT_SWR_OFFSET);
> 
>  > > +                      fcr = (fcr >> XWWDT_SBC_SHIFT) & XWWDT_SBC_MASK;
> 
>  > > +                      fcr = fcr | XWWDT_BSS_MASK;
> 
>  > > +                      iowrite32(fcr, xdev->base + XWWDT_FCR_OFFSET);
> 
>  > > +      } else {
> 
>  > > +                      iowrite32((u32)pre_timeout,
> 
>  > > +                                        xdev->base + XWWDT_FWR_OFFSET);
> 
>  > > +                      iowrite32((u32)time_out, xdev->base +
> 
>  > XWWDT_SWR_OFFSET);
> 
>  > > +                      iowrite32(0x0, xdev->base + XWWDT_FCR_OFFSET);
> 
>  > > +      }
> 
>  > > +
> 
>  > > +      /* Enable the window watchdog timer */
> 
>  > > +      control_status_reg = ioread32(xdev->base + XWWDT_ESR_OFFSET);
> 
>  > > +      control_status_reg |= XWWDT_ESR_WEN_MASK;
> 
>  > > +      iowrite32(control_status_reg, xdev->base + XWWDT_ESR_OFFSET);
> 
>  > > +
> 
>  > > +      spin_unlock(&xdev->spinlock);
> 
>  > > +
> 
>  > > +      dev_dbg(xilinx_wwdt_wdd->parent, "Watchdog Started!\n");
> 
>  > > +
> 
>  > > +      return 0;
> 
>  > > +}
> 
>  > > +
> 
>  > > +static int xilinx_wwdt_stop(struct watchdog_device *wdd) {
> 
>  > > +      struct xwwdt_device *xdev = watchdog_get_drvdata(wdd);
> 
>  > > +      struct watchdog_device *xilinx_wwdt_wdd = &xdev-
> 
>  > >xilinx_wwdt_wdd;
> 
>  > > +
> 
>  > > +      if (!is_wwdt_in_closed_window(wdd)) {
> 
>  > > +                      dev_warn(xilinx_wwdt_wdd->parent, "timer in closed
> 
>  > window");
> 
>  > > +                      return -EINVAL;
> 
>  > > +      }
> 
>  > > +
> 
>  > > +      spin_lock(&xdev->spinlock);
> 
>  > > +
> 
>  > > +      iowrite32(XWWDT_MWR_MASK, xdev->base +
> 
>  > XWWDT_MWR_OFFSET);
> 
>  > > +      /* Disable the Window watchdog timer */
> 
>  > > +      iowrite32(~(u32)XWWDT_ESR_WEN_MASK,
> 
>  > > +                        xdev->base + XWWDT_ESR_OFFSET);
> 
>  > > +
> 
>  > > +      spin_unlock(&xdev->spinlock);
> 
>  > > +
> 
>  > > +      if (watchdog_active(xilinx_wwdt_wdd))
> 
>  > > +                      clk_disable(xdev->clk);
> 
>  > > +
> 
>  >
> 
>  > The stop function won't be called if the watchdog is not running, ie if
> 
>  > watchdog_active() returns false.
> 
>  > I don't undeerstand the logic of clock handling in this driver.
> 
>  > More on that below.
> 
>  >
> 
>  > > +      dev_dbg(xilinx_wwdt_wdd->parent, "Watchdog Stopped!\n");
> 
>  > > +
> 
>  > > +      return 0;
> 
>  > > +}
> 
>  > > +
> 
>  > > +static int xilinx_wwdt_keepalive(struct watchdog_device *wdd) {
> 
>  > > +      u32 control_status_reg;
> 
>  > > +      struct xwwdt_device *xdev = watchdog_get_drvdata(wdd);
> 
>  > > +
> 
>  > > +      /* Refresh in open window is ignored */
> 
>  > > +      if (!is_wwdt_in_closed_window(wdd))
> 
>  > > +                      return 0;
> 
>  > > +
> 
>  > This is dangerous. There is no reason for userspace to adhere to these
> 
>  > restrictions.
> 
>  >
> 
>  > > +      spin_lock(&xdev->spinlock);
> 
>  > > +
> 
>  > > +      iowrite32(XWWDT_MWR_MASK, xdev->base +
> 
>  > XWWDT_MWR_OFFSET);
> 
>  > > +      control_status_reg = ioread32(xdev->base + XWWDT_ESR_OFFSET);
> 
>  > > +      control_status_reg |= XWWDT_ESR_WINT_MASK;
> 
>  > > +      control_status_reg &= ~XWWDT_ESR_WSW_MASK;
> 
>  > > +      iowrite32(control_status_reg, xdev->base + XWWDT_ESR_OFFSET);
> 
>  > > +      control_status_reg = ioread32(xdev->base + XWWDT_ESR_OFFSET);
> 
>  > > +      control_status_reg |= XWWDT_ESR_WSW_MASK;
> 
>  > > +      iowrite32(control_status_reg, xdev->base + XWWDT_ESR_OFFSET);
> 
>  > > +
> 
>  > > +      spin_unlock(&xdev->spinlock);
> 
>  > > +
> 
>  > > +      return 0;
> 
>  > > +}
> 
>  > > +
> 
>  > > +static int xilinx_wwdt_set_timeout(struct watchdog_device *wdd,
> 
>  > > +                                                         unsigned int new_time)
> 
>  > > +{
> 
>  > > +      u32 ret = 0;
> 
>  > > +      struct xwwdt_device *xdev = watchdog_get_drvdata(wdd);
> 
>  > > +      struct watchdog_device *xilinx_wwdt_wdd = &xdev-
> 
>  > >xilinx_wwdt_wdd;
> 
>  > > +
> 
>  > > +      if (!is_wwdt_in_closed_window(wdd)) {
> 
>  > > +                      dev_warn(xilinx_wwdt_wdd->parent, "timer in closed
> 
>  > window");
> 
>  > > +                      return -EINVAL;
> 
>  > > +      }
> 
>  > > +
> 
>  >
> 
>  > So userspace can clog the log by continuously trying to set the timeout ?
> 
>  >
> 
>  > Also, again, this is dangerous. Userspace does not know the window size.
> 
> user can configure window size.
> 
>  >
> 
>  >
> 
>  > > +      if (new_time < XWWDT_MIN_TIMEOUT ||
> 
>  > > +          new_time > XWWDT_MAX_TIMEOUT) {
> 
>  > > +                      dev_warn(xilinx_wwdt_wdd->parent,
> 
>  > > +                                      "timeout value must be %d<=x<=%d, using %d\n",
> 
>  > > +                                      XWWDT_MIN_TIMEOUT,
> 
>  > > +                                      XWWDT_MAX_TIMEOUT, new_time);
> 
>  > > +                      return -EINVAL;
> 
>  > > +      }
> 
>  >
> 
>  > This is handled by the watchdog core.
> 
>  >
> 
>  > > +
> 
>  > > +      wdd->timeout = new_time;
> 
>  > > +      wdd->pretimeout = 0;
> 
>  > > +
> 
>  > > +      if (watchdog_active(xilinx_wwdt_wdd)) {
> 
>  > > +                      ret = xilinx_wwdt_start(wdd);
> 
>  > > +                      if (ret)
> 
>  > > +                                      dev_dbg(xilinx_wwdt_wdd->parent, "timer start
> 
>  > failed");
> 
>  > > +      }
> 
>  > > +
> 
>  > > +      return ret;
> 
>  > > +}
> 
>  > > +
> 
>  > > +static int xilinx_wwdt_set_pretimeout(struct watchdog_device *wdd,
> 
>  > > +                                                            u32 new_pretimeout)
> 
>  > > +{
> 
>  > > +      u32 ret = 0;
> 
>  > > +      struct xwwdt_device *xdev = watchdog_get_drvdata(wdd);
> 
>  > > +      struct watchdog_device *xilinx_wwdt_wdd = &xdev-
> 
>  > >xilinx_wwdt_wdd;
> 
>  > > +
> 
>  > > +      if (!is_wwdt_in_closed_window(wdd)) {
> 
>  > > +                      dev_warn(xilinx_wwdt_wdd->parent, "timer in closed
> 
>  > window");
> 
>  > > +                      return -EINVAL;
> 
>  > > +      }
> 
>  >
> 
>  > This restriction is not only dangerous but confusing, and simply unacceptable.
> 
>  > Userspace will get -EINVAL with no idea what is wrong.
> 
>  > A watchdog daemon will bail out for no good reason.
> 
>  >
> 
>  > > +
> 
>  > > +      if (new_pretimeout < wdd->min_timeout ||
> 
>  > > +          new_pretimeout >= wdd->timeout)
> 
>  > > +                      return -EINVAL;
> 
>  > > +
> 
>  > This is handled by the watchdog core.
> 
>  >
> 
>  > > +      wdd->pretimeout = new_pretimeout;
> 
>  > > +
> 
>  > > +      if (watchdog_active(xilinx_wwdt_wdd)) {
> 
>  > > +                      ret = xilinx_wwdt_start(wdd);
> 
>  > > +                      if (ret)
> 
>  > > +                                      dev_dbg(xilinx_wwdt_wdd->parent, "timer start
> 
>  > failed");
> 
>  > > +      }
> 
>  > > +
> 
>  > > +      return ret;
> 
>  > > +}
> 
>  > > +
> 
>  > > +static void xwwdt_clk_disable_unprepare(void *data) {
> 
>  > > +      clk_disable_unprepare(data);
> 
>  > > +}
> 
>  > > +
> 
>  > > +static irqreturn_t xilinx_wwdt_isr(int irq, void *wdog_arg) {
> 
>  > > +      struct xwwdt_device *xdev = wdog_arg;
> 
>  > > +
> 
>  > > +      watchdog_notify_pretimeout(&xdev->xilinx_wwdt_wdd);
> 
>  > > +
> 
>  > > +      return IRQ_HANDLED;
> 
>  > > +}
> 
>  > > +
> 
>  > > +static const struct watchdog_info xilinx_wwdt_ident = {
> 
>  > > +      .options = WDIOF_MAGICCLOSE |
> 
>  > > +                         WDIOF_KEEPALIVEPING |
> 
>  > > +                         WDIOF_SETTIMEOUT,
> 
>  > > +      .firmware_version = 1,
> 
>  > > +      .identity = "xlnx_window watchdog",
> 
>  > > +};
> 
>  > > +
> 
>  > > +static const struct watchdog_info xilinx_wwdt_pretimeout_ident = {
> 
>  > > +      .options = WDIOF_MAGICCLOSE |
> 
>  > > +                         WDIOF_KEEPALIVEPING |
> 
>  > > +                         WDIOF_PRETIMEOUT |
> 
>  > > +                         WDIOF_SETTIMEOUT,
> 
>  > > +      .firmware_version = 1,
> 
>  > > +      .identity = "xlnx_window watchdog",
> 
>  > > +};
> 
>  > > +
> 
>  > > +static const struct watchdog_ops xilinx_wwdt_ops = {
> 
>  > > +      .owner = THIS_MODULE,
> 
>  > > +      .start = xilinx_wwdt_start,
> 
>  > > +      .stop = xilinx_wwdt_stop,
> 
>  > > +      .ping = xilinx_wwdt_keepalive,
> 
>  > > +      .set_timeout = xilinx_wwdt_set_timeout,
> 
>  > > +      .set_pretimeout = xilinx_wwdt_set_pretimeout, };
> 
>  > > +
> 
>  > > +static int xwwdt_probe(struct platform_device *pdev) {
> 
>  > > +      struct device *dev = &pdev->dev;
> 
>  > > +      struct watchdog_device *xilinx_wwdt_wdd;
> 
>  > > +      struct xwwdt_device *xdev;
> 
>  > > +      u32 pre_timeout = 0;
> 
>  > > +      int ret;
> 
>  > > +
> 
>  > > +      xdev = devm_kzalloc(dev, sizeof(*xdev), GFP_KERNEL);
> 
>  > > +      if (!xdev)
> 
>  > > +                      return -ENOMEM;
> 
>  > > +
> 
>  > > +      xilinx_wwdt_wdd = &xdev->xilinx_wwdt_wdd;
> 
>  > > +      xilinx_wwdt_wdd->info = &xilinx_wwdt_ident;
> 
>  > > +      xilinx_wwdt_wdd->ops = &xilinx_wwdt_ops;
> 
>  > > +      xilinx_wwdt_wdd->parent = dev;
> 
>  > > +
> 
>  > > +      xdev->base = devm_platform_ioremap_resource(pdev, 0);
> 
>  > > +      if (IS_ERR(xdev->base))
> 
>  > > +                      return PTR_ERR(xdev->base);
> 
>  > > +
> 
>  > > +      ret = of_property_read_u32(dev->of_node, "pretimeout-sec",
> 
>  > > +                                                         &pre_timeout);
> 
>  > > +      if (ret)
> 
>  > > +                      dev_dbg(dev,
> 
>  > > +                                      "Parameter \"pretimeout-sec\" not found\n");
> 
>  > > +
> 
>  > > +      xdev->clk = devm_clk_get(dev, NULL);
> 
>  > > +      if (IS_ERR(xdev->clk))
> 
>  > > +                      return PTR_ERR(xdev->clk);
> 
>  > > +
> 
>  > > +      ret = clk_get_rate(xdev->clk);
> 
>  > > +      if (!ret)
> 
>  > > +                      return -EINVAL;
> 
>  > > +
> 
>  > > +      ret = clk_prepare_enable(xdev->clk);
> 
>  > > +      if (ret) {
> 
>  > > +                      dev_err(dev, "unable to enable clock\n");
> 
>  > > +                      return ret;
> 
>  > > +      }
> 
>  > > +      ret = devm_add_action_or_reset(dev,
> 
>  > xwwdt_clk_disable_unprepare,
> 
>  > > +                                                             xdev->clk);
> 
>  > > +      if (ret)
> 
>  > > +                      goto err_clk_disable;
> 
>  > > +
> 
>  >
> 
>  > Seems pointless. What happens when you unload the driver ?
> 
>  >
> 
>  > > +      xilinx_wwdt_wdd->pretimeout = pre_timeout;
> 
>  > > +      xilinx_wwdt_wdd->timeout = XWWDT_DEFAULT_TIMEOUT;
> 
>  > > +      xilinx_wwdt_wdd->min_timeout = XWWDT_MIN_TIMEOUT;
> 
>  > > +      xilinx_wwdt_wdd->max_timeout = XWWDT_MAX_TIMEOUT;
> 
>  > > +
> 
>  > > +      xdev->irq = platform_get_irq_byname(pdev, "wdt");
> 
>  > > +      if (xdev->irq < 0) {
> 
>  > > +                      ret = xdev->irq;
> 
>  > > +                      goto err_clk_disable;
> 
>  > > +      }
> 
>  > > +
> 
>  > > +      if (!devm_request_irq(dev, xdev->irq, xilinx_wwdt_isr,
> 
>  > > +                                            0, dev_name(dev), xdev)) {
> 
>  > > +                      xilinx_wwdt_wdd->info = &xilinx_wwdt_pretimeout_ident;
> 
>  > > +      }
> 
>  > > +
> 
>  > > +      ret = watchdog_init_timeout(xilinx_wwdt_wdd,
> 
>  > > +                                                          wwdt_timeout, &pdev->dev);
> 
>  > > +      if (ret)
> 
>  > > +                      dev_info(&pdev->dev, "Configured default timeout
> 
>  > value\n");
> 
>  > > +
> 
>  > > +      spin_lock_init(&xdev->spinlock);
> 
>  > > +      watchdog_set_drvdata(xilinx_wwdt_wdd, xdev);
> 
>  > > +
> 
>  > > +      ret = devm_watchdog_register_device(dev, xilinx_wwdt_wdd);
> 
>  > > +      if (ret)
> 
>  > > +                      goto err_clk_disable;
> 
>  > > +
> 
>  > At this point the watchdog is fully instantiated, and userspace may have
> 
>  > enabled it.
> 
>  >
> 
>  > > +      clk_disable_unprepare(xdev->clk);
> 
>  > > +
> 
>  > And now its clock is getting stopped. Actually, it is getting unprepared.
> 
>  > Does this even work ?
> 
>  >
> 
>  > > +      dev_info(dev, "Xilinx Window Watchdog Timer with timeout %ds\n",
> 
>  > > +                      xilinx_wwdt_wdd->timeout);
> 
>  > > +
> 
>  > > +      return 0;
> 
>  > > +
> 
>  > > +err_clk_disable:
> 
>  > > +      clk_disable_unprepare(xdev->clk);
> 
>  >
> 
>  > devm_add_action_or_reset() already handles this.
> 
>  >
> 
>  > > +      return ret;
> 
>  > > +}
> 
>  > > +
> 
>  > > +/* Mat for of_platform binding */
> 
>  > > +static const struct of_device_id xwwdt_of_match[] = {
> 
>  > > +      { .compatible = "xlnx,versal-wwdt-1.0", },
> 
>  > > +      {},
> 
>  > > +};
> 
>  > > +MODULE_DEVICE_TABLE(of, xwwdt_of_match);
> 
>  > > +
> 
>  > > +static struct platform_driver xwwdt_driver = {
> 
>  > > +      .probe = xwwdt_probe,
> 
>  > > +      .driver = {
> 
>  > > +                      .name = "Xilinx Window Watchdog",
> 
>  > > +                      .of_match_table = xwwdt_of_match,
> 
>  > > +      },
> 
>  > > +};
> 
>  > > +
> 
>  > > +module_platform_driver(xwwdt_driver);
> 
>  > > +
> 
>  > > +MODULE_AUTHOR("Neeli Srinivas <sneeli@xilinx.com <mailto:sneeli@xilinx.com>>");
> 
>  > > +MODULE_DESCRIPTION("Xilinx Window Watchdog driver");
> 
>  > > +MODULE_LICENSE("GPL");
> 
>  > >
> 
> Thanks
> 
> Srinivas Neeli.
>